The Periodic Table

Democritus and Leucippus

440 BCE

These two scientists were the first propose an atomic theory. This theory helped the scientists form a new model of the atom called a hard sphere model. The model proposed that atoms were solid that makes up all matter.

John Dalton

1808

John Dalton proposed his own atomic theory that an atom is a small particle that consists of masses and properties based on its element.
He also states that an element consists of only one type of atom, but each element is different.

Johann Dobereiner

1817

This scientist organized the periodic table by the Law of Triads. This law stated that there was a connection between the atomic weights and elements, which was in group of three.

John Newlands

1864

This scientist proposed the periodic table by the Law of Octaves. This law states that there was a pattern with properties every 8th element when the elements were organized by their atomic weight.

Dmitri Mendeleev

1869

This scientist organized the periodic table by order of elements' atomic weight to identify the pattern of their properties. This organization proves that it has a pattern to predict the elements of the periodic table.

JJ Thompson

1906

This scientist proposed an atomic theory that atoms consist of small particles called electrons. These electrons will have a negatively charge. He then created a plum pudding model that was based on his atomic theory.

Ernest Rutherford

1911

This scientist proposed an atomic theory that an atom is mostly empty space but has a dense positively charged center called a nucleus. He then performed a experiment called the gold foil experiment, which used a gold metal foil with particles that bounced or deflected back. The result of this experiment showed that JJ Thompson model was incorrect and false.

Neils Bohr

1913

This scientist proposed an atomic theory that an atom consists of electrons on different energy levels orbiting the nucleus. This theory helped him invent the Bohr model, which shows which energy level each electron is on.

Henry Moseley

1913

Henry proposed that the periodic table should be arranged in order of an elements atomic number to get rid of the problems from previous organization methods. This was based on the Modern Periodic Law. It was then organized by their properties due to the arrangement of increasing atomic number, which we end up using today on the Periodic table.

Sir James Chadwick

1932

This scientist discovered that the positively charged particles in the nucleus of an atom is called neutrons. He then used an experiment similar to the gold foil experiment to support his discovery.
The Atomic Song