An atom is the smallest part of an element that can take part in a chemical change.
The word “atom” comes from the Greek “atomos”, which means “unable to be cut”.
Atomism is the philosophy of the existence of atoms. The first theories of atoms come from India. There was a Hindu sage named Kanad that hypothesized that all mater was composed of earth, water, light, wind, ether, time, space, mind and soul. Then another philosopher named Pakuda Katyayana suggested that everything can be classified as earth, water, fire, air, pleasure, pain and soul.
As a result, Indian atomists concluded how atoms could combine, react and move. They also suggested that they could obtain energy by splitting these particles.
After the Indians, there was a Greek philosophers Democritus and Leucippus, who said that all atoms were made of the same material but different shapes and sizes. Then an Islamic philosopher took both the Indian and the Greek theories and suggested that there could be particles smaller than atoms.
In the 1800s, John Dalton considered previous theories, who proposed that atoms of a particular element were the same size and weight. By 19114, the theory that contributed most to our knowledge of the structure of the atom was by Ernest Rutherford.
There are more atomists such as J.J. Thomson, Niels Bohr, James Chadwick, Marie Curie and Henry Moseley.
An atom contains three subatomic particles, which are protons and neutrons that are found at the center of the nucleus and around the nucleus there are electrons.
There are many atomic models corresponding with the theories.
Democritus
"Nothing exists except atoms and empty space; everything else is opinion." –Democritus
*Democritus was the first person ever to propose that matter was made of atoms, and that they are indestructible. He also theorized that they are, always have been and always will be, in motion. Democritus thought that the solidness of a substance would determine with the shape