Atomic Structure Timeline

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Atomic Structure Timeline

465 B.C.E-Democritus:- Democritus was the student of Leucippus, who the atomic theory originated from, Democritus simply added on to it.- Democritus believed that the atom was best represented by a sinle solid sphere.- When naming the particle, Democritus chose the Greek word for invisible, 'atomos'- Democritus' theory was rejected and ignored for nearly 2,000 years.-Democritus theorized that atoms were indestructable.-Democirtus also theorized that atoms always remain in motion.

The Development of the Atomic Structure

1894-G.J. Stoney:- The term electron come from his work- Calculated the magnitude of electrons through electrolysis of water and the kenetic theory of gases.- Worked as a physicist and an astronomer assistant-

1904-J.J. Thompson:-Thompson discovered the electron.- Thompson's discovery was the restult of the study of the nature of electrict discharge.- Thompson calculated that electrons had a very large charge-to-mass ratio value.- Thompson suggested that an atom was best represented with a sphere with electrons and protons inside.- He studied the measurement of the scattering of light, X, beta and gamma rays to estimate the number of electrons in an atom.- Thompson was not the only scientist at the time that was conducting experiments on the nature of electric discharge.

1803-John Dalton:- Like Democritus, Dalton thought a solid sphere. respresented an atom- Dalton's research of gases helped him develop his theory.- Through his reaserch of gases, Dalton found that only specific proportions of gases can be combined- Dalton's law of multiple proporrtions and findings through experimentation with gases became the basis for his atomic laws.- Like Democritus, Dalton theorized that atoms were indestructable.- Dalton's theory helped explain chemical phenomena that had gone unxplained prior to his discoveries.- His theory includes five postulates:1.) Everything is made out oof invisible and indestructable atoms2.) All atoms of a certain element are identical3.) Different elements consist of atoms with different physical and chemical properties.4.) Compounds are formed by whole number ratios of atoms or elements (Law of Definie Proportions)5.) A chemical reaction takes place when atoms rearrange, combine, or separate. (Law of Conservation of Mass)- Dalton's second postulate was later proven to be wrong due to the discovery of different isotopes of the same element.

1704-Sir Isaac Newton:- Studied gases- His work was impeded by the church- Also studied the possibility of atoms existing- proposed a mechanical universe where small solid matter is constantly in motion- Began to understand that atoms are not stationary

1913-Niels Bohr:- Bohr's model became the basis for the quantum theory- Discovered that electrons travel in separate orbits- Modified Rutherford'd model to require that electrons be place in orbits of specific energy and size- Found that Ruherford''s model had an issue with stability- His discoveries helped with the first attempts to split uranium atoms

1896-Henri Becquerel:- Discovered radioactivity- Discovered radioactive beta particles- Becquerel was not originally looking ofr radioactivity- he had simply discovered it by chance through his experiments for something else.-Suffered from recurring bruns due to handling radioactive stones.- The basic unit of radioactivity, or Becquerel, was named after him.

1898-Marie Sklodowska Curie:- her research led to the isolation of polonium.- Developed mathod of separating radium from radioactive subastances.- Promoted radium as a remedy to alleviate pain- Was a big promoter of science and pushed for a radioactivity laboratory to be built in her native city.- With her husband, she was awarded that Nobel Prize in 1903

1913-Henry Moseley:- Mosely was a chemist- Moseley studied under Rutherford- Discovered that the ordering of atomic numbers coinsided with the wavelength of the X-ray emissions - Worked with X-ray to measure the wavelength of spectral lines- To find this he shot electrons a a metal plate which causes that atoms of it to emit X-rays. - Rearranged Mandeleev's periodic table to be organized by atomic number rather than atomic weight- Worked with C.G. Darwin to solve complicated math problems

1904-Richard Abegg:- Discovered that the noble gases were stable due to there being eight electrons on the outermost shell of the electron cloud- Through this discovery he proposed the vallence bond theory- His rule states that the difference between the maximum positive and negative valence of an element is usually eight.- Founds that some elements are less likely to bond into molecules- From this discovery he concluded that more stable elements had full electron shells

1923-De Broglie:- Worked heavily with X-rays and contemplated the ual nature of light- Claimed that matter might behave i a similar manner- His theory oof electron waves caught the aattention of Albert Einstein- His theory improve our knowledge on the physical nature of the atomic scale- Discovered that electrons can act like waves

1926-Erwin Schrodinger:- Used mathematical equations to show the probability of an electron being in a certain position- Schrodinger used his equations to come up with a model of the elctron cloud- His model consists of a dense nucleus and an electron cloud with different orbitals.- Worked with Werner Heisenburg- His cat experiment helps prove the point that sometimes there is more than one correct answer to a problem

1942-Enrico Fermi:- KNwon for his achievements in theoretical and experimental physics- Evolved the Beta-decay theory- Remembered for his work on the first nuclear reactor and for his contributions to the quantum theory- His work was ccarried forward to New Mexico where the first atomic bomb was set off

1906-Hans Geiger:- Invented the Geiger counter that measures radiation- Used his invention to confirm the Compton effect- Briefly participated in Germany's attempt to develop an atomic bomb- In 1929 he made his first obsservation of the cosmic-ray shower- Investigated cosmic-rays, artificial radioactivity, and nuclear fission.

1909-Robert Millikan:- Millikan Determined the unit charge for electrons- His oil drop experiment aided him in his discovery- He worked on the oil drop experiment with one of his graduate students Harvey Fletcher.- To measure the unit charge of electrons he suspended a drop of oil between two capacitor plates-, Millikan was awrded the Nobel Prize for Physics in 1923.

1869-Dmitri Mendeleev:- Discovered the periodic table- Proposed that some of the elements that had behaviors that did not agree with his predictions had been measured incorrectly for their atomic mass.- predicted the existance of eight new elements- Aknowledged the importance of atommic weight- Created a 500 page text book about chemistry in just 61 days

1930-Paul Dirac:- Laid the groundwork for quantum mechanics and electrodynamics- Came up with the quantum ield theory after reworking his own equation- Predicted the existance of antimatter and amtter-antimatter annihilation-Discovered magnetic monopole solutions

1911-Ernest Rutherford:- Rutherford suggested that electrons orbited the nucleus of an atom.- Postulated that the nucleus of an atom was small and dense- Based his discoveries on his gold foil experiment- In his experiment , Rutherford used a radioactive substance that was capable of projecting alpha particles and observed weather or not the particles where able to pass through the gold foil or if they were deflected by the gold foil.- Rutherford was actually a physicist and made his discoveries wholly through physics

1941-51-Glenn Seaborg:- Invovled in the discovery of nine transuranium elements- His discoveries suggested a change in the layout of the periodic table- The changes he proposed are knwon as the actinide concept- The changes he wanted to make to the periodic table were the most signifigant sincce Mandeleev's conceptiion- In 1951 he was aawarded the Nobel Prize for chemistry

1938-Meitne, Hahn & Strassman;- Discovered that when uranium is bombarded with neuttrons, it splits- Produced Barium- Found that Barium was a stable isotope that was a product of radioactive decay- The discovery of the splitting f the atom was brought to the United States by Bohr- The discovery of the splitting of the atom resulted in the Manhattan Project


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