John Dalton discovered in 1803 that atoms of different elements in simple whole numbers to create compounds. Atoms can not be created or destroyed.

Democritus

492 BCE

The Democritus said that everything is composed of atoms, but between atoms lies space, and that atoms are indestructible.

Plato

427 BCE

Plato did not believe in the atom theory. He believed all matter was made up of the four elements which are Fire ,Earth, Air and water.

The Alchemists

500

The alchemists started looking more into Aristotle theory. The goal was to change the structure of the atom, but they failed to turn common items into gold. They did create a scientific process which allowed to go into more depth of the atom.

Robert Boyle

1660

Boyle believed that chemistry could be explained through the motion of atoms.

Lavoisier

1778

Lavoisier is known for his discovery on how oxygen plays a role in combustion. He recognized and named oxygen and Hydrogen.

John Dalton

1803

John Dalton discovered that atoms of different elements in simple whole numbers to create compounds. Atoms can not be created or destroyed.

Dmitri Mendeleev

1869

Dmitri first contributed in the first periodic table of elements. He described chemical elements based on atomic weight and valency.

Aristotle

1885

Aristotle was not a scientist, he was a philosopher. He believed everything was a combination of fire,earth,water and air. His theory was that a mass of incomprehensible size was everywhere; he called this 'hyle'.

The Curies

1896

The Curies discovered the existence of the elements radium and polonium in their research Pitchblende. They found extra radiation by considering uranium alone.

JJ Thomson

1897

Thomson is credited with the discovery of an electron. The negatively charged particle in an atom.

Ernest Rutherford

1899

Ernest discovered the nuclear structure of the atom Ernest determined that there were different types of radiation. From there he figured out helium gas could be formed into radioactive substances.

Albert Einstein

1905

Albert founded the mass-energy equivalence formula, which became one of the most famous equation. He also came up with any liquid is made up of mass.

Robert Millikan

1908

Robert is well known for his oil drop experiment. Which confirmed the existence of an electron and was certain with the charge.

Henry G.J. Mosely

1914

Mosely is well known for his contribution to the atomic number based on Neil Bohrs theory. He came up with his own experiment called Mosely's law in the X-ray spectra.

Neils Bohr

1920

Neils Bohr was the first to discover that electrons travel separately around the nucleus. Also that the number of electrons determine the properties of an element.

Werner Heisenberg

1932

Werner contributed to the atom because he formulated quantum mechanics and discovered the uncertainty principle, which states that a particle’s position and momentum cannot both be known exactly.