document_title: I Can Only Imagine (film)

question_text: who played amy grant i i can only imagine

text: I Can Only Imagine (film)

text: Plot[edit]

text: Coming from a home with an abusive father, 10-year-old Bart Millard is dropped off at a Christian camp by his mother, where he meets Shannon. Upon his return from camp, Bart finds his mother has left and movers are removing her belongings, leading to a physical confrontation with his father Arthur, who takes custody of him.

text: Years later, Millard is in high school and dating Shannon. Hoping to impress his father, he begins playing football. However, he is injured, breaking both ankles and ending his career. In order to make up the credits he would miss from football, he signs up for music class, the only available class left. Initially, Millard is assigned to be a sound technician. After the director catches him singing in the empty auditorium, she casts him as Curly, the lead role in the school production of Oklahoma. He doesn't tell his father of his role in the play, and while Bart has risen to the singing demands of the part, Arthur subsequently collapses with severe abdominal pain, but refuses to tell Bart or Shannon about his cancer diagnosis. The following morning, Millard voices his frustrations with his father and is assaulted by his father, who smashes a plate over his head. Shannon presses Bart to open up, but he responds by breaking up with her and leaving to seek his fortune in the city after graduation.

text: Millard then connects with the band who would become MercyMe, and eventually attracts the attention of Christian music producer Scott Brickell, who coaches Millard and gets them a showcase in Nashville, leading to meetings with Amy Grant and Michael W. Smith. Millard has been unable to reconcile with Shannon, who rejects his invitation to tour with the band to their upcoming Nashville showcase. While the band felt their performance was the best of their career, industry representatives reject the band as not being good enough to sell records. In despair, Millard quits the band. After talking with Brickell, who encourages him to resolve his issues with his father, Millard rejoins the band but asks they wait for him to confront his father and settle the conflict before they play again.

text: Millard returns home and is greeted enthusiastically by his father, who prepares breakfast for him the next morning. His father claims to have become a Christian, but Bart is initially skeptical and rejects his father's offer to start over. In anger, Arthur takes a baseball bat and hits his old Jeep, which he had hoped to repair with his son. As Bart prepares to leave, he finds out his father has terminal cancer. Bart and his father reconcile and form a deep bond before Arthur dies of his illness.

text: After his father's funeral, Millard rejoins the band and writes "I Can Only Imagine". Brickell sends the demo tape to several artists, including Grant, who, deeply moved by the song, asks to record it herself as her next single. The band accepts Grant's offer. Millard is seated in the audience when Grant intends to unveil the song live in concert. However, Grant decides that Millard should be the one to sing the song, and offers it back to him, calling him to the microphone to sing it before the large audience. Millard's unexpected performance is wildly applauded and he reunites with Shannon, who had also been in attendance at the concert. The band releases the song as their first single, achieving success on Christian and mainstream radio.

text: Cast[edit]

text:
J. Michael Finley as Bart Millard

Brody Rose as Young Bart

Dennis Quaid as Arthur Millard, Bart's father
Cloris Leachman as Meemaw, Bart's grandmother
Madeline Carroll as Shannon, Bart's girlfriend

Taegen Burns as Young Shannon

Trace Adkins as Scott Brickell, MercyMe's manager
Priscilla Shirer as Mrs. Fincher, Bart's teacher
Nicole DuPort as Amy Grant
Jake B. Miller as Michael W. Smith
Mark Furze as Nathan

tag: ul

text: Production[edit]

text: This section needs expansion. You can help by adding to it. (March 2018)

text: The film was announced in December 2016.[4] Dennis Quaid joined the cast in January 2017.[5] Broadway actor J. Michael Finley makes his film debut as Bart Millard.[1] The same month, it was announced that the film was slated for release in the spring of 2018.[5] In August 2017, Lionsgate and Roadside Attractions signed on as distributors for the film for a nationwide release in the United States.[1][6]

text: Reception[edit]

text: Box office[edit]

text: As of April 22, 2018[update], I Can Only Imagine has grossed $79.4 million in the United States, and Canada and $1 million in other territories, for a worldwide total of $80.4 million, against a production budget of $7 million.[2] It is the third-highest grossing music biopic of all-time in the United States, behind Straight Outta Compton and Walk the Line.[7]

text: The film was released on March 16, 2018, alongside Tomb Raider and Love, Simon, and was originally projected to gross $2–4 million from 1,620 theaters in its opening weekend.[8] However, after making $6.2 million on its first day (including $1.3 million from Thursday night previews), weekend estimates were increased to $14 million.[9] It ended up grossing $17.1 million, exceeding expectations and finishing third at the box office behind Black Panther and Tomb Raider. 67% of the opening weekend audience was female while 80% was over the age of 35.[10] It was the fourth best-ever opening for a faith-based film, following The Passion of the Christ ($83.8 million), Son of God ($25.6 million) and Heaven Is for Real ($22.5 million).[11] In its second weekend the film was added to 624 additional theaters and dropped just 19% to $13.8 million, again finishing third.[12] It was added to another 395 venues and finished fourth in its third weekend, making $10.4 million (including $3 million on Easter Sunday).[13]

text: Critical response[edit]

text: On review aggregator website Rotten Tomatoes, the film holds an approval rating of 70% based on 23 reviews, and an average rating of 6/10. The site's critical consensus reads, "I Can Only Imagine's message will have the most impact among Christian audiences, but overall, its performances and storytelling represent a notable evolution in faith-based cinema."[14] On Metacritic, the film has a weighted average score of 29 out of 100, based on 7 critics, indicating "generally unfavorable reviews".[15] Audiences polled by CinemaScore gave the film an average grade of "A+" on an A+ to F scale, one of fewer than 80 films in the history of the service to earn such a score.[9]

text: The Arizona Republic's James Ward gave the film 4/5 stars and wrote, "Too often faith-based films — say anything with Kirk Cameron or the terrible God's Not Dead series — tend to preach to the choir or hector their audience. The Erwins’ films — I Can Only Imagine definitely among them — are more inclusive, charitable of spirit and hopeful, all qualities that are always appreciated, be they rooted in Christian faith or otherwise."[16] David Ehrlich of IndieWire gave the film a "C–" saying: "There’s a reason why all of these movies are so amateurishly made; why they all end with links to religious websites; why they all look like they were shot on an iPhone by a Walmart-brand Janusz Kaminski who lit each interior like the white light of heaven was streaming through every window...Art can be affirmation, but affirmation cannot be art."[17]


document_title: Tiger Zinda Hai

question_text: who played the villain in tiger zinda hai

root

text: Tiger Zinda Hai

text: Plot

text: Eight years have passed since the events of Ek Tha Tiger and the whereabouts of Tiger and Zoya are not known. In Ikrit, Syria, 40 nurses – 25 Indian and 15 Pakistani – are held hostage in their own hospital by Abu Usman, the head of ISC, a terrorist organisation. The chairman of the Research and Analysis Wing (RAW), Shenoy, feels that only Tiger would be able to rescue the nurses and that too within a period of 7 days as the United States will launch an airstrike within 7 days to kill Usman. Presently, Tiger and Zoya live in Innsbruck, Austria and have a son, Junior.

tag: p

text: Shenoy and his deputy, Karan manage to find Tiger and requests him to undertake the mission. Although hesitant at first, Tiger agrees after Zoya asks him to carry out the mission for his country. Tiger and three other RAW agents Azaan, Namit and Rakesh travel to Syria. Meanwhile, Zoya comes to know of the Pakistani nurses held hostage along with the Indians and joins Tiger with two other ISI members Abrar and Javed.

text: On the day of the airstrike, Tiger managed to rescue the nurses from the hospital. Meanwhile, Abu Usman holds Zoya hostage and captures Tiger, who is put into a poison chamber. Tiger, Zoya and the nurses flee after Tiger defeats Abu Usman and his troops. Tiger and Zoya go into hiding once again due to Tiger's belief that the RAW will never forgive him for deserting them, but tells Shenoy he will always be there if his country is in trouble.

text: Cast

text:
Salman Khan as Avinash "Tiger" Singh Rathore[14]
Katrina Kaif as Zoya[15]
Sajjad Delafrooz [16] as Abu Usman
Paresh Rawal as Firdauz aka Tohbaan[17]
Angad Bedi as Namit[18]
Kumud Mishra as Rakesh
Girish Karnad as Shenoy
Neha Hinge as Maria
Gavie Chahal as Captain Abrar
Danish Bhatt as Captain Javed
Anupriya Goenka as Poorna
Anant Vidhaat Sharma as Karan
Ivan Rodrigues as India's Ambassador to Iraq
Nawab Shah as Pawan
Zachary Coffin as Gary
Casey Shannon as Sam Jacobs
Siddhartha Basu as Indian Defense Minister.
Rohit KaduDeshmukh as Rohit
Paresh Pahuja as Azaan
Najmeddin Al Hadad as Hakim
Vibhoutee Sharma as Jiya
Sartaaj Kakkar as Junior
Jineet Rath as Hasaan
Anjana Om Kashyap as Herself (Indian TV Reporter)

text: Production

text: Filming took place in Abu Dhabi, Austria, Greece and Morocco.[19] The last song of the movie was shot in the Aegean island of Naxos, Greece in October 2017.[20] Iranian actor Sajjad Delafrooz was roped in to play the role of Abu Usman, leader of terrorist organisation ISC.[16] Sajjad Delafrooz had worked in the 2015 Hindi film Baby.[21]

text: The film's production budget is reportedly ₹210 crore (US$33 million),[2] or ₹140 crore (US$22 million) excluding Salman Khan's fees.[22] This would make it one of the most expensive Yash Raj Films productions, along with Dhoom 3, Sultan and Thugs of Hindostan.[22]

text: Marketing and release

text: The film's trailer was released on 6 November 2017. Within 24 hours, it broke many records for Hindi film trailers on YouTube, with more than 29 million views, 480 thousand likes and 250 thousand shares.[23] On 11 November, it became the most liked film trailer on YouTube with 700 thousand likes, surpassing Star Wars: The Force Awakens (2015) then.[24] The record was later surpassed by the trailer of Avengers: Infinity War (2018) with about 2 million likes.[25]

text: The film was released on 22 December 2017 worldwide. The film received U/A certificate from Central Board of Film Certification.[26] Despite having a song featuring Pakistani singer Atif Aslam, the film has not been given No-Objection Certificate by Central Board of Film Censors in Pakistan, stating the reason as was said for Ek Tha Tiger that "The image of Pakistan and its law enforcement agencies" have been compromised.[27][28]

text: Tiger Zinda Hai was in controversy on its release and faced protests from Valmiki community,[29] when Salman Khan allegedly made a casteist slur, where he compared his dancing skills to a sanitation worker, "or "bhangi" in a dance show. Shilpa Shetty also laughed along with him, and said that she also looked like one.[30] Valmiki group is made up of a cluster of dalit communities — a few of whom are Bhangi, Mehtar, Chuhra, Lal Beghi and Halalkhor. Valmiki commmunity filed a legal case against both actors for hurting their sentiments.[31]

text: Maharashtra Navnirman Sena also unsuccessfully protested urging Mumbai multiplexes to promote Marathi film Deva instead of Tiger Zinda Hai.[32] Their leaders raised issue about the loss of screens to Marathi films like Deva and Ek Atrangi which released alongside.[33]

text: Critical reception

text: Tiger Zinda Hai opened to generally favourable reviews.[34] Taran Adarsh of Bollywood Hungama gave 4.5 stars, and said "Salman is the lifeline, the real treasure of Tiger Zinda Hai. He sinks his teeth into the character and, in several sequences, peels off the mask of super-stardom and brings the actor to the fore. Katrina is in solid form, in action sequences specifically. Commands attention."[35] Umesh Punwani of Koimoi gave 4 stars, and said "Katrina Kaif is brilliant! She has very few dialogues, and no that's not the reason she's good. Working amazingly well with her expressions, she has turned into an athlete for this one. Performing few major action sequences, she is flawless."[36] Aarti Jhurani of The National gave 4 stars, and said "While logic is not a very important factor in Khan's films, emotions certainly are, and the director made sure to hit all the soft spots – from patriotism to Indo-Pakistan bonding to a multitude of cheesy dialogues – which is a smart move, and sure to bring in both Indian and Pakistani audiences."[37] Lasyapriya Sundaram of The Times of India gave 3.5 stars, and said "The film is visually stunning in parts and Salman Khan plays Tiger with roaring confidence and dialogues packed with punch. Of course, his fans get a true-blue Salman Khan moment when he bares his torso."[38] Rachit Gupta of Filmfare gave 3.5 stars, and said "It may look like a Hollywood action thriller, but at its heart, Tiger Zinda Hai is an unabashed masala movie. The heady mixture of an international looking action film and the regular tropes of Hindi cinema make it a pleasing watch."[39]

text: Rohit Bhatnagar of Deccan Chronicle gave 3 stars, and said "Ali Abbas Zafar smoothly takes Ek Tha Tiger franchise ahead by telling a real story and inserting whole lot of drama and thrill. The film also touches upon relationships between India and Pakistan but subtly. The biggest hiccup of the film is its length."[40] Rajeev Masand of News 18 gave 3 stars, and said "The film has some thrilling action, while logic and subtlety are sacrificed at the altar of spectacle and sentiment. Katrina gets some terrific action moments and she executes them well, but make no mistake, the heavy lifting here is left to Salman Khan, and he's clearly up for the challenge."[41]

text: Raja Sen of NDTV India gave 2.5 stars, and said "Tiger Zinda Hai breaks for intermission at a point when most self-respecting action films would have rushed into the climax. Long before the finish eventually rolled around, I found myself wishing Tiger would croak just so I could make it out alive."[42] Rohit Vats of Hindustan Times gave 2.5 stars, and said "It's better for the filmmakers to set a character trajectory that matches the star's current image rather than basking in the glory of the past."[43] Anna M. M. Vetticad of Firstpost gave 2.5 stars, stating that both Salman Khan and Katrina Kaif delivered fun with equal parts swag, silliness and schmaltz.[44] Shubhra Gupta of Indian Express gave 2.5 stars, and said "Only once in a while, the film gives in and provides us a killing which sobers us up, but very quickly it's back to the base, with Bhai taking over, and everyone including Nurse Poorna and Zoya making way for him. But you can see she enjoys kicking butt: you wish she had more to do."[45]

text: Box office

text: Tiger Zinda Hai made a new non-holiday record in India as it collected ₹34.1 crore nett on its first day.[46] It went on to collect ₹35.30 crore nett gross on second day. The film recorded the second highest day of all time (after third day of Bahubali 2: The Conclusion) on its third day with net-gross of ₹45.53 crore and the highest ever for the Hindi film industry.[47] With three day nett gross collections of over ₹1.14 billion, Tiger Zinda Hai had the second highest opening weekend of all time (after Bahubali 2: The Conclusion) and the highest opening weekend of all time in the Bollywood film industry.[48] Tiger Zinda Hai grossed Rs 154 crore in first four days in India.[49][50]

text: Tiger Zinda Hai grossed $2 million in two days, $450,000 on day one in US/Canada and around £150,000 in the UK.[51] The film grossed $7 million in its opening weekend in overseas, including $2,535,825 in US/Canada.[52][53] The film grossed ₹190 crore worldwide in its opening weekend.[54] As of 23 January 2018, the film has grossed ₹552 crore (US$87 million) worldwide,[3] including at least ₹427.67 crore (US$67 million) in India[55] and ₹122.98 crore (US$19 million) overseas.[56]

text: Soundtrack

text:
Tiger Zinda Hai

Soundtrack album by Vishal–Shekhar

Released
12 December 2017 (2017-12-12)

Recorded
2017

Genre
Feature film soundtrack

Length
25:26

Label
YRF Music

Producer
Aditya Chopra

Vishal–Shekhar chronology

Befikre
(2016)
Tiger Zinda Hai
(2017)
Raazi
(upcoming)

External audio

 Audio Jukebox on YouTube

tag: table

text: The film score was composed by Julius Packiam. The soundtrack album featuring the main theme by Packiam and 6 songs composed by Vishal Shekar was released on 12 December 2017 by YRF Music. The Arabic version of "Swag Se Swagat" was sung by Rabih Baroud and Brigitte Yaghi.[57]

text: All lyrics written by Irshad Kamil.

text:
Tracklist

No.
Title
Singer(s)
Length

1.
"Swag Se Swagat"
Vishal Dadlani & Neha Bhasin
03:55

2.
"Dil Diyan Gallan"
Atif Aslam
04:20

3.
"Zinda Hai" (Tiger Theme by Julius Packiam)
Sukhwinder Singh, Rap by Raftaar
04:13

4.
"Daata Tu"
Shreya Ghoshal
04:13

5.
"Tera Noor"
Jyoti Nooran
04:42

6.
"Dil Diyan Gallan" (Unplugged)
Neha Bhasin
04:03

Total length:
25:26

text: Awards and nominations

text:
Date of Ceremony
Award
Category
Recipient(s) and nominee(s)
Result
Ref.

16 January 2018
3rd FOI Online Awards, India
Best Action Direction
Tom Struthers
Won
[58]

20 January 2018
63rd Filmfare Awards
Best Action
Tom Struthers
Won
[13]


document_title: Division of Korea

question_text: when did korea separate into north and south

text: Division of Korea

text: Historical background[edit]

text: Korea under Japanese rule (1910–1945)[edit]

text: When the Russo-Japanese War ended in 1905 Korea became a nominal protectorate of Japan, and was annexed by Japan in 1910. The Korean king Gojong was removed. In the following decades, nationalist and radical groups emerged, mostly in exile, to struggle for independence. Divergent in their outlooks and approaches, these groups failed to unite in one national movement.[1][2] The Korean Provisional Government in China failed to obtain widespread recognition.[3]

text: End of World War II[edit]

text: In November 1943, Franklin Roosevelt, Winston Churchill and Chiang Kai-shek met at the Cairo Conference to discuss what should happen to Japan's colonies, and agreed that Japan should lose all the territories it had conquered by force. In the declaration after this conference, Korea was mentioned for the first time. The three powers declared that they were, "mindful of the enslavement of the people of Korea, ... determined that in due course Korea shall become free and independent."[4][5] Roosevelt floated the idea of a trusteeship over Korea, but did not obtain agreement from the other powers. Roosevelt raised the idea with Joseph Stalin at the Tehran Conference in November 1943 and the Yalta Conference in February 1945. Stalin did not disagree, but advocated that the period of trusteeship be short.[6][7]

text: At the Tehran Conference and the Yalta Conference, the Soviet Union promised to join its allies in the Pacific War in two to three months after victory in Europe. On August 8, 1945, three months to the day after the end of hostilities in Europe, and two days after the atomic bomb was dropped on Hiroshima, the Soviet Union declared war on Japan.[8] Soviet troops advanced rapidly, and the US government became anxious that they would occupy the whole of Korea. On August 10, 1945 two young officers – Dean Rusk and Charles Bonesteel – were assigned to define an American occupation zone. Working on extremely short notice and completely unprepared, they used a National Geographic map to decide on the 38th parallel. They chose it because it divided the country approximately in half but would place the capital Seoul under American control. No experts on Korea were consulted. The two men were unaware that forty years before, Japan and pre-revolutionary Russia had discussed sharing Korea along the same parallel. Rusk later said that had he known, he "almost surely" would have chosen a different line.[9][10] The division placed sixteen million Koreans in the American zone and nine million in the Soviet zone.[11] To the surprise of the Americans, the Soviet Union immediately accepted the division. The agreement was incorporated into General Order No. 1 (approved on 17 August 1945) for the surrender of Japan.[12]

text: Soviet forces began amphibious landings in Korea by August 14 and rapidly took over the north-east of the country, and on August 16 they landed at Wonsan.[13] On August 24, the Red Army reached Pyongyang.[12]

text: General Abe Nobuyuki, the last Japanese Governor-General of Korea, had established contact with a number of influential Koreans since the beginning of August 1945 to prepare the hand-over of power. Throughout August, Koreans organized people's committee branches for the "Committee for the Preparation of Korean Independence" (CPKI, 조선건국준비위원회), headed by Lyuh Woon-hyung, a left-wing politician. On September 6, 1945, a congress of representatives was convened in Seoul and founded the short-lived People's Republic of Korea.[14][15]

text: Post-World War II[edit]

text: In December 1945, at the Moscow Conference, the Allies agreed that the Soviet Union, the US, the Republic of China, and Britain would take part in a trusteeship over Korea for up to five years in the lead-up to independence. Many Koreans demanded independence immediately; however, the Korean Communist Party, which was closely aligned with the Soviet Communist party, supported the trusteeship.[16][17]

text: A Soviet-US Joint Commission met in 1946 and 1947 to work towards a unified administration, but failed to make progress due to increasing Cold War antagonism and to Korean opposition to the trusteeship.[18] Meanwhile, the division between the two zones deepened. The difference in policy between the occupying powers led to a polarization of politics, and a transfer of population between North and South.[19] In May 1946 it was made illegal to cross the 38th parallel without a permit.[20]

text: US occupation of South Korea[edit]

text: With the American government fearing Soviet expansion, and the Japanese authorities in Korea warning of a power vacuum, the embarkation date of the US occupation force was brought forward three times.[3]

text: On September 7, 1945, General Douglas MacArthur announced that Lieutenant General John R. Hodge was to administer Korean affairs, and Hodge landed in Incheon with his troops the next day. The Provisional Government of the Republic of Korea, which had operated from China, sent a delegation with three interpreters to Hodge, but he refused to meet with them.[21] Likewise, Hodge refused to recognize the newly formed People's Republic of Korea and its People's Committees, and outlawed it on 12 December.[22]

text: In September 1946, thousands of laborers and peasants rose up against the military government. This uprising was quickly defeated, and failed to prevent scheduled October elections for the South Korean Interim Legislative Assembly.

text: The ardent anti-communist Syngman Rhee, who had been the first president of the Provisional Government and later worked as a pro-Korean lobbyist in the US, became the most prominent politician in the South. Rhee pressured the American government to abandon negotiations for a trusteeship and create an independent Republic of Korea in the south.[23] On July 19, 1947, Lyuh Woon-hyung, the last senior politician committed to left-right dialogue, was assassinated by a right-winger.[24]

text: The occupation government conducted a number of military campaigns against left-wing insurgents. Over the course of the next few years, between 30,000[25] and 100,000 people were killed.[26]

text: Soviet occupation of North Korea[edit]

text: When Soviet troops entered Pyongyang, they found a local branch of the Committee for the Preparation of Korean Independence operating under the leadership of veteran nationalist Cho Man-sik.[27] The Soviet Army allowed these "People's Committees" (which were friendly to the Soviet Union) to function. Colonel-General Terentii Shtykov set up the Soviet Civil Administration, taking control of the committees and placing communists in key positions.

text: In February 1946 a provisional government called the Provisional People's Committee was formed under Kim Il-sung, who had spent the last years of the war training with Soviet troops in Manchuria. Conflicts and power struggles ensued at the top levels of government in Pyongyang as different aspirants maneuvered to gain positions of power in the new government. In March 1946 the provisional government instituted a sweeping land-reform program: land belonging to Japanese and collaborator landowners was divided and redistributed to poor farmers.[28] Organizing the many poor civilians and agricultural laborers under the people's committees, a nationwide mass campaign broke the control of the old landed classes. Landlords were allowed to keep only the same amount of land as poor civilians who had once rented their land, thereby making for a far more equal distribution of land. The North Korean land reform was achieved in a less violent way than in China or in Vietnam. Official American sources stated: "From all accounts, the former village leaders were eliminated as a political force without resort to bloodshed, but extreme care was taken to preclude their return to power."[29] The farmers responded positively; many collaborators and former landowners fled to the south, where some of them obtained positions in the new South Korean government. According to the U.S. military government, 400,000 northern Koreans went south as refugees.[30]

text: Key industries were nationalized. The economic situation was nearly as difficult in the north as it was in the south, as the Japanese had concentrated agriculture in the south and heavy industry in the north.

text: Soviet forces departed in 1948.[31]

text: UN intervention and the formation of separate governments[edit]

text: With the failure of the Joint Commission to make progress, the US brought the problem before the United Nations in September 1947. The Soviet Union opposed UN involvement. At that time, the US had more influence over the UN than the USSR.[32] The UN passed a resolution on November 14, 1947, declaring that free elections should be held, foreign troops should be withdrawn, and a UN commission for Korea, the United Nations Temporary Commission on Korea (UNTCOK), should be created. The Soviet Union boycotted the voting and did not consider the resolution to be binding, arguing that the UN could not guarantee fair elections. In the absence of Soviet co-operation, it was decided to hold UN-supervised elections in the south only.[33][34] Some UNTCOK delegates felt that the conditions in the south gave unfair advantage to right-wing candidates, but they were overruled.[35]

text: The decision to proceed with separate elections was unpopular among many Koreans, who rightly saw it as a prelude to a permanent division of the country. General strikes in protest against the decision began in February 1948.[20] In April, Jeju islanders rose up against the looming division of the country. South Korean troops were sent to repress the rebellion. Tens of thousands of islanders were killed and by one estimate, 70% of the villages were burned by the South Korean troops.[36] The uprising flared up again with the outbreak of the Korean War.[37]

text: In April 1948, a conference of organizations from the north and the south met in Pyongyang, but the conference produced no results. The southern politicians Kim Koo and Kim Kyu-sik attended the conference and boycotted the elections in the south, as did other politicians and parties.[38][39] Kim Koo was assassinated the following year.[40]

text: On May 10, 1948 the south held a general election. On August 15, the "Republic of Korea" formally took over power from the U.S. military, with Syngman Rhee as the first president. In the North, the "Democratic People's Republic of Korea" was declared on September 9, with Kim Il-sung as prime minister.

text: On December 12, 1948, the United Nations General Assembly accepted the report of UNTCOK and declared the Republic of Korea to be the "only lawful government in Korea".[41]

text: Unrest continued in the South. In October 1948, the Yeosu–Suncheon Rebellion took place, in which some regiments rejected the suppression of the Jeju uprising and rebelled against the government.[42] In 1949, the Syngman Rhee government established the Bodo League in order to keep an eye on its political opponents. The majority of the Bodo League's members were innocent farmers and civilians who were forced into membership.[43] The registered members or their families were executed at the beginning of the Korean War. On December 24, 1949, South Korean Army massacred Mungyeong citizens who were suspected communist sympathizers or their family and affixed blame to communists.[44]

text: Korean War[edit]

text: This division of Korea, after more than a millennium of being unified, was seen as controversial and temporary by both regimes. From 1948 until the start of the civil war on June 25, 1950, the armed forces of each side engaged in a series of bloody conflicts along the border. In 1950, these conflicts escalated dramatically when North Korean forces invaded South Korea, triggering the Korean War. The United Nations intervened to protect the South, sending a US-led force. As it occupied the south, the Democratic People's Republic of Korea attempted to unify Korea under its regime, initiating the nationalisation of industry, land reform, and the restoration of the People's Committees.[45]

text: While UN intervention was conceived as restoring the border at the 38th parallel, Syngman Rhee argued that the attack of the North had obliterated the boundary. Similarly UN Commander in Chief, General Douglas MacArthur stated that he intended to unify Korea, not just drive the North Korean forces back behind the border.[46] However, the North overran 90% of the south until a counter-attack by US-led forces. As the North Korean forces were driven from the south, South Korean forces crossed the 38th parallel on 1 October, and American and other UN forces followed a week later. This was despite warnings from the People's Republic of China that it would intervene if American troops crossed the parallel.[47] As it occupied the North, the Republic of Korea, in turn, attempted to unify the country under its regime, with the Korean National Police enforcing political indoctrination.[48] As US-led forces pushed into north, China unleashed a counter-attack which drove them back into the south.

text: In 1951, the front line stabilized near the 38th parallel, and both sides began to consider an armistice. Rhee, however, demanded the war continue until Korea was unified under his leadership.[49] The Communist side supported an armistice line being based on the 38th parallel, but the United Nations supported a line based on the territory held by each side, which was defensible, and this position prevailed.[50] The Korean Armistice Agreement was signed after three years of war. The two sides agreed to create a four-kilometer-wide buffer zone between the states, known as the Korean Demilitarized Zone (DMZ). This new border, reflecting the territory held by each side at the end of the war, crossed the 38th parallel diagonally. Rhee refused to accept the armistice and continued to urge the reunification of the country by force.[51]

text: Despite attempts by both sides to reunify the country, the war perpetuated the division of Korea and led to a permanent alliance between South Korea and the U.S., and a permanent U.S. garrison in the South.[52]

text: Geneva Conference and NNSC[edit]

text: As dictated by the terms of the Korean Armistice, a Geneva Conference was held in 1954 on the Korean question. Despite efforts by many of the nations involved, the conference ended without a declaration for a unified Korea.

text: The Armistice established a Neutral Nations Supervisory Commission (NNSC) which was tasked to monitor the Armistice. Since 1953, members of the Swiss[53] and Swedish[54] Armed Forces have been members of the NNSC stationed near the DMZ.

text: Post-armistice relations[edit]

text: Since the war, Korea has remained divided along the DMZ. North and South have remained in a state of conflict, with the opposing regimes both claiming to be the legitimate government of the whole country. Sporadic negotiations have failed to produce lasting progress towards reunification.[55]


document_title: Atom

question_text: who discovered the atom and in what year

question_tokens: who discovered the atom and in what year

text: Atom

text: History of atomic theory

text: Atoms in philosophy

text: The idea that matter is made up of discrete units is a very old idea, appearing in many ancient cultures such as Greece and India. The word "atom" was coined by the ancient Greek philosophers Leucippus and his pupil Democritus.[1][2] However, these ideas were founded in philosophical and theological reasoning rather than evidence and experimentation. As a result, their views on what atoms look like and how they behave were incorrect. They also could not convince everybody, so atomism was but one of a number of competing theories on the nature of matter. It was not until the 19th century that the idea was embraced and refined by scientists, when the blossoming science of chemistry produced discoveries that only the concept of atoms could explain.

text: First evidence-based theory

text: In the early 1800s, John Dalton used the concept of atoms to explain why elements always react in ratios of small whole numbers (the law of multiple proportions). For instance, there are two types of tin oxide: one is 88.1% tin and 11.9% oxygen and the other is 78.7% tin and 21.3% oxygen (tin(II) oxide and tin dioxide respectively). This means that 100g of tin will combine either with 13.5g or 27g of oxygen. 13.5 and 27 form a ratio of 1:2, a ratio of small whole numbers. This common pattern in chemistry suggested to Dalton that elements react in whole number multiples of discrete units—in other words, atoms. In the case of tin oxides, one tin atom will combine with either one or two oxygen atoms.[3]

text: Dalton also believed atomic theory could explain why water absorbs different gases in different proportions. For example, he found that water absorbs carbon dioxide far better than it absorbs nitrogen.[4] Dalton hypothesized this was due to the differences between the masses and configurations of the gases' respective particles, and carbon dioxide molecules (CO2) are heavier and larger than nitrogen molecules (N2).

text: Brownian motion

text: In 1827, botanist Robert Brown used a microscope to look at dust grains floating in water and discovered that they moved about erratically, a phenomenon that became known as "Brownian motion". This was thought to be caused by water molecules knocking the grains about. In 1905, Albert Einstein proved the reality of these molecules and their motions by producing the first Statistical physics analysis of Brownian motion.[5][6][7] French physicist Jean Perrin used Einstein's work to experimentally determine the mass and dimensions of atoms, thereby conclusively verifying Dalton's atomic theory.[8]

text: Discovery of the electron

text: The physicist J. J. Thomson measured the mass of cathode rays, showing they were made of particles, but were around 1800 times lighter than the lightest atom, hydrogen. Therefore, they were not atoms, but a new particle, the first subatomic particle to be discovered, which he originally called "corpuscle" but was later named electron, after particles postulated by George Johnstone Stoney in 1874. He also showed they were identical to particles given off by photoelectric and radioactive materials.[9] It was quickly recognized that they are the particles that carry electric currents in metal wires, and carry the negative electric charge within atoms. Thomson was given the 1906 Nobel Prize in Physics for this work. Thus he overturned the belief that atoms are the indivisible, ultimate particles of matter.[10] Thomson also incorrectly postulated that the low mass, negatively charged electrons were distributed throughout the atom in a uniform sea of positive charge. This became known as the plum pudding model.

text: Discovery of the nucleus

text: In 1909, Hans Geiger and Ernest Marsden, under the direction of Ernest Rutherford, bombarded a metal foil with alpha particles to observe how they scattered. They expected all the alpha particles to pass straight through with little deflection, because Thomson's model said that the charges in the atom are so diffuse that their electric fields could not affect the alpha particles much. However, Geiger and Marsden spotted alpha particles being deflected by angles greater than 90°, which was supposed to be impossible according to Thomson's model. To explain this, Rutherford proposed that the positive charge of the atom is concentrated in a tiny nucleus at the center of the atom.[11] Rutherford compared his findings to one firing a 15-inch shell at a sheet of tissue paper and it coming back to hit the person who fired it.[12]

text: Discovery of isotopes

text: While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one type of atom at each position on the periodic table.[13] The term isotope was coined by Margaret Todd as a suitable name for different atoms that belong to the same element. J.J. Thomson created a technique for separating atom types through his work on ionized gases, which subsequently led to the discovery of stable isotopes.[14]

text: Bohr model

text: In 1913 the physicist Niels Bohr proposed a model in which the electrons of an atom were assumed to orbit the nucleus but could only do so in a finite set of orbits, and could jump between these orbits only in discrete changes of energy corresponding to absorption or radiation of a photon.[15] This quantization was used to explain why the electrons orbits are stable (given that normally, charges in acceleration, including circular motion, lose kinetic energy which is emitted as electromagnetic radiation, see synchrotron radiation) and why elements absorb and emit electromagnetic radiation in discrete spectra.[16]

text: Later in the same year Henry Moseley provided additional experimental evidence in favor of Niels Bohr's theory. These results refined Ernest Rutherford's and Antonius Van den Broek's model, which proposed that the atom contains in its nucleus a number of positive nuclear charges that is equal to its (atomic) number in the periodic table. Until these experiments, atomic number was not known to be a physical and experimental quantity. That it is equal to the atomic nuclear charge remains the accepted atomic model today.[17]

text: Chemical bonding explained

text: Chemical bonds between atoms were now explained, by Gilbert Newton Lewis in 1916, as the interactions between their constituent electrons.[18] As the chemical properties of the elements were known to largely repeat themselves according to the periodic law,[19] in 1919 the American chemist Irving Langmuir suggested that this could be explained if the electrons in an atom were connected or clustered in some manner. Groups of electrons were thought to occupy a set of electron shells about the nucleus.[20]

text: Further developments in quantum physics

text: The Stern–Gerlach experiment of 1922 provided further evidence of the quantum nature of the atom. When a beam of silver atoms was passed through a specially shaped magnetic field, the beam was split based on the direction of an atom's angular momentum, or spin. As this direction is random, the beam could be expected to spread into a line. Instead, the beam was split into two parts, depending on whether the atomic spin was oriented up or down.[21]

text: In 1924, Louis de Broglie proposed that all particles behave to an extent like waves. In 1926, Erwin Schrödinger used this idea to develop a mathematical model of the atom that described the electrons as three-dimensional waveforms rather than point particles. A consequence of using waveforms to describe particles is that it is mathematically impossible to obtain precise values for both the position and momentum of a particle at a given point in time; this became known as the uncertainty principle, formulated by Werner Heisenberg in 1926. In this concept, for a given accuracy in measuring a position one could only obtain a range of probable values for momentum, and vice versa.[22] This model was able to explain observations of atomic behavior that previous models could not, such as certain structural and spectral patterns of atoms larger than hydrogen. Thus, the planetary model of the atom was discarded in favor of one that described atomic orbital zones around the nucleus where a given electron is most likely to be observed.[23][24]

text: Discovery of the neutron

text: The development of the mass spectrometer allowed the mass of atoms to be measured with increased accuracy. The device uses a magnet to bend the trajectory of a beam of ions, and the amount of deflection is determined by the ratio of an atom's mass to its charge. The chemist Francis William Aston used this instrument to show that isotopes had different masses. The atomic mass of these isotopes varied by integer amounts, called the whole number rule.[25] The explanation for these different isotopes awaited the discovery of the neutron, an uncharged particle with a mass similar to the proton, by the physicist James Chadwick in 1932. Isotopes were then explained as elements with the same number of protons, but different numbers of neutrons within the nucleus.[26]

text: Fission, high-energy physics and condensed matter

text: In 1938, the German chemist Otto Hahn, a student of Rutherford, directed neutrons onto uranium atoms expecting to get transuranium elements. Instead, his chemical experiments showed barium as a product.[27][28] A year later, Lise Meitner and her nephew Otto Frisch verified that Hahn's result were the first experimental nuclear fission.[29][30] In 1944, Hahn received the Nobel prize in chemistry. Despite Hahn's efforts, the contributions of Meitner and Frisch were not recognized.[31]

text: In the 1950s, the development of improved particle accelerators and particle detectors allowed scientists to study the impacts of atoms moving at high energies.[32] Neutrons and protons were found to be hadrons, or composites of smaller particles called quarks. The standard model of particle physics was developed that so far has successfully explained the properties of the nucleus in terms of these sub-atomic particles and the forces that govern their interactions.[33]

text: Structure

text: Subatomic particles

text: Though the word atom originally denoted a particle that cannot be cut into smaller particles, in modern scientific usage the atom is composed of various subatomic particles. The constituent particles of an atom are the electron, the proton and the neutron; all three are fermions. However, the hydrogen-1 atom has no neutrons and the hydron ion has no electrons.

text: The electron is by far the least massive of these particles at 6969911000000000000♠9.11×10−31 kg, with a negative electrical charge and a size that is too small to be measured using available techniques.[34] It is the lightest particle with a positive rest mass measured. Under ordinary conditions, electrons are bound to the positively charged nucleus by the attraction created from opposite electric charges. If an atom has more or fewer electrons than its atomic number, then it becomes respectively negatively or positively charged as a whole; a charged atom is called an ion. Electrons have been known since the late 19th century, mostly thanks to J.J. Thomson; see history of subatomic physics for details.

text: Protons have a positive charge and a mass 1,836 times that of the electron, at 6973167260000000000♠1.6726×10−27 kg. The number of protons in an atom is called its atomic number. Ernest Rutherford (1919) observed that nitrogen under alpha-particle bombardment ejects what appeared to be hydrogen nuclei. By 1920 he had accepted that the hydrogen nucleus is a distinct particle within the atom and named it proton.

text: Neutrons have no electrical charge and have a free mass of 1,839 times the mass of the electron,[35] or 6973169290000000000♠1.6929×10−27 kg, the heaviest of the three constituent particles, but it can be reduced by the nuclear binding energy. Neutrons and protons (collectively known as nucleons) have comparable dimensions—on the order of 6985250000000000000♠2.5×10−15 m—although the 'surface' of these particles is not sharply defined.[36] The neutron was discovered in 1932 by the English physicist James Chadwick.

text: In the Standard Model of physics, electrons are truly elementary particles with no internal structure. However, both protons and neutrons are composite particles composed of elementary particles called quarks. There are two types of quarks in atoms, each having a fractional electric charge. Protons are composed of two up quarks (each with charge +2/3) and one down quark (with a charge of −1/3). Neutrons consist of one up quark and two down quarks. This distinction accounts for the difference in mass and charge between the two particles.[37][38]

text: The quarks are held together by the strong interaction (or strong force), which is mediated by gluons. The protons and neutrons, in turn, are held to each other in the nucleus by the nuclear force, which is a residuum of the strong force that has somewhat different range-properties (see the article on the nuclear force for more). The gluon is a member of the family of gauge bosons, which are elementary particles that mediate physical forces.[37][38]

text: Nucleus

text: All the bound protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to 1.07 3√A fm, where A is the total number of nucleons.[39] This is much smaller than the radius of the atom, which is on the order of 105 fm. The nucleons are bound together by a short-ranged attractive potential called the residual strong force. At distances smaller than 2.5 fm this force is much more powerful than the electrostatic force that causes positively charged protons to repel each other.[40]

text: Atoms of the same element have the same number of protons, called the atomic number. Within a single element, the number of neutrons may vary, determining the isotope of that element. The total number of protons and neutrons determine the nuclide. The number of neutrons relative to the protons determines the stability of the nucleus, with certain isotopes undergoing radioactive decay.[41]

text: The proton, the electron, and the neutron are classified as fermions. Fermions obey the Pauli exclusion principle which prohibits identical fermions, such as multiple protons, from occupying the same quantum state at the same time. Thus, every proton in the nucleus must occupy a quantum state different from all other protons, and the same applies to all neutrons of the nucleus and to all electrons of the electron cloud. However, a proton and a neutron are allowed to occupy the same quantum state.[42]

text: For atoms with low atomic numbers, a nucleus that has more neutrons than protons tends to drop to a lower energy state through radioactive decay so that the neutron–proton ratio is closer to one. However, as the atomic number increases, a higher proportion of neutrons is required to offset the mutual repulsion of the protons. Thus, there are no stable nuclei with equal proton and neutron numbers above atomic number Z = 20 (calcium) and as Z increases, the neutron–proton ratio of stable isotopes increases.[42] The stable isotope with the highest proton–neutron ratio is lead-208 (about 1.5).

text: The number of protons and neutrons in the atomic nucleus can be modified, although this can require very high energies because of the strong force. Nuclear fusion occurs when multiple atomic particles join to form a heavier nucleus, such as through the energetic collision of two nuclei. For example, at the core of the Sun protons require energies of 3–10 keV to overcome their mutual repulsion—the coulomb barrier—and fuse together into a single nucleus.[43] Nuclear fission is the opposite process, causing a nucleus to split into two smaller nuclei—usually through radioactive decay. The nucleus can also be modified through bombardment by high energy subatomic particles or photons. If this modifies the number of protons in a nucleus, the atom changes to a different chemical element.[44][45]

text: If the mass of the nucleus following a fusion reaction is less than the sum of the masses of the separate particles, then the difference between these two values can be emitted as a type of usable energy (such as a gamma ray, or the kinetic energy of a beta particle), as described by Albert Einstein's mass–energy equivalence formula, E = mc2, where m is the mass loss and c is the speed of light. This deficit is part of the binding energy of the new nucleus, and it is the non-recoverable loss of the energy that causes the fused particles to remain together in a state that requires this energy to separate.[46]

text: The fusion of two nuclei that create larger nuclei with lower atomic numbers than iron and nickel—a total nucleon number of about 60—is usually an exothermic process that releases more energy than is required to bring them together.[47] It is this energy-releasing process that makes nuclear fusion in stars a self-sustaining reaction. For heavier nuclei, the binding energy per nucleon in the nucleus begins to decrease. That means fusion processes producing nuclei that have atomic numbers higher than about 26, and atomic masses higher than about 60, is an endothermic process. These more massive nuclei can not undergo an energy-producing fusion reaction that can sustain the hydrostatic equilibrium of a star.[42]

text: Electron cloud

text: The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force. This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed for the electron to escape. The closer an electron is to the nucleus, the greater the attractive force. Hence electrons bound near the center of the potential well require more energy to escape than those at greater separations.

text: Electrons, like other particles, have properties of both a particle and a wave. The electron cloud is a region inside the potential well where each electron forms a type of three-dimensional standing wave—a wave form that does not move relative to the nucleus. This behavior is defined by an atomic orbital, a mathematical function that characterises the probability that an electron appears to be at a particular location when its position is measured.[48] Only a discrete (or quantized) set of these orbitals exist around the nucleus, as other possible wave patterns rapidly decay into a more stable form.[49] Orbitals can have one or more ring or node structures, and differ from each other in size, shape and orientation.[50]

text: Each atomic orbital corresponds to a particular energy level of the electron. The electron can change its state to a higher energy level by absorbing a photon with sufficient energy to boost it into the new quantum state. Likewise, through spontaneous emission, an electron in a higher energy state can drop to a lower energy state while radiating the excess energy as a photon. These characteristic energy values, defined by the differences in the energies of the quantum states, are responsible for atomic spectral lines.[49]

text: The amount of energy needed to remove or add an electron—the electron binding energy—is far less than the binding energy of nucleons. For example, it requires only 13.6 eV to strip a ground-state electron from a hydrogen atom,[51] compared to 2.23 million eV for splitting a deuterium nucleus.[52] Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms that have either a deficit or a surplus of electrons are called ions. Electrons that are farthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism, atoms are able to bond into molecules and other types of chemical compounds like ionic and covalent network crystals.[53]

text: Properties

text: Nuclear properties

text: By definition, any two atoms with an identical number of protons in their nuclei belong to the same chemical element. Atoms with equal numbers of protons but a different number of neutrons are different isotopes of the same element. For example, all hydrogen atoms admit exactly one proton, but isotopes exist with no neutrons (hydrogen-1, by far the most common form,[54] also called protium), one neutron (deuterium), two neutrons (tritium) and more than two neutrons. The known elements form a set of atomic numbers, from the single proton element hydrogen up to the 118-proton element oganesson.[55] All known isotopes of elements with atomic numbers greater than 82 are radioactive, although the radioactivity of element 83 (bismuth) is so slight as to be practically negligible.[56][57]

text: About 339 nuclides occur naturally on Earth,[58] of which 254 (about 75%) have not been observed to decay, and are referred to as "stable isotopes". However, only 90 of these nuclides are stable to all decay, even in theory. Another 164 (bringing the total to 254) have not been observed to decay, even though in theory it is energetically possible. These are also formally classified as "stable". An additional 34 radioactive nuclides have half-lives longer than 80 million years, and are long-lived enough to be present from the birth of the solar system. This collection of 288 nuclides are known as primordial nuclides. Finally, an additional 51 short-lived nuclides are known to occur naturally, as daughter products of primordial nuclide decay (such as radium from uranium), or else as products of natural energetic processes on Earth, such as cosmic ray bombardment (for example, carbon-14).[59][note 1]

text: For 80 of the chemical elements, at least one stable isotope exists. As a rule, there is only a handful of stable isotopes for each of these elements, the average being 3.2 stable isotopes per element. Twenty-six elements have only a single stable isotope, while the largest number of stable isotopes observed for any element is ten, for the element tin. Elements 43, 61, and all elements numbered 83 or higher have no stable isotopes.[60][page needed]

text: Stability of isotopes is affected by the ratio of protons to neutrons, and also by the presence of certain "magic numbers" of neutrons or protons that represent closed and filled quantum shells. These quantum shells correspond to a set of energy levels within the shell model of the nucleus; filled shells, such as the filled shell of 50 protons for tin, confers unusual stability on the nuclide. Of the 254 known stable nuclides, only four have both an odd number of protons and odd number of neutrons: hydrogen-2 (deuterium), lithium-6, boron-10 and nitrogen-14. Also, only four naturally occurring, radioactive odd–odd nuclides have a half-life over a billion years: potassium-40, vanadium-50, lanthanum-138 and tantalum-180m. Most odd–odd nuclei are highly unstable with respect to beta decay, because the decay products are even–even, and are therefore more strongly bound, due to nuclear pairing effects.[60][page needed]

text: Mass

text: The large majority of an atom's mass comes from the protons and neutrons that make it up. The total number of these particles (called "nucleons") in a given atom is called the mass number. It is a positive integer and dimensionless (instead of having dimension of mass), because it expresses a count. An example of use of a mass number is "carbon-12," which has 12 nucleons (six protons and six neutrons).

text: The actual mass of an atom at rest is often expressed using the unified atomic mass unit (u), also called dalton (Da). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately 6973166000000000000♠1.66×10−27 kg.[61] Hydrogen-1 (the lightest isotope of hydrogen which is also the nuclide with the lowest mass) has an atomic weight of 1.007825 u.[62] The value of this number is called the atomic mass. A given atom has an atomic mass approximately equal (within 1%) to its mass number times the atomic mass unit (for example the mass of a nitrogen-14 is roughly 14 u). However, this number will not be exactly an integer except in the case of carbon-12 (see below).[63] The heaviest stable atom is lead-208,[56] with a mass of 7002207976652100000♠207.9766521 u.[64]

text: As even the most massive atoms are far too light to work with directly, chemists instead use the unit of moles. One mole of atoms of any element always has the same number of atoms (about 7023602200000000000♠6.022×1023). This number was chosen so that if an element has an atomic mass of 1 u, a mole of atoms of that element has a mass close to one gram. Because of the definition of the unified atomic mass unit, each carbon-12 atom has an atomic mass of exactly 12 u, and so a mole of carbon-12 atoms weighs exactly 0.012 kg.[61]

text: Shape and size

text: Atoms lack a well-defined outer boundary, so their dimensions are usually described in terms of an atomic radius. This is a measure of the distance out to which the electron cloud extends from the nucleus.[65] However, this assumes the atom to exhibit a spherical shape, which is only obeyed for atoms in vacuum or free space. Atomic radii may be derived from the distances between two nuclei when the two atoms are joined in a chemical bond. The radius varies with the location of an atom on the atomic chart, the type of chemical bond, the number of neighboring atoms (coordination number) and a quantum mechanical property known as spin.[66] On the periodic table of the elements, atom size tends to increase when moving down columns, but decrease when moving across rows (left to right).[67] Consequently, the smallest atom is helium with a radius of 32 pm, while one of the largest is caesium at 225 pm.[68]

text: When subjected to external forces, like electrical fields, the shape of an atom may deviate from spherical symmetry. The deformation depends on the field magnitude and the orbital type of outer shell electrons, as shown by group-theoretical considerations. Aspherical deviations might be elicited for instance in crystals, where large crystal-electrical fields may occur at low-symmetry lattice sites.[69][70] Significant ellipsoidal deformations have been shown to occur for sulfur ions[71] and chalcogen ions[72] in pyrite-type compounds.

text: Atomic dimensions are thousands of times smaller than the wavelengths of light (400–700 nm) so they cannot be viewed using an optical microscope. However, individual atoms can be observed using a scanning tunneling microscope. To visualize the minuteness of the atom, consider that a typical human hair is about 1 million carbon atoms in width.[73] A single drop of water contains about 2 sextillion (7021200000000000000♠2×1021) atoms of oxygen, and twice the number of hydrogen atoms.[74] A single carat diamond with a mass of 6996200000000000000♠2×10−4 kg contains about 10 sextillion (1022) atoms of carbon.[note 2] If an apple were magnified to the size of the Earth, then the atoms in the apple would be approximately the size of the original apple.[75]

text: Radioactive decay

text: Every element has one or more isotopes that have unstable nuclei that are subject to radioactive decay, causing the nucleus to emit particles or electromagnetic radiation. Radioactivity can occur when the radius of a nucleus is large compared with the radius of the strong force, which only acts over distances on the order of 1 fm.[76]

text: The most common forms of radioactive decay are:[77][78]

text:
Alpha decay: this process is caused when the nucleus emits an alpha particle, which is a helium nucleus consisting of two protons and two neutrons. The result of the emission is a new element with a lower atomic number.
Beta decay (and electron capture): these processes are regulated by the weak force, and result from a transformation of a neutron into a proton, or a proton into a neutron. The neutron to proton transition is accompanied by the emission of an electron and an antineutrino, while proton to neutron transition (except in electron capture) causes the emission of a positron and a neutrino. The electron or positron emissions are called beta particles. Beta decay either increases or decreases the atomic number of the nucleus by one. Electron capture is more common than positron emission, because it requires less energy. In this type of decay, an electron is absorbed by the nucleus, rather than a positron emitted from the nucleus. A neutrino is still emitted in this process, and a proton changes to a neutron.
Gamma decay: this process results from a change in the energy level of the nucleus to a lower state, resulting in the emission of electromagnetic radiation. The excited state of a nucleus which results in gamma emission usually occurs following the emission of an alpha or a beta particle. Thus, gamma decay usually follows alpha or beta decay.

text: Other more rare types of radioactive decay include ejection of neutrons or protons or clusters of nucleons from a nucleus, or more than one beta particle. An analog of gamma emission which allows excited nuclei to lose energy in a different way, is internal conversion— a process that produces high-speed electrons that are not beta rays, followed by production of high-energy photons that are not gamma rays. A few large nuclei explode into two or more charged fragments of varying masses plus several neutrons, in a decay called spontaneous nuclear fission.

text: Each radioactive isotope has a characteristic decay time period—the half-life—that is determined by the amount of time needed for half of a sample to decay. This is an exponential decay process that steadily decreases the proportion of the remaining isotope by 50% every half-life. Hence after two half-lives have passed only 25% of the isotope is present, and so forth.[76]

text: Magnetic moment

text: Elementary particles possess an intrinsic quantum mechanical property known as spin. This is analogous to the angular momentum of an object that is spinning around its center of mass, although strictly speaking these particles are believed to be point-like and cannot be said to be rotating. Spin is measured in units of the reduced Planck constant (ħ), with electrons, protons and neutrons all having spin ½ ħ, or "spin-½". In an atom, electrons in motion around the nucleus possess orbital angular momentum in addition to their spin, while the nucleus itself possesses angular momentum due to its nuclear spin.[79]

text: The magnetic field produced by an atom—its magnetic moment—is determined by these various forms of angular momentum, just as a rotating charged object classically produces a magnetic field. However, the most dominant contribution comes from electron spin. Due to the nature of electrons to obey the Pauli exclusion principle, in which no two electrons may be found in the same quantum state, bound electrons pair up with each other, with one member of each pair in a spin up state and the other in the opposite, spin down state. Thus these spins cancel each other out, reducing the total magnetic dipole moment to zero in some atoms with even number of electrons.[80]

text: In ferromagnetic elements such as iron, cobalt and nickel, an odd number of electrons leads to an unpaired electron and a net overall magnetic moment. The orbitals of neighboring atoms overlap and a lower energy state is achieved when the spins of unpaired electrons are aligned with each other, a spontaneous process known as an exchange interaction. When the magnetic moments of ferromagnetic atoms are lined up, the material can produce a measurable macroscopic field. Paramagnetic materials have atoms with magnetic moments that line up in random directions when no magnetic field is present, but the magnetic moments of the individual atoms line up in the presence of a field.[80][81]

text: The nucleus of an atom will have no spin when it has even numbers of both neutrons and protons, but for other cases of odd numbers, the nucleus may have a spin. Normally nuclei with spin are aligned in random directions because of thermal equilibrium. However, for certain elements (such as xenon-129) it is possible to polarize a significant proportion of the nuclear spin states so that they are aligned in the same direction—a condition called hyperpolarization. This has important applications in magnetic resonance imaging.[82][83]

text: Energy levels

text: The potential energy of an electron in an atom is negative, its dependence of its position reaches the minimum (the most absolute value) inside the nucleus, and vanishes when the distance from the nucleus goes to infinity, roughly in an inverse proportion to the distance. In the quantum-mechanical model, a bound electron can only occupy a set of states centered on the nucleus, and each state corresponds to a specific energy level; see time-independent Schrödinger equation for theoretical explanation. An energy level can be measured by the amount of energy needed to unbind the electron from the atom, and is usually given in units of electronvolts (eV). The lowest energy state of a bound electron is called the ground state, i.e. stationary state, while an electron transition to a higher level results in an excited state.[84] The electron's energy raises when n increases because the (average) distance to the nucleus increases. Dependence of the energy on ℓ is caused not by electrostatic potential of the nucleus, but by interaction between electrons.

text: For an electron to transition between two different states, e.g. grounded state to first excited level (ionization), it must absorb or emit a photon at an energy matching the difference in the potential energy of those levels, according to Niels Bohr model, what can be precisely calculated by the Schrödinger equation. Electrons jump between orbitals in a particle-like fashion. For example, if a single photon strikes the electrons, only a single electron changes states in response to the photon; see Electron properties.

text: The energy of an emitted photon is proportional to its frequency, so these specific energy levels appear as distinct bands in the electromagnetic spectrum.[85] Each element has a characteristic spectrum that can depend on the nuclear charge, subshells filled by electrons, the electromagnetic interactions between the electrons and other factors.[86]

text: When a continuous spectrum of energy is passed through a gas or plasma, some of the photons are absorbed by atoms, causing electrons to change their energy level. Those excited electrons that remain bound to their atom spontaneously emit this energy as a photon, traveling in a random direction, and so drop back to lower energy levels. Thus the atoms behave like a filter that forms a series of dark absorption bands in the energy output. (An observer viewing the atoms from a view that does not include the continuous spectrum in the background, instead sees a series of emission lines from the photons emitted by the atoms.) Spectroscopic measurements of the strength and width of atomic spectral lines allow the composition and physical properties of a substance to be determined.[87]

text: Close examination of the spectral lines reveals that some display a fine structure splitting. This occurs because of spin–orbit coupling, which is an interaction between the spin and motion of the outermost electron.[88] When an atom is in an external magnetic field, spectral lines become split into three or more components; a phenomenon called the Zeeman effect. This is caused by the interaction of the magnetic field with the magnetic moment of the atom and its electrons. Some atoms can have multiple electron configurations with the same energy level, which thus appear as a single spectral line. The interaction of the magnetic field with the atom shifts these electron configurations to slightly different energy levels, resulting in multiple spectral lines.[89] The presence of an external electric field can cause a comparable splitting and shifting of spectral lines by modifying the electron energy levels, a phenomenon called the Stark effect.[90]

text: If a bound electron is in an excited state, an interacting photon with the proper energy can cause stimulated emission of a photon with a matching energy level. For this to occur, the electron must drop to a lower energy state that has an energy difference matching the energy of the interacting photon. The emitted photon and the interacting photon then move off in parallel and with matching phases. That is, the wave patterns of the two photons are synchronized. This physical property is used to make lasers, which can emit a coherent beam of light energy in a narrow frequency band.[91]

text: Valence and bonding behavior

text: Valency is the combining power of an element. It is equal to number of hydrogen atoms that atom can combine or displace in forming compounds.[92] The outermost electron shell of an atom in its uncombined state is known as the valence shell, and the electrons in that shell are called valence electrons. The number of valence electrons determines the bonding behavior with other atoms. Atoms tend to chemically react with each other in a manner that fills (or empties) their outer valence shells.[93] For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound sodium chloride and other chemical ionic salts. However, many elements display multiple valences, or tendencies to share differing numbers of electrons in different compounds. Thus, chemical bonding between these elements takes many forms of electron-sharing that are more than simple electron transfers. Examples include the element carbon and the organic compounds.[94]

text: The chemical elements are often displayed in a periodic table that is laid out to display recurring chemical properties, and elements with the same number of valence electrons form a group that is aligned in the same column of the table. (The horizontal rows correspond to the filling of a quantum shell of electrons.) The elements at the far right of the table have their outer shell completely filled with electrons, which results in chemically inert elements known as the noble gases.[95][96]

text: States

text: Quantities of atoms are found in different states of matter that depend on the physical conditions, such as temperature and pressure. By varying the conditions, materials can transition between solids, liquids, gases and plasmas.[97] Within a state, a material can also exist in different allotropes. An example of this is solid carbon, which can exist as graphite or diamond.[98] Gaseous allotropes exist as well, such as dioxygen and ozone.

text: At temperatures close to absolute zero, atoms can form a Bose–Einstein condensate, at which point quantum mechanical effects, which are normally only observed at the atomic scale, become apparent on a macroscopic scale.[99][100] This super-cooled collection of atoms then behaves as a single super atom, which may allow fundamental checks of quantum mechanical behavior.[101]

text: Identification

text: The scanning tunneling microscope is a device for viewing surfaces at the atomic level. It uses the quantum tunneling phenomenon, which allows particles to pass through a barrier that would normally be insurmountable. Electrons tunnel through the vacuum between two planar metal electrodes, on each of which is an adsorbed atom, providing a tunneling-current density that can be measured. Scanning one atom (taken as the tip) as it moves past the other (the sample) permits plotting of tip displacement versus lateral separation for a constant current. The calculation shows the extent to which scanning-tunneling-microscope images of an individual atom are visible. It confirms that for low bias, the microscope images the space-averaged dimensions of the electron orbitals across closely packed energy levels—the Fermi level local density of states.[102][103]

text: An atom can be ionized by removing one of its electrons. The electric charge causes the trajectory of an atom to bend when it passes through a magnetic field. The radius by which the trajectory of a moving ion is turned by the magnetic field is determined by the mass of the atom. The mass spectrometer uses this principle to measure the mass-to-charge ratio of ions. If a sample contains multiple isotopes, the mass spectrometer can determine the proportion of each isotope in the sample by measuring the intensity of the different beams of ions. Techniques to vaporize atoms include inductively coupled plasma atomic emission spectroscopy and inductively coupled plasma mass spectrometry, both of which use a plasma to vaporize samples for analysis.[104]

text: A more area-selective method is electron energy loss spectroscopy, which measures the energy loss of an electron beam within a transmission electron microscope when it interacts with a portion of a sample. The atom-probe tomograph has sub-nanometer resolution in 3-D and can chemically identify individual atoms using time-of-flight mass spectrometry.[105]

text: Spectra of excited states can be used to analyze the atomic composition of distant stars. Specific light wavelengths contained in the observed light from stars can be separated out and related to the quantized transitions in free gas atoms. These colors can be replicated using a gas-discharge lamp containing the same element.[106] Helium was discovered in this way in the spectrum of the Sun 23 years before it was found on Earth.[107]

text: Origin and current state

text: Atoms form about 4% of the total energy density of the observable Universe, with an average density of about 0.25 atoms/m3.[108] Within a galaxy such as the Milky Way, atoms have a much higher concentration, with the density of matter in the interstellar medium (ISM) ranging from 105 to 109 atoms/m3.[109] The Sun is believed to be inside the Local Bubble, a region of highly ionized gas, so the density in the solar neighborhood is only about 103 atoms/m3.[110] Stars form from dense clouds in the ISM, and the evolutionary processes of stars result in the steady enrichment of the ISM with elements more massive than hydrogen and helium. Up to 95% of the Milky Way's atoms are concentrated inside stars and the total mass of atoms forms about 10% of the mass of the galaxy.[111] (The remainder of the mass is an unknown dark matter.)[112]

text: Formation

text: Electrons are thought to exist in the Universe since early stages of the Big Bang. Atomic nuclei forms in nucleosynthesis reactions. In about three minutes Big Bang nucleosynthesis produced most of the helium, lithium, and deuterium in the Universe, and perhaps some of the beryllium and boron.[113][114][115]

text: Ubiquitousness and stability of atoms relies on their binding energy, which means that an atom has a lower energy than an unbound system of the nucleus and electrons. Where the temperature is much higher than ionization potential, the matter exists in the form of plasma—a gas of positively charged ions (possibly, bare nuclei) and electrons. When the temperature drops below the ionization potential, atoms become statistically favorable. Atoms (complete with bound electrons) became to dominate over charged particles 380,000 years after the Big Bang—an epoch called recombination, when the expanding Universe cooled enough to allow electrons to become attached to nuclei.[116]

text: Since the Big Bang, which produced no carbon or heavier elements, atomic nuclei have been combined in stars through the process of nuclear fusion to produce more of the element helium, and (via the triple alpha process) the sequence of elements from carbon up to iron;[117] see stellar nucleosynthesis for details.

text: Isotopes such as lithium-6, as well as some beryllium and boron are generated in space through cosmic ray spallation.[118] This occurs when a high-energy proton strikes an atomic nucleus, causing large numbers of nucleons to be ejected.

text: Elements heavier than iron were produced in supernovae through the r-process and in AGB stars through the s-process, both of which involve the capture of neutrons by atomic nuclei.[119] Elements such as lead formed largely through the radioactive decay of heavier elements.[120]

text: Earth

text: Most of the atoms that make up the Earth and its inhabitants were present in their current form in the nebula that collapsed out of a molecular cloud to form the Solar System. The rest are the result of radioactive decay, and their relative proportion can be used to determine the age of the Earth through radiometric dating.[121][122] Most of the helium in the crust of the Earth (about 99% of the helium from gas wells, as shown by its lower abundance of helium-3) is a product of alpha decay.[123]

text: There are a few trace atoms on Earth that were not present at the beginning (i.e., not "primordial"), nor are results of radioactive decay. Carbon-14 is continuously generated by cosmic rays in the atmosphere.[124] Some atoms on Earth have been artificially generated either deliberately or as by-products of nuclear reactors or explosions.[125][126] Of the transuranic elements—those with atomic numbers greater than 92—only plutonium and neptunium occur naturally on Earth.[127][128] Transuranic elements have radioactive lifetimes shorter than the current age of the Earth[129] and thus identifiable quantities of these elements have long since decayed, with the exception of traces of plutonium-244 possibly deposited by cosmic dust.[130] Natural deposits of plutonium and neptunium are produced by neutron capture in uranium ore.[131]

text: The Earth contains approximately 7050133000000000000♠1.33×1050 atoms.[132] Although small numbers of independent atoms of noble gases exist, such as argon, neon, and helium, 99% of the atmosphere is bound in the form of molecules, including carbon dioxide and diatomic oxygen and nitrogen. At the surface of the Earth, an overwhelming majority of atoms combine to form various compounds, including water, salt, silicates and oxides. Atoms can also combine to create materials that do not consist of discrete molecules, including crystals and liquid or solid metals.[133][134] This atomic matter forms networked arrangements that lack the particular type of small-scale interrupted order associated with molecular matter.[135]

text: Rare and theoretical forms

text: Superheavy elements

text: While isotopes with atomic numbers higher than lead (82) are known to be radioactive, an "island of stability" has been proposed for some elements with atomic numbers above 103. These superheavy elements may have a nucleus that is relatively stable against radioactive decay.[136] The most likely candidate for a stable superheavy atom, unbihexium, has 126 protons and 184 neutrons.[137]

text: Exotic matter

text: Each particle of matter has a corresponding antimatter particle with the opposite electrical charge. Thus, the positron is a positively charged antielectron and the antiproton is a negatively charged equivalent of a proton. When a matter and corresponding antimatter particle meet, they annihilate each other. Because of this, along with an imbalance between the number of matter and antimatter particles, the latter are rare in the universe. The first causes of this imbalance are not yet fully understood, although theories of baryogenesis may offer an explanation. As a result, no antimatter atoms have been discovered in nature.[138][139] However, in 1996 the antimatter counterpart of the hydrogen atom (antihydrogen) was synthesized at the CERN laboratory in Geneva.[140][141]

text: Other exotic atoms have been created by replacing one of the protons, neutrons or electrons with other particles that have the same charge. For example, an electron can be replaced by a more massive muon, forming a muonic atom. These types of atoms can be used to test the fundamental predictions of physics.[142][143][144]