document_title: The Six Million Dollar Man

question_text: how fast can the six million dollar man run

text: The Six Million Dollar Man

text: Plot[edit]

text: This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (April 2010) (Learn how and when to remove this template message)

text: Original series[edit]

text: When NASA astronaut Steve Austin is severely injured in the crash of an experimental lifting body aircraft, he is "rebuilt" in an operation that costs six million dollars (equivalent to $33 million in 2017). His right arm, both legs and the left eye are replaced with "bionic" implants that enhance his strength, speed and vision far above human norms: he can run at speeds of over 60 mph (97 km/h), and his eye has a 20:1 zoom lens and infrared capabilities, while his bionic limbs all have the equivalent power of a bulldozer. He uses his enhanced abilities to work for the OSI (Office of Scientific Intelligence) as a secret agent.

text: Caidin's novel Cyborg was a best-seller when it was published in 1972.  He followed it up with three sequels, Operation Nuke, High Crystal, and Cyborg IV, respectively about a black market in nuclear weapons, a Chariots of the Gods? scenario, and fusing Austin's bionic hardware to a spaceplane.

text: In March 1973, Cyborg was loosely adapted as a made-for-TV movie titled The Six Million Dollar Man starring Majors as Austin. The producers first choice was Monte Markham.[citation needed] (When re-edited for the later series, it was re-titled "The Moon and the Desert, Parts I and II".) The adaptation was done by writer Howard Rodman, working under the pseudonym of Henri Simoun. The film, which was nominated for a Hugo Award, modified Caidin's plot, and notably made Austin a civilian astronaut rather than a colonel in the United States Air Force. Absent were some of the standard features of the later series: the electronic sound effects, the slow-motion running, and the character of Oscar Goldman. Instead, another character named Oliver Spencer, played by Darren McGavin, was Austin's supervisor, of an organization here called the OSO. (In the novels, "OSO" stood for Office of Special Operations. The CIA did have an Office of Scientific Intelligence in the 1970s.) The lead scientist involved in implanting Austin's bionic hardware, Dr. Rudy Wells, was played in the pilot by Martin Balsam, then on an occasional basis in the series by Alan Oppenheimer, and, finally, as a series regular, by Martin E. Brooks. Austin did not use the enhanced capabilities of his bionic eye during the first TV movie.

text: The first movie was a major ratings success and was followed by two more made-for-TV movies in October and November 1973 as part of ABC's rotating "Suspense Theater" series. The first was titled The Six Million Dollar Man: "Wine, Women and War", and the second was titled The Six Million Dollar Man: "The Solid Gold Kidnapping". The first of these two bore strong resemblances to Caidin's second Cyborg novel, Operation Nuke; the second, however, was an original story. This was followed in January 1974 by the debut of The Six Million Dollar Man as a weekly hour-long series. The last two movies, produced by Glen A. Larson, notably introduced a James Bond flavor to the series and reinstated Austin's status from the novels as an Air Force colonel; the hour-long series, produced by Harve Bennett, dispensed with the James Bond-gloss of the movies, and portrayed a more down-to-earth Austin. (Majors said of Austin, "[He] hates...the whole idea of spying. He finds it repugnant, degrading. If he's a James Bond, he's the most reluctant one we've ever had.")[citation needed]

text: The show was very popular during its run and introduced several pop culture elements of the 1970s, such as the show's opening catchphrase ("We can rebuild him; we have the technology," voiced over by Richard Anderson in his role of Oscar Goldman), the slow motion action sequences, and the accompanying "electronic" sound effects. The slow motion action sequences were originally referred to as "Kung Fu slow motion" in popular culture (due to its usage in the 1970s martial arts television series).

text: In 1975, a two-part episode entitled "The Bionic Woman", written for television by Kenneth Johnson, introduced the lead character Jaime Sommers (played by Lindsay Wagner), a professional tennis player who rekindled an old romance with Austin, only to experience a parachuting accident that resulted in her being given bionic parts similar to Austin. Ultimately, her body "rejected" her bionic hardware and she died. The character was very popular, however, and the following season it was revealed that she had actually survived, having been saved by an experimental cryogenic procedure, and she was given her own spin-off series, The Bionic Woman.  This spin-off ran until 1978 when both it and The Six Million Dollar Man were simultaneously cancelled, though the two series were on different networks when their final seasons aired.

text: Television movie reunions[edit]

text: Steve Austin and Jaime Sommers returned in three subsequent made-for-television movies: The Return of the Six Million Dollar Man and the Bionic Woman (1987), Bionic Showdown: The Six Million Dollar Man and the Bionic Woman (1989) which featured Sandra Bullock in an early role as a new bionic woman; and Bionic Ever After? (1994) in which Austin and Sommers finally marry. Majors reprised the role of Steve Austin in all three productions, which also featured Richard Anderson and Martin E. Brooks, and Lindsay Wagner reprising the role of Jaime Sommers. The reunion films addressed the partial amnesia Sommers had suffered during the original series, and all three featured Majors' son, Lee Majors II, as OSI agent Jim Castillian. The first two movies were written in the anticipation of creating new bionic characters in their own series, but nothing further was seen of the new characters introduced in those produced. The third TV movie was intended as a finale.

text: Cast[edit]

text:
Steve Austin (played by Lee Majors), the lead character
Oscar Goldman (played by Richard Anderson), Director of the OSI
Dr. Rudy Wells (played by Martin Balsam in pilot; Alan Oppenheimer, seasons 1 & 2; Martin E. Brooks, seasons 3–5, as well as on The Bionic Woman and in three movies), Austin's physician and primary overseer of the medical aspects of bionic technology
Jaime Sommers (played by Lindsay Wagner—recurring)
Peggy Callahan (played by Jennifer Darling—recurring), secretary to Oscar Goldman
Oliver Spencer (played by Darren McGavin), Director of the OSO in the pilot

text: Production[edit]

text: Opening sequence[edit]

text: The dialogue spoken by actor Lee Majors during the opening credits is based upon communication prior to the M2-F2 crash that occurred on May 10, 1967: ("Flight com, I can't hold her! She's breaking up! She's break—"). Test pilot Bruce Peterson's lifting body aircraft hit the ground at approximately 250 mph (402 km/h) and tumbled six times.[3]  But Peterson survived what appeared to be a fatal accident, though he later lost an eye due to infection.[n 2] In the episode "The Deadly Replay", Oscar Goldman refers to the lifting body aircraft in which Austin crashed as the HL-10, stating "We've rebuilt the HL-10." In the 1987 TV film The Return of the Six Million Dollar Man and the Bionic Woman, Austin refers to the craft as the "M3-F5", which was the name used for the aircraft that crashed in the original Cyborg novel.)

text: In the opening sequence, a narrator (series producer Harve Bennett) identifies the protagonist, "Steve Austin, astronaut. A man barely alive." Richard Anderson, in character as Oscar Goldman, then intones off-camera, "Gentlemen, we can rebuild him. We have the technology. We have the capability to make the world's first bionic man. Steve Austin will be that man. Better than he was before. Better...stronger...faster." During the first season, beginning with "Population: Zero", Anderson, as Goldman, intoned more simply, "We can rebuild him. We have the technology. We can make him better than he was. Better...stronger...faster." During the operation, when he is having his bionics fitted, a list of items and numbers is displayed and lists his powerplant as "atomic".

text: Theme music[edit]

text: Dusty Springfield, backed by Ron "Escalade" Piscina, sang the theme song written by Glen A. Larson[4] which was used in the opening and closing credits for the Wine, Women & War and The Solid Gold Kidnapping telefilms. The song was also used in the promotion of the series, but when the weekly series began the song was replaced by the instrumental theme by Oliver Nelson. The first regular episode, "Population: Zero", introduced a new element to the opening sequence: a voiceover by Oscar Goldman stating the rationale behind creating a bionic man. The first season narration was shorter than that used in the second and subsequent seasons.

text: Steve Austin's bionics[edit]

text: This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2015) (Learn how and when to remove this template message)

text: To maintain the show's plausibility, producer Kenneth Johnson set very specific limits on Steve Austin's abilities. He elaborated, "When you’re dealing with the area of fantasy, if you say, ‘Well, they’re bionic so they can do whatever they want,’ then it gets out of hand, so you’ve got to have really, really tight rules. [Steve and Jaime] can jump up two stories but not three. They can jump down three stories but not four."[5] Austin's superhuman enhancements are:

text: A bionic left eye:

text: Bionic legs:

text: A bionic right arm:

text: The implants have a major flaw in that extreme cold interferes with their functions and can disable them given sufficient exposure. However, when Austin returns to a warmer temperature, the implants quickly regain full functionality. The first season also established that Austin's bionics malfunction in the micro-gravity of space, though Austin's bionics are later modified to rectify this. The bionic eye is vulnerable to ultrasonic attack, resulting in blindness and dizziness. It is not explained how Austin's organic body is able to withstand the stress of either bionic hardware weight or performance of superhuman feats.

text: To indicate to viewers that Austin was running or using his bionic arm, sequences with him using these abilities were presented in slow-motion and accompanied by an electronic "dit dit dit dit" sound effect.[5] (This characteristic sound effect was actually first used in season 1 episode 4, "Day of the Robot", not during use of Austin's bionics but with the robotic clone of Major Fred Sloan, played by actor John Saxon, during the final fight scene.) When the bionic eye was used, the camera would zoom in on Austin's face, followed by an extreme close-up of his eye; his point of view usually included a crosshair motif accompanied by a beeping sound-effect. In early episodes, different ways of presenting Austin's powers were tested, including a heartbeat sound effect that predated the electronic sound, and in the three original made-for-TV movies, no sound effects or slow-motion were used, with Austin's actions shown at normal speed (except for his running, which utilized trick photography); the slow-motion portrayal was introduced with the first hour-long episode, "Population: Zero."

text: Episodes[edit]

text: The series consists of three TV-movies, five seasons of episodes, and three more TV-movies.

text:
Season

Episodes

Originally aired

First aired

Last aired

Television movies

March 7, 1973

November 17, 1973

1

13

January 18, 1974

April 26, 1974

2

22

September 13, 1974

April 27, 1975

3

21

September 14, 1975

March 7, 1976

4

22

September 19, 1976

March 15, 1977

5

21

September 11, 1977

March 6, 1978

Television movies

May 17, 1987

November 29, 1994

text: Novels[edit]

text: Martin Caidin wrote four novels featuring his original version of Steve Austin beginning in 1972 with Cyborg. Although several other writers such as Mike Jahn would later write a number of novelizations based upon the TV series, in most cases these writers chose to base their character upon the literary version of Austin rather than the TV show version. As a result, several of the novelizations have entire scenes and in one case an ending that differed from the original episodes, as the cold-blooded killer of Caidin's novels handled things somewhat differently from his non-killing TV counterpart. For example, the Jahn book International Incidents, an adaptation of the episode "Love Song for Tanya", ends with Austin using the poison dart gun in his bionic hand to kill an enemy agent; since the TV version of the character lacked this weapon, the villain was simply captured in the episode as broadcast.

text: Original novels[edit]

text: (all by Martin Caidin)

text:
Cyborg (1972)
Operation Nuke (1973)
High Crystal (1974)
Cyborg IV (1975)

text: (Of the above, only Cyborg was adapted for television.)

text: Novelizations[edit]

text:
Wine, Women and War – Mike Jahn
Solid Gold Kidnapping – Evan Richards
Pilot Error – Jay Barbree
The Rescue of Athena One – Jahn
The Secret of Bigfoot Pass (UK title, The Secret of Bigfoot) – Jahn
International Incidents – Jahn (this volume adapted several episodes into one interconnected storyline)

text: Other adaptations[edit]

text: Comics[edit]

text: Charlton Comics published both a color comic book and a black and white, illustrated magazine, featuring original adventures as well as differing adaptations of the original TV movie. While the comic book was closely based upon the series, and geared toward a young audience, the magazine was darker and more violent and seemed to be based more upon the literary version of the character, aimed at adult readers. Both magazines were cancelled around the same time the TV series ended. Artists Howard Chaykin and Neal Adams were frequent contributors to both publications. Steve Kahn, who had previously published magazines on the Beatles and the teen fan magazine FLiP, worked with MCA and Charlton in overseeing and publishing these books.[citation needed]

text: A British comic strip version was also produced, written by Angus P. Allan, drawn by Martin Asbury and printed in TV comic Look-In. A series of standalone comic strips was printed on the packaging of a series of model kits by Fundimensions based upon the series. In Colombia, a black and white comic book series was published in the late 70s, with art and stories by Jorge Peña. This series was licensed by Universal studios to Greco (Grupo Editorial Colombiano), then known as Editora Cinco, now part of Grupo Editorial Televisa. In France, Télé-Junior, a magazine devoted to comic book adaptations of all sorts of TV series and cartoons also featured a Six Million Dollar Man comic (under its French title, L'Homme qui valait trois milliards) with art by Pierre Le Goff and stories by P. Tabet and Bodis. A tradepaperback reprinting several episodes from the magazine was released in October, 1980.[6]

text: In 1996, a new comic book series entitled Bionix was announced, to be published by Maximum Press. The comic was to have been an updated version of both the Six Million Dollar Man and the Bionic Woman and feature new renditions of the two characters. Although the magazine was advertised in comic book trade publications, it was ultimately never published.[7]

text: On August 24, 2011, Dynamite Comics published the first issue of The Bionic Man, an adaptation written by Kevin Smith based upon a screenplay he'd written for a never-produced 1990s motion picture version of The Six Million Dollar Man. After concluding the adaptation in the spring of 2012 the comic series moved on to original stories, as well as a re-imagining of the original TV series' Secret of Bigfoot storyline. A spin-off comic re-imagining The Bionic Woman followed a few months later, and in January 2013 Dynamite launched a crossover mini-series, The Bionic Man vs. The Bionic Woman. The artwork in these series, covers and interiors, varies between Austin being rendered in the likeness of Lee Majors and not. As 2014 began, Dynamite discontinued its reboot titles and replaced them with a new ongoing series, The Six Million Dollar Man Season 6, continuing the adventures of Austin from the conclusion of the 1977-78 season and featuring not only the likeness of Lee Majors, but also other recurring actors such as Richard Anderson, as well as Darren McGavin as Oliver Spencer from the first TV movie. Jaime Sommers was reintroduced from issue 3, with a spin-off comic series, The Bionic Woman Season 4, announced in June 2014 with a scheduled launch in the fall of 2014.

text: Audiobooks[edit]

text: Peter Pan Records and its sister company Power Records published several record albums featuring original dramatized stories (including an adaptation of the pilot film), several of which were also adapted as comic books designed to be read along with the recording. Three albums' worth of stories were released, one of which featured Christmas-themed stories. Individual stories were also released in other formats, including 7 in (18 cm) singles.

text: Film[edit]

text: Universal Pictures developed a screenplay in 1995 with Kevin Smith, but the outing never materialized. In December 2001, it was announced that Universal had pacted with Dimension Films on the project after Dimension president Bob Weinstein saw its potential as a franchise.[8] Universal retained film rights to the original TV show, while Dimension purchased the rights to the Cyborg novel,[9] as well as Caidin's three other novels in the series: Operation Nuke, High Crystal and Cyborg IV. Larry Gordon and Scott Faye were going to produce with Paul Rosenberg's Collision Entertainment.[8] Smith's screenplay was later adapted for The Bionic Man, an ongoing comic book series launched in 2011 by Dynamite Comics.

text: In October 2002, Trevor Sands was hired to write a new screenplay, titled The Six Billion Dollar Man,[10] but Dimension scrapped it when actor Jim Carrey pitched a comedic take on the material for him to star in, with Scot Armstrong as writer and Todd Phillips as director/co-writer. Filming was expected to begin in 2004.[9]

text: In a July 2006 interview at Comic Con,[11] Richard Anderson (who played Oscar Goldman in the series) stated that he was involved with producing a movie of the series, but the rights were at the time in litigation between Miramax and Universal.

text: On November 6, 2014, it was announced that a feature film, tentatively titled The Six Billion Dollar Man, would go into production. Mark Wahlberg was set to play Colonel Steve Austin, and Peter Berg as director. Filming was to begin in early 2015, for a theatrical release the following year.[12][13] On November 2, 2015 it was reported that Berg had left the film and had been replaced by Damian Szifron, who will also write the film. Filming was to begin in September 2016 with a December 22, 2017 release date.[14] In December 2017, The Weinstein Company sold the film's rights to Warner Bros.[15] Warner Bros. hopes to start filming the movie in Summer 2018.[16] Warner Bros. has set an early summer 2019 release for the film.[17]

text: Cultural influence[edit]

text: In Brazil, under the military dictatorship, some important government officials – previously elected by direct suffrage – were appointed by the President, or elected indirectly, out of a shortlist picked by the President. These politicians were called "bionic" (biônicos), due to the series' popularity, and the association with the perceived extraordinary power and influence held by the appointed officials. Between 1964 and 1985, Brazil came to have "bionic" senators, governors and mayors. With the 1988 Constitution of Brazil, all "bionic" appointments were abolished.[18][19][20]

text: In Israel, the series was re-titled The Man Worth Millions since "six million" evoked memories of The Holocaust—specifically the most commonly quoted estimate of the number of Jewish victims.[21]

text: Award[edit]

text: In 2003, Lee Majors won TV Land's "Superest Superhero" award.[22]

text: Home media[edit]

text: Universal Playback released the first two seasons of The Six Million Dollar Man on DVD in Region 2 and Region 4 in 2005–2006. The first three seasons were also released on the Italian market (Region 2) in late 2008. The season 1 release also features the three pilot movies that preceded the weekly series.

text: The Region 1 (North America) release, along with that of The Bionic Woman was one of the most eagerly awaited; its release had been withheld for many years due to copyright issues regarding the original novel. In fact, with the exception of a few episodes released in the DiscoVision format in the early 1980s and a single VHS release of the two-part The Bionic Woman storyline that same decade, the series as a whole had never been released in North America in any home video format.

text: On July 21, 2010 however, Time–Life (under license from Universal) announced the release of a complete series box set of The Six Million Dollar Man on DVD in Region 1 for the first time on November 23, 2010.[23]  The 40-disc set features all 99 episodes of the series as well as the three pilot films and the three reunion TV-movies which also feature Jaime Sommers, along with several episodes of The Bionic Woman that were part of inter-series crossovers (i.e. part one aired on one series, and part two on another) in order to include complete storylines.  In addition, the set features extensive bonus features including interviews and featurettes with all major cast members and the set comes encased in collectible packaging that includes a sound chip, activated when the box is opened, that plays back part of the first season opening credits dialogue.[24] The release is available directly through Time-Life's "6mdm" website as well a through several third-party on-line vendors.

text: In November 2011, Universal Studios Home Entertainment began releasing individual season sets of the series on DVD, available in retail stores.  It has subsequently released all five seasons.[25][26][27][28]  The fifth and final season was released on February 18, 2014.[29]

text: Several episodes of The Six Million Dollar Man actually saw their North American DVD debut several weeks in advance of the box set, as Universal Home Video included the three "crossover" episodes that helped launch The Bionic Woman as bonuses on the October 19, 2010 DVD release of Season 1 of The Bionic Woman.[30]

text: On October 13, 2015, Universal Studios released a retail version of The Six Million Dollar Man- The Complete Series on DVD in Region 1.[31]

text: In Region 2, Fabulous Films acquired the rights to the series in 2012 and subsequently released seasons 3-5 on DVD on October 1, 2012.[32][33][34]  It also re-released the first two seasons on February 25, 2013.[35][36]  A 40-disc complete series boxset was released on April 2, 2012.[37]

text:
DVD Name
Ep #
Release dates

Region 1

Region 2

Region 4

The Complete Season One

16

November 29, 2011

September 26, 2005 February 23, 2013 (Re-release)

August 15, 2006

The Complete Season Two

22

October 2, 2012

October 23, 2006 February 23, 2013 (Re-release)

October 24, 2006

The Complete Season Three

22

February 19, 2013

October 1, 2012

N/A

The Complete Season Four

23

October 8, 2013

October 1, 2012

N/A

The Complete Season Five

21

February 18, 2014

October 1, 2012

N/A

The Complete Series

99

November 23, 2010 October 13, 2015 (Re-release)

April 2, 2012

TBA


document_title: List of fictional characters with stars on the Hollywood Walk of Fame

question_text: when did bugs bunny get a hollywood star

root

text: Fictional characters[edit]

text: The following fictional characters have received stars on the Hollywood Walk of Fame; 13 in motion pictures and four in television.

tag: p

text:
Character
Current copyright holder
In
Creator
Date
Location
Reason

Big Bird
Sesame Workshop

Jim Henson
(1994-04-21)April 21, 1994[1]
7021 Hollywood Blvd.
For his role on the children television show, Sesame Street.

Bugs Bunny
Warner Bros.

Tex Avery
(1985-12-10)December 10, 1985[2]
7007 Hollywood Blvd.
For his role in Looney Tunes short films.

Donald Duck
The Walt Disney Company

Walt Disney
(2004-08-09)August 9, 2004[3]
6840 Hollywood Blvd.
For his role in animated films.

Godzilla
Toho

Tomoyuki Tanaka
(2004-11-29)November 29, 2004[4]
6925 Hollywood Blvd.
For his role in films.

Kermit the Frog
The Walt Disney Company

Jim Henson
(2002-11-14)November 14, 2002[5]
6801 Hollywood Blvd.
For his leading role in The Muppet Show.

Mickey Mouse

Walt Disney
Ub Iwerks
(1978-11-13)November 13, 1978[6]
6925 Hollywood Blvd.
For his role in animated films. Dedicated on his 50th Anniversary.

Minnie Mouse

Walt Disney
Ub Iwerks
(2018-01-22)January 22, 2018[7]
6834 Hollywood Blvd.
For her role in animated films, and for her role as a prominent fashion influencer since her debut.

The Munchkins
Turner Entertainment [8]

L. Frank Baum
(2007-11-20)November 20, 2007[9]
6900 Hollywood Blvd.
For their role in The Wizard of Oz.

The Muppets
The Walt Disney Company

Jim Henson
(2012-03-20)March 20, 2012[10]
6834 Hollywood Blvd.
For their role in motion pictures.

Rugrats
Nickelodeon

Arlene Klasky
Gábor Csupó
Paul Germain
(2001-06-28)June 28, 2001[11]
6600 Hollywood Blvd.
For their 10th anniversary on their television show, Rugrats.

Shrek
Universal Studios

William Steig
(2010-05-20)May 20, 2010[12]
6931 Hollywood Blvd.
For his role in his animated feature films.

The Simpsons
20th Century Fox

Matt Groening
(2000-01-14)January 14, 2000[13]
7021 Hollywood Blvd.
For their 10th anniversary on their television show, The Simpsons.

Snoopy
Peanuts Worldwide

Charles M. Schulz
(2015-11-02)November 2, 2015[14]
7021 Hollywood Blvd.
For his role in the Peanuts animated television specials and films.

Snow White
The Walt Disney Company

The Brothers Grimm
(1987-06-28)June 28, 1987[15]
6920 Hollywood Blvd.
For her role in the first feature-length Disney animated film, Snow White and the Seven Dwarfs. Perhaps dedicated on the film's 50th anniversary.

Tinker Bell

J. M. Barrie
(2010-09-21)September 21, 2010[16]
6834 Hollywood Blvd.
For her silent role in all of the Neverland films.

Winnie the Pooh

A. A. Milne
(2006-04-11)April 11, 2006[17]
6834 Hollywood Blvd.
For his role in his animated films.

Woody Woodpecker
Universal Studios

Walter Lantz
(1990-09-13)September 13, 1990[18]
7000 Hollywood Blvd.
For his role in his animated films.

tag: table

text: Live-action animals[edit]

text: Three live-action canines have stars on the Walk.

text:
Character
Parent Company
In
Date
Location

Lassie
MGM

(1960-02-08)February 8, 1960[19]
6368 Hollywood

Rin Tin Tin
Warner Bros.
Mascot Pictures

(1960-02-08)February 8, 1960[20]
1623 Vine

Strongheart
Associated First National Pictures

(1960-02-11)February 11, 1960[21]
1724 Vine

text: Corporate entities[edit]

text: Several corporate entities are on the Walk. All are nominated in the "Special Recognition Category", and as with Tom Bradley and Johnny Grant, many have special logos other than the five normal categories.

text:
Company
Product
Logo
Date
Location
Reason

Disneyland
Theme park
Sleeping Beauty Castle
14 July 2005
6834 Hollywood
For the park's 50th anniversary.


document_title: Atom

question_text: when was the idea of the atom first introduced

question_tokens: when was the idea of the atom first introduced

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 ancient Greek philosophers. 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.[1]

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.[2] 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.[3][4][5] French physicist Jean Perrin used Einstein's work to experimentally determine the mass and dimensions of atoms, thereby conclusively verifying Dalton's atomic theory.[6]

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.[7] 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.[8] 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.[9] 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.[10]

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.[11] 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.[12]

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.[13] 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.[14]

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.[15]

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.[16] As the chemical properties of the elements were known to largely repeat themselves according to the periodic law,[17] 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.[18]

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.[19]

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.[20] 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.[21][22]

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.[23] 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.[24]

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.[25][26] A year later, Lise Meitner and her nephew Otto Frisch verified that Hahn's result were the first experimental nuclear fission.[27][28] In 1944, Hahn received the Nobel prize in chemistry. Despite Hahn's efforts, the contributions of Meitner and Frisch were not recognized.[29]

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.[30] 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.[31]

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.[32] 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,[33] 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.[34] 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.[35][36]

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.[35][36]

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.[37] 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.[38]

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.[39]

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.[40]

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.[40] 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.[41] 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.[42][43]

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.[44]

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.[45] 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.[40]

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.[46] 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.[47] Orbitals can have one or more ring or node structures, and differ from each other in size, shape and orientation.[48]

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.[47]

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,[49] compared to 2.23 million eV for splitting a deuterium nucleus.[50] 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.[51]

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,[52] 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.[53] 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.[54][55]

text: About 339 nuclides occur naturally on Earth,[56] 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).[57][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.[58][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.[58][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.[59] Hydrogen-1 (the lightest isotope of hydrogen which is also the nuclide with the lowest mass) has an atomic weight of 1.007825 u.[60] 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).[61] The heaviest stable atom is lead-208,[54] with a mass of 7002207976652100000♠207.9766521 u.[62]

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.[59]

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.[63] 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.[64] 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).[65] Consequently, the smallest atom is helium with a radius of 32 pm, while one of the largest is caesium at 225 pm.[66]

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.[67][68] Significant ellipsoidal deformations have been shown to occur for sulfur ions[69] and chalcogen ions[70] 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.[71] A single drop of water contains about 2 sextillion (7021200000000000000♠2×1021) atoms of oxygen, and twice the number of hydrogen atoms.[72] 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.[73]

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.[74]

text: The most common forms of radioactive decay are:[75][76]

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.

tag: ul

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.[74]

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.[77]

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.[78]

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.[78][79]

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.[80][81]

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.[82] 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.[83] 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.[84]

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.[85]

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.[86] 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.[87] 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.[88]

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.[89]

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.[90] 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.[91] 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.[92]

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.[93][94]

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.[95] 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.[96] 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.[97][98] This super-cooled collection of atoms then behaves as a single super atom, which may allow fundamental checks of quantum mechanical behavior.[99]

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.[100][101]

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.[102]

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.[103]

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.[104] Helium was discovered in this way in the spectrum of the Sun 23 years before it was found on Earth.[105]

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.[106] 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.[107] 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.[108] 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.[109] (The remainder of the mass is an unknown dark matter.)[110]

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.[111][112][113]

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.[114]

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;[115] 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.[116] 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.[117] Elements such as lead formed largely through the radioactive decay of heavier elements.[118]

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.[119][120] 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.[121]

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.[122] Some atoms on Earth have been artificially generated either deliberately or as by-products of nuclear reactors or explosions.[123][124] Of the transuranic elements—those with atomic numbers greater than 92—only plutonium and neptunium occur naturally on Earth.[125][126] Transuranic elements have radioactive lifetimes shorter than the current age of the Earth[127] and thus identifiable quantities of these elements have long since decayed, with the exception of traces of plutonium-244 possibly deposited by cosmic dust.[128] Natural deposits of plutonium and neptunium are produced by neutron capture in uranium ore.[129]

text: The Earth contains approximately 7050133000000000000♠1.33×1050 atoms.[130] 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.[131][132] This atomic matter forms networked arrangements that lack the particular type of small-scale interrupted order associated with molecular matter.[133]

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.[134] The most likely candidate for a stable superheavy atom, unbihexium, has 126 protons and 184 neutrons.[135]

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.[136][137] However, in 1996 the antimatter counterpart of the hydrogen atom (antihydrogen) was synthesized at the CERN laboratory in Geneva.[138][139]

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.[140][141][142]