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440 BCE
Plato
Plato theorized that solid forms of matter are composed of indivisible elements shaped like triangles. -
400 BCE
Democritus
He believed all things were made of uniform and indestructible things called atoms, derived form the Greek word word "atomos", meaning indivisible. -
1500
The Alchemists
They believed all metals were created from two main elements, mercury and sulfur, in various proportions. -
Robert Boyle
He believed everything was composed of very tiny particles (atoms) and called this idea "atomism". -
Antoine Lavoisier
He established the law of conservation which states in a chemical reaction, matter is neither created or destroyed. -
John Dalton
He was an English chemist, physicist, and meteorologist. He stated that all matter is made of atoms that cannot be divided, created, or destroyed. -
Billiard Ball Model
This model was proposed by John Dalton and shows atoms as small, dense spheres with no internal parts. -
Amedeo Avogadro
An Italian scientist who proved equal volumes of gas contain equal numbers of electrons. -
Dmitri Mendeleev
He laid out the Periodic Table using the 70 known elements at the time using their atomic weight. -
J.J. Thompson
His experiments proved all atoms contain electrons, or negatively charged subatomic particles. -
Pierre and Marie Curie
They discovered the highly radioactive elements polonium and radium. -
Plum Pudding Model
This model was created by J.J. Thompson and showed electrons inside a sphere of positive charge. -
Albert Einstein
He mathematically proved the existence of atoms, and predicted both the size of atoms and molecules. -
Robert Millikan
His work proved that electrons have fixed, measurable charge that does not vary. He published his results in 1913. -
Ernest Rutherford
He described the atom having a nucleus, and stated the mass of the atom is concentrated in the nucleus. -
Neils Bohr
A Danish physicist who explained that electrons move in fixed orbitals. He received a Nobel Prize for his findings. -
Solar System Model
This model was developed by Neils Bohr and shows the electron "orbiting" the nucleus of the atom. -
Henry G. J. Mosely
He published a paper in which he concluded that the atomic number is equivalent to the number of positive charges in the atomic nucleus. -
Werner Heisenberg
He discovered the uncertainty principle which states that a particle's momentum and position cannot be known exactly. -
Erwin Schrodinger
He was an Austrian physicist who formulated a wave equation to accurately calculate energy levels of electrons in atoms. -
Electron Cloud Model
It was developed by Schrodinger and Heisenberg. It showed represents the area around the nucleus where atoms can be found. -
James Chadwick
He was awarded a Nobel Prize for his discovery of the neutron.