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430 BCE
Democritus
Democritus said everything was composed of atoms and were constantly moving. He also claimed they are infinite in number and indestructible. -
Law of Conservation of Mass
This law claimed that matter is not created nor destroyed in a closed system. -
Antoine Lavoisier
Lavoisier discovered matter was composed of atoms that aren't created or destroyed during chemical reactions. -
Alchemists
Alchemists believed that all metals were made up of mercury and sulfur. -
Law of Definite Proportions
This law claims every chemical compound has a set proportion of the elements it contains. -
Dalton's Atomic Theory
Dalton's theory said all matter is made up of atoms. These atoms are indivisible. -
John Dalton
Dalton's theory had 3 parts, all matter is made of atoms, all atoms of a given element are identical in mass and properties, and compounds are combinations of two or more different types of atoms. -
Joseph Louis Proust
Proust suggested all matter was composed of tiny indivisible particles, called atoms. He also created the Law of Definite Proportions. -
Dmitri Mendeleev
Mendeleev found that when all known chemicals are arranged in order by increasing atomic weight there is a pattern. The pattern has periodicity within the groups of elements. -
J.J. Thomas
Thomas discovered the electron, disproving the theory that atoms were the smallest particle to exist. -
Cathode Ray Tube
The Cathode Ray Tube experiment proved the ray was composed of negatively charged particles. Then that these particles must exist as part of atoms found in every element. -
Plum Pudding Atomic Model
This model gave the theory that claimed the atom had a negatively charged electrons with a positive "soup" around. -
Robert Millikan
Millikan confirmed the existence of the electron and determined it's charge. -
Oil Drop Experiment
This experiment determined that electrons have mass and a specific charge. -
Gold Foil Experiment
The Gold Foil experiment proved the atom has a positively charged nucleus. This nucleus is tiny, dense, and mostly empty space. -
Nuclear Model
Rutherford's nuclear model showed there is a nucleus inside an atom, the electrons are distributed around this nucleus. -
Ernest Rutherford
Rutherford conducted the gold foil experiment showing that an atom is a mostly empty space surrounded by a nucleus. -
Planetary Model
The Planetary model's theory claimed electrons travel in orbits, circling the nucleus. -
Niels Bohr
Bohr proposed a theory for the hydrogen atom, that some physical quantities only take discrete values. -
Henry Moseley
He published a paper in which he concluded that the atomic number is the number of positive charged in the atoms nucleus. -
Erwin Schrodinger
Schrodinger claimed the behavior of an electron within its atom can be explained by treating them mathematically as a matter of waves. -
Quantum Mechanical Model
This model is based on quantum theory, claiming matter has wave-like properties. -
Werner Heisenberg
Heisenberg discovered the theory that a particle's position and momentum can't exactly be known. -
James Chadwick
Chadwick discovered the neutron and that it weighs 0.1% more than a proton.