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460
Democritus
Born around 460 B.C., Democritus was an acient Greek philosopher who is credited with the formation of the atomic theory. He believed that everything was made of atoms which are indestructable. He also believed that the shape and charcteristics of atoms corresponded with the element. For example, irona toms are strong and hard. -
Antoine Lavoisier
Born in Paris, France in 1743, he is considered to be the father of modern chemistry. Lavoisier named and recognized oxygen in 1778 and hydrogen in 1783 and discovered the role oxygen has in combustion. He also wrote up a larger list of elements. -
John Dalton
Born in Eaglesfield, England in 1766, John Dalton founded the atomic theory of matter. He propsed that the atom was similar to a billiard ball. Dalton also believed that differetn elements have different weights, with hydrogen having a weight of 1. -
Dalton's Atomic Theory
Dalton's Atomic Theory states:
1. Elements are made of extremely small particles called atoms.
2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
3. Atoms cannot be subdivided, created, or destroyed.
4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds
5. In chemical reactions, atoms are combined, separated, or rearranged. -
Dmitri Mendeleev
Dmitri Mendeleev was born in Russia and he pioneered the periodic law and formed his own version of the periodic table of elements. He used his own table to correct properties of some elements and to predict others that were undiscovered. -
J.J. Thomson
Born in Manchester, England, Thomson discovered the first subatomic particle; the electron. He was able to display negative charges in cathode rays exist. He won a noble prize in 1906 for this discvoery. -
Robert Millikan
Born in Morrison, Illinois, Millikan won a nobel prize in physics for his discover of the electric charge of the electron. Millikan used his oil drop experiment to prove his theory that the electron is negatuvely charged -
Ernest Rutherford
Born in Brightwater, New Zealand, Rutherford is known as the father of nuclear physics. During his studies at McGill University, he used the gold foil experiment to prove that there was a mass at the center of the atom, the nucleus. He also discovered the proton while creating a nuclear reaction between nitrogen and alpha particles. -
Niels Bohr
Born in Copenhagen, Denmark, Bohr made huge contributions to the structure of an atom and quantum theory. He developed a model of the atom known as the Bohr Model that showed a nucleus at the ceneter of the atom with electrons orbiting it. -
Erwin Schrodinger
Born in Austria, Schrodinger helped develop the quantum theory. He helped form a basis of wave mechanics. He propsed a different idea of wave functions and was criticized for this. -
Henry Moseley
Born in the United Kingdom, Moseley is responsible for the justification of the atomic number of elements. He proved that the nucleus contains positive charges that are equal to the atoms atomic number on the periodic table. -
James Chadwick
In 1932, English physicist James Chadwick discovered the neutron. During his experiements at the University of Cambridge, he used gamma ray radiation theories to prove that there were uncharged particles in atoms that were named neutrons. -
Cathode Ray Tube
German physicist Ferdinand Braun invented the cathode ray tube in 1897 but it was JJ Thomson that made it famous by deflecting cathode rays. The tube acclerates electrons onto a screen to create images. -
Plum Pudding Atomic Model
Proposed by JJ Thomson who also discovered the existence of the electron. This model does not take into account the nucleus but instead proposes that the negative subatomic particles float around in a positively charged cloud. The cloud represent pudding. -
Gold Foil Experiment
Conducted by Hans Geiger and Ernest Marsden, the gold foil experiment was performed to prove the structure of an atom. The experiment revealed that there was an extremely dense section of the atom that we know as the nucleus. -
Quantum Mechanical Model
This model uses mathematics and is based on quantum theory. Quantum theory states that matter has properties associated with waves. This model uses complex shapes and is more difficult to understand than the Bohr Model. -
Rutherford Model
Ernest Rutherford developed his model of the atom in 1911 and disproved the Plum Pudding Model. Rutherford's model took into account a very dense region at the center of the atom that is now called the nucleus. He conducted the gold foil experiment to prove his theory of a nucleus. -
Bohr Planetary Model
Created by Neils Bohr in 1913, this model of the atom depicts a positively charged nucleus with electrons that orbit around it. The Bohr model of the atom is primitive but displays quantum mechanics and energy levels. -
Electron Cloud
Developed by Erwin Schrodinger and Werner Heisenberg, the electron cloud desribes where electrons are as they rotate around the mucleus of the atom. The electron cloud model says that electrons do not orbit the nucleus and that we cannot know where they are.
