The Development of Atomic Theory

The notions about atoms has begun since 2500 years ago. In year 400 BC, a Greek phiosopher named Democritus stated that substances are composed by very small and unseen particles. Democritus called them atomos, which in Greel language means 'unable to be divided'.

In 1806, John Dalton conducted an experiment concerning matters. Based on such experiment, Dalton concluded that matters are composed by small particles that can't be divided. Those particles then are called atoms. Dalton imagined that the shape of atoms were like small solid balls, much smaller than bilyatd balls and couldn't be divided.

Atomic model then continues  to develop from time to time, along with the discovering of atomic properties. J.J. Thomson, Ernest Rutherford, and Niels Bohr were the scientists who played important roles in the development of atomic theory.

J.J. Thomson (1856-1940) Stated that atoms contain electrons. By his experiement Thomson proved that atoms can still be devided. Ernest Rutherford then proposed the atomic core model. According to Rutherford, in the center of atoms there is atomic core which contain protons. This Rutherford theory was developed by Niels Bohr. Bohr's research shown that electrons circle the atomic core on different energy levels. The atomic model from Rutherford-Bohr is the only model that is accepted all over the world until present days.