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400 BCE
Democritus
Democritus did some really hard thinking and came up with the idea that everything was made up of smaller "building blocks." He named these blocks "atomos" or atoms. -
John Dalton
Dalton discovered many things about atoms. Dalton's atomic theory included:
1.) All matter is made up of atoms
2.) Atoms of the same element are identical
3.) Compounds form when two or more different elements bond chemically
4.) Atoms are not destroyed during chemical reactions -
Indivisible, Solid Sphere Model
This model, also known as the Billiard Ball Model, was created by Dalton. -
Sir William Crookes
Crookes discovered a new element and named it Thallium. He also studied and improved the cathode ray tube which became vital in the advancement of the atomic theory. -
J.J. Thomson
Thomson discovered the electron using the cathode ray tube experiment. He took a cathode ray tube and put a magnet next to it. The light beam inside curved toward the positive end, and away from the negative end. This meant that atoms had negatively charged parts. -
Plum Pudding Model
Thomson's plum pudding model showed that atoms are spheres with an overall positive charge (pudding) and randomly appearing negative electrons (plums). -
Albert Einstein
Einstein used complicated mathematical equations to prove the existence of atoms. -
Johannes Wilhelm Geiger
Geiger introduced the first successful detector which counted individual alpha particles, which will later be used in the gold foil experiment, and ionizing radiation. The first "Geiger counter" measured radioactivity. -
Robert Millikan
Millikan measured the charge of the electron. He did so by the oil drop experiment. He suspended a droplet of oil between a positively and a negatively charged plate. Then, he measured the charge of the oil drop. -
Ernest Rutherford
Rutherford discovered that atoms have nuclei. He also discovered that the negatively charged electrons float around the positively charged nucleus. He discovered this by shooting positively charged alpha particles at pure gold foil. As expected, some particles passed through the foil, but surprisingly, some particles bounced off! -
Rutherford's Nuclear Model
Earnest Rutherford expanded upon Thomson's pudding model by depicting that the negative electrons float in the atom's empty space, circling the positive nucleus. -
Niels Bohr
Bohr discovered that electron orbitals are quantized, which means they circle within bounds. It was previously believed that gravity held electrons to the nucleus, but Bohr reasoned that it was electrical charge holding them within bounds. -
Planetary (Solar System) Model
This model was created by Bohr. He said that electrons orbited around the nucleus, much like planets to the sun, instead of just circling around aimlessly. -
Henry Gwyn Jeffreys Moseley
Moseley discovered the atomic number. This number identified elements according to their number of protons. -
Erwin Schrödinger
Schrödinger, using mathematical equations, described the likelihood of finding on electron in a certain position. He showed this in his quantic mechanical model. -
Louis de Broglie
De Broglie discovered the wave nature natures of electrons. This wave nature restricted the motion of the electron. -
James Chadwick
Chadwick discovered the neutron in the nucleus. He bombarded Beryllium atoms with alpha particle rays and an unknown radiation was produced. -
Electron Cloud Model
This model, created by Schrödinger, assigns electrons to certain orbitals around the nucleus. This orbital ordering can also displayed in the columns of the periodic table.
