Scientists That Contributed to the Atomic Theory

Democritus´s Discovery

442 BCE

All atoms are small, hard, invisible and indestructable particales made of a singe material formed in different shapes and sizes. His model, which is named after him, is a simple round sphere with no elecrons, protons or neutrons.

Aristotle's Theory

340 BCE

-After the atomic theory was discovered, Aristotle didn't believe in it. He theorized that everything was made of either fire,water,air, earth, and aether. This theory was proven incorrect because there were more elements discovered later on. He contributed to the atomic theory but in a negative way.

Dalton Discovery

1803

-He said that every form of matter was made up of small individual particles
-Dalton Model: all elements are composed of atoms can't be divided or destroyed. All elements of same element are alike. Atoms of different elements are different. Different atoms combine to form compound.

Thomson Discovery

1894

Determined that all matter is made up of tiny particales that are much smaller than atoms, he called them "Corpuscles" but its now called electrons. His model, also named after him, states that the atom is composed of electrons surrounded by a soup of positive charge to balance the electrons negaative charge.

Rutherford's Discovery

1907

-He discovered that nearly all the total mass of an total mass of an atom is in the nucleus. He was named father of the nuclear age.
-Rutherford Model: Electrons travel in a defined circular path around a set nucleus.

Bohr Discovery

1922

-He asserted that physical properties on an atomic level would be viewed differently depending on experimental parameters.
-Bohr Model: electrons traveling defined circular path around a set nucleus

Chadwick Contribution

1932

He discovered a previously unknown particle neutron in the atomic nucleus. He had no complete model of his own, but improved the model of Rutherford, adding protons and neutrons to the nucleus.