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460
Democritus
400 BC
Democritus discovered that everything is made of atoms, atoms are indivisible, between atoms lies empty space, atoms are indestructible, they are always moving, there are an infinite number of atoms, and atoms come in different shapes and sizes
Indivisible, solid sphere model -
460
Indivisible, solid sphere model
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Antoine Levoisier
mid 1700s
He used this experiment to help himself come up with the Law of Conservation. The law states that matter cannot be made or destroyed. He also hints at the rearrangement of matter in reactions. Matter rearranged, but never disappeared.
Indivisible, solid sphere model -
Joseph Proust
1794
The law states that the ratio of elements in a compound is always the same/constant. He also hinted at the 'lego'ness of matter; he believed that matter could be put together in certain patterns to make bigger, different, unique matterIndivisible, solid sphere model -
John Dalton
1803
Dalton's ideas were that the atoms of an element were the same as its weight, the atoms of different elements had different weights; and atoms combined only in small whole-number ratios to form compounds
Indivisible, solid sphere model -
Michael Faraday
September 22, 1791
This he found meant that there was something in the center of the atoms, called the nucleus. This led to his nuclear model of an atom. It was the first of its kind to display the nucleus that he found while experimenting.
cell with nucleus -
Henri Becquerel
1896
While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays.
Plum Pudding Model -
J.J. Thomson
1897
Thomson carried out an investigation to find that positive rays/cathode rays were streams of negatively charged particles with a mass about 1,000 times smaller than a hydrogen atom. This resulted to the discovery of the electron and the positively charged ion.
Plum Pudding Model -
Plum Pudding Model
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Max Planck
Founder of the quantum theory and also did extensive research on the heat theory. That all particles that have energy heat up.
Contribution to our understanding of atoms: This produced the kinetic theory and also showed that all tiny particles warm up and move around more.
Plum Pudding Model -
Marie & Pierre Curie
1898
Studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium. -
Robert Milikan
1909
Milikan confirmed that electrons were a negative charge by suspending tiny oil droplets into an electric field.Oil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron -
Ernest Rutherford
1911
He found that there is a positive charge inside the nucleus of the atom. He confirmed Nagaoka’s model which Nagaoka and the rest of the world thought was incorrect at the start.
Contribution to our understanding of atoms: This helped find that the positive charge is confined inside the nucleus only and are called protons. Another part of the atom was discovered later.
cell with nucleus -
Lisa Meitner
1938
Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction. -
Otto Hahn
March 8, 1879
Also known as “the father of nuclear chemistry”, Hahn crusaded against the use of nuclear weapons after World War II. As an influential citizen of the Federal Republic of Germany, he had also strongly opposed Jewish persecution by the Nazis. -
Albert Einstein
1905
Published the famous equation E=mc 2 -
Niels Bohr
1924
His idea was that the nucleus is made up of neutrons and protons, with the electrons revolving around the nucleus. He found that each electron shell could only hold a certain number of electrons and after that orbit is full, the next level would have to be used.
Planetary Model -
Planetary Model
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Erwin Schrodinger
August 12, 1887
took the Bohr atom model one step further. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position.
Planetary Model -
James Chadwick
1932
Chadwick discovered neutrons.They differed from alpha rays because they repelled considerable electrical forces that are in the nucleus of many heavy atoms. A neutron can then penetrate and split the nuclei of most elements.Chadwick discovered that atoms also contain neutral particles (no charge) in the nucleus. -
Louis DeBroglie
1923
Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein. -
Electron Cloud Model
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Glen T. Seaborg
1941-51
Synthesized 6 transuranium elements and suggested a change in the layout of the periodic table.
Quantum Mechanical Model -
Quantum Mechanical Model
today! -
Aristotle
400 BC
Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter.
