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500 BCE
The Alchemists
The Alchemists broke down the chemical composition of the four basic elements, which will later evolve into the periodic table. Also, developed a theory that states that it's possible to change base metals into gold. -
400 BCE
Democritus
Democritus was a Greek philosopher who first found and introduced the idea of the atom around 400 BC. -
400 BCE
Plato
Plato found out that there are five solid shapes whose sides are made from polygons and was convinced that atoms must develop from these 5 fundamental solids. -
Robert Boyle
Robert Boyle created Boyle's Law which stated that the volume of a gas is inversely proportional to the pressure of the gas. He also suggested that all substances were made up of atoms. -
Antoine Lavoisier
Antoine Lavoisier was a French chemist who discovered that the total mass of products and reactants in a chemical reaction will always be the same amount. -
John Dalton
John Dalton was a British chemist and physicist who developed the atomic theory and stated that all matter is made of atoms. He also, created the Billiard Ball Model. -
Billiard Ball model
Was created by John Dalton in 1803, to show us how he thought atoms looked and used a billiard ball as an example. -
Amedeo Avogadro
Amedeo Avogadro made an hypothesis that states that equal volumes of different gases, contains equal number of molecules. He was also the first one to know that elements could exist in the form of molecules. -
Dmitri Mendeleev
Dmitri Mendeleev found out all chemical elements are arranged in order of increasing atomic weight and developed the periodic classification of elements in 1869. -
J.J. Thompson
J.J. Thompson was the first to discover the electrons in the atom in 1897. -
Pierre and Marie Curie
Pierre and Marie Curie were French physicists who discovered the radioactive elements of Polonium and Radium. -
Plum Pudding Model
An historical scientific model of the atom created by J.J. Thompson in 1904 and shows electrons surrounded by a positive charge. It was also, The first model to represent the atomic structure of matter. -
Albert Einstein
Albert Einstein was a German physicist who proved mathematically the existence of atoms. -
Robert Milikan
Robert Milikan discovered that atoms have a positively charged nucleus and the positively charged particles inside the nucleus are called protons. -
Ernest Rutherford
Ernest Rutherford found out about the nucleus in 1911 and discovered that the atom is mostly empty space, with most of its mass in the nucleus. -
Neils Bohr
Neils Bohr proposed a theory for the hydrogen atom and was the first one to discover that electrons move around the nucleus. -
Henry G. J. Mosely
Henry G. J. Mosely discovered the Atomic Number in 1913 and concluded that the atomic number is the number of positive charges in the nucleus. -
Solar System Model
This model was created in 1913 and used to described an atom as a central positive entity (Sun/Nucleus) and going around the negative entities (Planets/electrons). -
Schrodinger
Schrodinger discovered the Schrodinger's wave equation which calculated the energy levels of electrons in 1926. -
Electron Cloud Model
Developed in 1926 by Erwin Schrodinger and states that we cannot know exactly where an electron is at any time. -
Werner Heisenberg
Developed a mathematical way of expressing the energy levels of electrons and developed a key piece of quantum theory in 1927. -
James Chadwich
James Chadwich proved and discovered the existence of neutrons in the atom in 1932
