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440 BCE
Plato
Discovered that atoms broke down mathematically into triangles. He was a student of Socrates. -
430 BCE
Democritus
Discovered that atoms are without pores and entirely fill up the space they occupy. He saw the void as vacuum- an infinite space with an infinite number of atoms. -
122 BCE
The Alchemistis
Discovered that particles are in constant motion.
Discovered that no matter could be eternal, as no matter can come from nothing -
1543
Solar System Model
By Nicolaus Copernicus. Illustrates the relative positions and motions of the planets and moons. -
Robert Boyle
Discovered that matter is made up of tiny particles. He discovered the relationship between pressure and volume in gas. -
Antoine Lavoisier
He named and recognized 33 substances to be considered elements including oxygen and hydrogen. Discovered that combustion was a reaction of metal or organic substance with common air. -
Billiard Ball Model
Proposed by John Dalton in the early 1800s. He thought that atoms were the smallest particles of matter. -
John Dalton
Discovered that compounds are combinations of two or more different types of atoms. His theory was based on the law of conservation of mass and the law of constant composition. -
Amedeo Avogadro
He proposed Avagadro's Law equal volumes of gasses at equal temperature and pressure contains the same number of particles. Italian physicist and mathematician. -
Dmitri Mendeleev
Known for his discovery of periodic law- elements are arranged in order of increasing atomic weight. He was a Russian chemist and inventor. -
Pierre and Marie Curie
Discovered polonium and radium. Coined the term radioactivity and created a new field of study called atomic physics. -
JJ Thomson
He had the earliest description of the inner structure of atoms. He thought that atoms were uniform spheres of positively charged matter in which electrons are embedded. He headed the Cavendish Laboratory at Cambridge. -
Plum Pudding Model
By JJ Thomson. Negatively charged particles swim in a positively charged sea. -
Albert Einstein
Discovered that electrons could leave metal through the usage of light. He mathematically proved the existence of atoms and their random ceaseless motion. -
Robert Millikan
He determined the electric charge of a single electron. Conducted the Oil Drop experiment. -
Ernest Rutherford
Discovered that all the atoms mass is concentrated in the center and all the electrons revolve around it. He was known as the father of nuclear physics. -
Niels Bohr
Created a model of the atom that describes electrons as revolving in discrete orbits around a positively charged nucleus. He was the first to discover that electrons travel in separate orbits and that the electrons in the outer orbit determine the properties of an element. -
Henry G.J. Mosely
He demonstrates the major properties of an element are determined by the atomic number not the atomic weight. He experimented with x rays of certain periodic table medals. -
Electron Cloud Model
Proposed by Erwin Schrodinger in 1926. Electrons were no longer depicted as particles moving around a central nucleus in a fixed orbit. -
James Chadwick
He discovered the neutron, and that the nucleus contains both positively and negatively charged protons and neutrons, which have the same mass. His discovery led to straight to the development of the atomic bomb.