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440 BCE
Democritus
He discovered the universe was made of tiny atoms that formed larger units. Atoms make up matter and are separated by empty space for them to move. Atoms are solid and unchangeable. Atoms differ is size and shape. -
John Dalton
He continued Democritus’ ideas by creating his own modern atomic theory. He discovered atoms are indivisible and indestructible with different weights and chemical properties. Atoms can’t be created or destroyed and combine together to form compounds. Elements are made of atoms. -
Dmitri Mendeleev
He discovered the periodic table was configured by the element’s atomic weight. -
Eugene Goldstein
He discovered that electrons travel from the negative cathode to the positive and an additional ray travels in the opposite direction. So this concluded that they carry the opposite charge. They were known as cathode rays. -
JJ Thomson
He discovered the electron in 1897 and proved atoms can be divided. He determined that negatively charged particles exist. -
Max Planck
He used quantization to prove how light is given off. He used radiation coming from an object that glowed to form energy. -
Robert Millikan
He proved how to find the charge of an electron in 1909. He conducted experiments to determine the electric charge carried by one electron. His experiment concluded that an electron’s mass is 1000 times smaller than the lightest atom. -
Ernest Rutherford
He discovered the nucleus and in 1920 he came up with protons to be positively charged particles. He also theorized the neutrons existence in 1920. -
Niels Bohr
He used hydrogen atoms to show the quantum theory. It proved energy only transfers in certain quantities. Electrons move around the nucleus. -
Erwin Schrodinger
He came up with the quantum model to distribute electrons in an atom using quantum numbers. It requires three quantum numbers to describe orbitals in an electron. -
Werner Heisenberg
He determined that a person cannot know the position and velocity of an electron at the same time. He discovered how to formulate quantum mechanics into matrices. He also contributed to the hydrodynamics theory and the atom’s nucleus. -
James Chadwick
He discovered that neutrons are in an atom's nucleus.
