-
500 BCE
The Alchemists
The Alchemists' goal was to change regular items into gold. They believed in four basic elements that could change into each other with chemical reactions. They ended up discovering a lot of elements and created some important tools. Alchemy has a long history and no exact range of dates. -
440 BCE
Plato
He believed that atoms were formed from triangles. He also thought that the four basic elements had different base shapes. A tetrahedron was fire, an octahedron was air, a cube represents earth, and an icosahedron represents water. -
400 BCE
Democritus
He created the theory of atomism, and he came up with the term atom. -
Robert Boyle
He created Boyle's Law which states that a volume of a gas decreases with increasing pressure and also said that the opposite is true. He also defined what an element is. -
Antoine Lavoisier
He created The Law of Conservation of Mass, it stated that if substances change state or form, they will keep the same mass. He also realized oxygen's role in combustion. -
Billiard Ball Model
The Billiard Ball Model was made by John Dalton. His model said that atoms were small indivisible spherical objects, and that atoms of the same element were identical. -
John Dalton
He said everything is made of atoms, atoms from the same element are identical, and chemical compounds are combinations of elements. -
Amedeo Avogadro
He distinguished the difference between a molecule and an atom. He also said how at the same temperature and at the same pressure different gasses with the same volume will have to same amount of molecules. -
Dmitri Mendeleev
He created the periodic table of elements -
JJ Thompson
He discovered the electron which showed that atoms are made up of smaller particles. -
Pierre and Marie Curie
They discovered polonium and radium. They also were able to confirm that radioactivity depends on the atoms, not the arrangements. -
Plum Pudding Model
The Plum Pudding Model was made by J. J. Thompson. He said that the atom was a sphere with a positive charge, and it had negative electrons inside it. This was his attempt to try and explain why atoms have no net electric charge. -
Albert Einstein
He mathematically proved that atoms actually exist. -
Robert Millikan
He was able to measure the electric charge of an electron. -
Ernest Rutherford
He said how atoms have a small dense nucleus that have electrons orbiting around it. -
Niels Bohr
He proposed an atom model that was different from Rutherford's. He said that electrons orbit the nucleus at certain distances, and they can only be at certain energy levels. -
Solar System Model
The Solar System Model was made by Niels Bohr. It showed that the atom is made of a nucleus with some electrons orbiting around, similar to a solar system. -
Henry G. J. Moseley
He said how the atomic number is the number of positive charges in the nucleus, and how major properties of elements are determined by atomic number and not by atomic weight. He also identified gaps in the periodic table. -
Erwin Schrödinger
He said that the behavior of subatomic particles are controlled by the laws of quantum mechanics which are different to the regular laws of physics. -
Electron Cloud Model
The Electron Cloud Model was made by Erwin Schrödinger. It shows the most probable location of electrons. You don't know for sure exactly where electrons are but they're more likely to be in certain places -
James Chadwick
He discovered the neutron.