History Development of Atomic Model

400 BC - Democritus

400 BCE

That all matter is alternatively formed of different tiny, solid and unbreakable particles. Additionally, he found that the properties of these particles also determined the properties of matter. He was the first to use the term ‘atomos’ coming from the word ‘atom’.

1807 - John Dalton

1807

That each element consists of its own brand of invisible atoms, which are very unique. He also assigned atomic weights to the atoms, only of the 20 he knew.

1903 - JJ Thompson

1903

He had discovered that atoms were also made up of smaller components. He referred to the components as "corpuscles”, which are now known as electrons.

1911 - Ernest Rutherford

1911

Development of the nuclear model of an atom. This model showed that most of the mass is contained in a small positive nucleus, surrounded by negative electrons.

1913 - Niels Bohr

1915

Electrons can only travel around the nucleus on certain pathways, or orbits, similar to planets. Because of this, it was often called the planetary model.

1932 - James Chadwick

1932

James Chadwick discovered neutrons. This proved that in the nucleus, there weren’t just positively charged molecules, but negative as well.