Atomic Theory Project

Kai VegaRachel Martinez

12-2-10Chemistry 5th

James

Chadwick:In 1932, Chadwick made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons. In 1935, he received the Nobel Prize for Physics. Chadwick was knighted in 1945, and died in 1974 at Cambridge

Eugen Goldstein

In 1886 Goldstein showed that cathode

rays can cast shadows, then demonstrated how such rays are emitted, perpendicular to the cathode surface, and can be manipulated with

magnetic fields. Goldstein's work suggested the presence of the proton -- a positively

charged particle, later discovered by Ernest Rutherford. He was Jewish.

DemocritusDemocritus along with his partner Leucippus, was the first to say that everything was made up of atoms, which are physically, but not geometrically, indivisible; that between atoms lies empty space; that atoms are indestructible; have always been, and always will be, in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. Of the mass of

atoms, Democritus said "The more any indivisible exceeds, the heavier it is." But their exact position on weight of atoms is disputed.[1]

Robert Millikan His earliest major success was the accurate determination of the charge carried by an electron, using the "falling-drop method"; he also proved that this quantity was a constant for all electrons (1910), thus demonstrating the atomic structure of electricity. He has been the recipient of the Comstock Prize of the National Academy of Sciences, of the Edison Medal of the American Institute of Electrical Engineers, of the Hughes Medal of the Royal Society of Great Britain, and of the Nobel Prize for Physics 1923. He was also made

Commander of the Legion of Honour, and received the Chinese Order of Jade.

Simplified scheme of Millikan’s oil-drop experiment.

The scheme of the experiment is as follows: An atomizer sprayed a fine mist of oil droplets into the upper chamber. Some of these tiny droplets fell through a hole in the upper floor into the lower chamber of the apparatus. Millikan first let them fall until they reached terminal velocity due to air resistance. Using the microscope, he measured their terminal velocity, and by use of a formula, calculated the mass of each oil drop.

Next, Millikan applied a charge to the falling drops by irradiating the bottom chamber with x-rays. This caused the air to become ionized, which basically means that the air particles lost electrons. A part of the oil droplets captured one or more of those extra electrons and became negatively charged.

By attaching a battery to the plates of the lower chamber he created an electric field between the plates that would act on the charged oil drops; he adjusted the voltage till the electric field force would just balance the force of gravity on a drop, and the drop would hang suspended in mid-air. Some drops have captured more electrons than others, so they will require a

higher electrical field to stop.

Particles that did not capture any of that extra electrons were not affected by the electrical field and fell to the bottom plate due to gravity

When a drop is suspended, its weight  m · g  is exactly equal to the electric force applied, the product of the electric field and the charge q · E.

The values of E (the applied electric field), m (the mass of a drop which was already calculated by Millikan), and g (the acceleration due to gravity), are all known values. So it is very easy to obtain the value of q, the charge on the drop, by using the simple formula:

m · g = q · E

Millikan repeated the experiment numerous times, each time varying the strength of the x-rays ionizing the air, so that differing numbers of electrons would jump onto the oil molecules each time. He obtained various values for q.

The charge q on a drop was always a multiple of 1.59 x 10-19 Coulombs. This is less than 1% lower than the value accepted today: 1.602 x 10-19 C.

J.J. Thomson He discovered a method for separating different kinds of atoms and molecules by the use of positive rays, an idea developed by Aston, Dempster and others towards the discovery of many isotopes. Beginning in 1895, J. J. Thomson theorized that cathode rays produced in Crookes' tubes must be composed of what he called "corpuscles", a single type of negatively charged particle. In 1897, applying his own vacuum technique to the study of these then-mysterious rays, Thomson made a

convincing argument for composition based on sub-atomic particles, "this matter being the substance from which all the chemical elements are built up". To make sense of this theory he proposed a "plum pudding model" of the atom, which was debated for several years and disproved by his former student, Ernest Rutherford. Thomson also showed a stream of channel rays could be separated into two or more parts through exposure to electrical and magnetic fields

John Dalton He proposed the Atomic Theory in 1803 which stated that (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). Dalton's theory was presented in New System of Chemical Philosophy (1808-1827). This work identified chemical elements as a specific type of atom, therefore rejecting Newton's theory of chemical affinities. Instead, Dalton inferred proportions of elements in compounds by taking ratios of the weights of reactants, setting the atomic weight of hydrogen to be identically one. Following Richter, he proposed that chemical elements combine in integral ratios. Despite the importance of the work as the first view of atoms as physically real entities and introduction of a system of chemical symbols, New System of Chemical Philosophy devoted almost as much space to the caloric theory as to atomism.

Dmitri Mendeleev 1866 he succeeded to the Chair in the University. Mendeleev is best known for his work on the periodic table; arranging the 63 known elements into a Periodic Table based on atomic mass, which he published in Principles of Chemistry in 1869. His first Periodic Table was compiled on the basis of arranging the elements in ascending order of atomic weight and grouping them by similarity of properties.  He predicted the existence and properties of new elements and pointed out accepted atomic weights that were in error. This organization surpassed attempts at classification by Beguyer de Chancourtois and Newlands and was

published a year before the work of Lothar Meyer.

Richard Abegg

Abegg introduced the concept of the electro-affinity into chemistry and made the basis for the handbook of the inorganic chemistry (1905–1939). In 1904, Abegg formulated the valence rule, after which the highest positive and highest negative electro-valence of an element yields 8 altogether. This is called Abegg's rule. The Prussian secretary of state Wilhelm Abegg was his brother.

Ernest Rutherford

His work constituted a notable landmark in the history of atomic research as he developed Bacquerel's discovery of Radioactivity into an exact and documented proof that the atoms of the heavier elements, which had been thought to be immutable, actually disintegrate (decay) into various forms of radiation.Rutherford was the first to establish the theory of the nuclear atom and to carry out a

transmutation reaction (1919) Uranium emanations were shown to consist of three types of rays, alpha (helium nuclei) of low penetrating power, beta (electrons), and gamma, of exceedingly short wavelength and great energy.Ernest Rutherford also discovered the half-life of radioactive elements and applied this to studies of age determination of rocks by measuring the decay period of radium to lead-206.

Erwin Schrodinger Erwin Schrodinger added the final piece to the puzzle of electron arrangement around the nuclei of atoms. He suggested that electrons behave in a wave-like manner rather than just as particles and that their exact location within an orbit could not be precisely calculated. His great discovery, Schrödinger's wave equation, was made at the end of this epoch-during the first half of 1926. Schrodinger began to think about explaining the movement of an electron in an atom as a wave. By 1926 he published his work, providing a theoretical basis for the atomic model that Niels Bohr had proposed based on laboratory evidence. The equation at the heart of his publication became known as Schrödinger's wave equation. This was the second theoretical explanation of electrons in an atom, following Werner Heisenberg's matrix mechanics. Many scientists preferred Schrödinger's theory since it could be visualized, while Heisenberg's was strictly mathematical. A split threatened among physicists, but Schrödinger soon showed that the two theories were identical, only expressed differently.

Niels Bohr

After receiving his doctorate in 1911, Bohr traveled to England on a

study grant and worked under J.J. Thomson, who had discovered the electron 15 years earlier. Bohr began to work on the problem of the atom's structure. Ernest Rutherford had recently suggested the atom had a miniature, dense nucleus surrounded by a cloud of nearly weightless electrons. There were a few problems with the model, however. For example, according to classical physics, the electrons orbiting the nucleus should lose energy until they spiral down into the center, collapsing the atom. Bohr proposed adding to the model the new idea of quanta put forth by Max Planck in 1901. That way, electrons existed at set levels of energy, that is, at fixed distances from the nucleus. If the atom absorbed energy, the electron jumped to a level further from the nucleus; if it radiated energy, it fell to a level closer to the nucleus. His model was a huge leap forward in making theory fit the experimental evidence that other physicists had found over the years. A few inaccuracies remained to be ironed out by others over the next few years, but his essential idea was proved correct. He received the Nobel Prize for this work in 1922

Louis de Broglie French quantum physicist Louis de Broglie introduced his theory of particle-wave duality in 1924. In his time, the wave and particle interpretations of light and matter were seen as being at odds with one another, but de Broglie suggested that these seemingly different characteristics were instead the same behavior observed from different perspectives — that particles can behave like waves, and waves (radiation) can behave like particles. It was originally written as his doctoral thesis, but his advisors at the Sorbonne concluded that they could not fully assess its merit, and suggested that he send Albert Einstein a

copy for evaluation. Einstein wrote back almost immediately, and stated that de Broglie had unraveled one of the secrets of the universe. His theory helped explain how atoms, molecules, and protons behave, inspired Erwin Schrödinger in the formulation of wave mechanics, and earned de Broglie the Nobel Prize for Physics in 1929

Friedrich

Hund

Friedrich hund Studied under Max Born. He discovered the principle of quantum tunneling (quantum mechanical barrier penetration), in a paper published in 1927. He also did significant work on the structures of atoms and molecules, molecular orbital theory known as the Hund-Mulliken theory (working with Robert S. Mulliken, the 1966 Nobel laureate in chemistry.)

Lastly, Hund's rule states that even though each orbital can hold two electrons, the electrons will occupy the orbitals such that there are a maximum number of orbitals with only one electron. Developed by the German scientist, Friedrich Hund (1896–1997), Hund's rule allows scientists to predict the order in which electrons fill an atom's suborbital shells.

Hund's rule is based on the Aufbau principle that electrons are added to the lowest available energy level (shell) of an atom. Around each atomic nucleus, electrons occupy energy levels termed shells. Each shell has a spherical s orbital and, starting with the second shell, orbitals (p, d, f, etc.) and suborbitals (e.g., 2px,2py, 2pz) with differing size, shapes and orientation (i.e., direction in space).

Wolfgang Pauli

Wolfgang Pauli was a German physicist who, in 1925, proposed the Pauli exclusion principle, which states that no two fermions may possess the same energy (occupy the same quantum state) in a given atom. He made fundamental contributions to quantum mechanics. His ability to make experiments self destruct simply by being in the same room was legendary, and has been dubbed the "Pauli effect"

He drank heavily, his first marriage lasted less than a year before ending in divorce, and his mother killed herself in 1927.

Robert Bunsen

With Gustav Robert Kirchhoff, he observed in 1859 that each element emits light of a characteristic wavelength, opening the field of spectrochemical analysis. They discovered several new elements (including helium, cesium, and rubidium) by spectroscopy. His only book

discussed methods of measuring volumes of gases. He invented the carbon-zinc battery, grease-spot photometer , filter pump, ice calorimeter, and vapor calorimeter. Though often credited with inventing the Bunsen burner, he made only a minor contribution to its development.

George Stoney Known for coining the term electron as the fundamental unit of quantity of electricity. Stoney published seventy-five scientific papers in a variety of journals, making a large impact on cosmic physics and the theory of gases. He estimated the number of molecules in a cubic millimeter of gas,

at room temperature and pressure from data obtained from the kinetic theory of gasses and after introducing the concept of an electron he set the way for J.J. Thomson to discover particles in 1897.

Marie Curie She is credited for being a pioneer in experimenting with radioactivity and for discovering polonium; also known as the “mother of Modern Physics”. She was intrigued by Henri Becquerel’s work with radioactivity in uranium so she tested radioactivity in other elements and concluded that radioactivity is not a property of an interaction between elements, but rather an atomic property. She named polonium after her homeland: Poland.

Frederick Soddy

Best known for explaining (along with Rutherford) that radioactivity is caused by trasmutated elements--thereby involving nuclear reactions. He is also credited for proving the existence of isotopes in certain radioactive elements.

In 1900, Soddy and Rutherford realized that the anomalous behavior of radioactive elements was because they decayed into other elements; said decay also produced alpha, beta, and gamma radiation--something

that the two men worked on to prove that transmutation was to blame.By putting a sample of radiumin a thin-walled glass envelope inside an evacuated glass bulb, Soddy verified that the decay of radium produced alpha particles composed of positively charged nuclei of helium. After leaving the experiment running for a long period of time a spectral analysis

of the contents of the former evacuated space revealed the presence of helium

Max Planck

Planck was the founder of quantum theory. In the early 1900’s he made the base for quantum theory, which many other scientists improved upon later on.

Werner Heisenberg.

Heisenberg, along with Max Born and Pascual Jordan, set forth the matrix formulation of quantum mechanics in 1925. Heisenberg developed his Uncertainty Principle, while working on the mathematical foundations of quantum mechanics. In his paper on the Uncertainty Principle, Heisenberg used the word "Ungenauigkeit" (meaning "imprecision").Heisenberg was president of the German Research Council, chairman of the Commission for Atomic Physics, chairman of the Nuclear Physics Working Group, and president of the Alexander von Humboldt Foundation.

Henry Moseley

In 1913 Moseley developed the application of X-Ray Spectra; determined the number of positive-charged particles in a nucleus. Moseley experimented with Bohr’s theory, later thereby proving it to be true. Moseley also improved Mendeleev's periodic table.

Citations

"James Chadwick - Biography." Nobelprize.org. Web. 01 Dec. 2010.

<http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html>.

"Eugen Goldstein." NNDB: Tracking the Entire World. Web. 01 Dec. 2010.

<http://www.nndb.com/people/887/000169380/>.

"Eugen Goldstein." Purdue University College of Science Welcome. Web. 01 Dec. 2010.

<http://chemed.chem.purdue.edu/genchem/history/goldstein.html>.

"Robert Millikan: The Oil-Drop Experiment - Determining The Charge of the Electron." The Orchid

Grower: A Juvenile Science Adventure Novel. Web. 01 Dec. 2010.

<http://www.juliantrubin.com/bigten/millikanoildrop.html>.

"Dalton, John (1766-1844) -- from Eric Weisstein's World of Scientific Biography." ScienceWorld.

Web. 01 Dec. 2010. <http://scienceworld.wolfram.com/biography/Dalton.html>.

"Dmitri Mendeleev ~ History of the Periodic Table." Chemistry and New Zealand. Web. 01 Dec. 2010.

<http://www.chemistry.co.nz/mendeleev.htm>.

"Robert Wilhelm Bunsen." Corrosion Science and Engineering Information Hub. Web. 01 Dec. 2010.

<http://www.corrosion-doctors.org/Biographies/BunsenBio.htm>.

"Atomic Theory." Docstoc – Documents, Templates, Forms, Ebooks, Papers & Presentations. Web. 01

Dec. 2010. <http://www.docstoc.com/docs/23880101/atomic-theory>.

All done now!

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