He discovered the atom during 400 BCE, 60 years into his life.

Democritus lived from 460 BCE to 370 BCE. He believed that atoms were hard, solid, and unable to be compressed. In his philosophy, atoms existed within one's perception and soul, as well as matter.

Democritus proved the atom's existence by dividing a seashell into the smallest part possible. Atomism is a concept made by Democritus stating that all matter is made of atoms, which are unbreakable in nature.

-In 897, He discovered the electron and the went on to propose a model for the structure of the atom.

-When he created the model of atom structure in 1900

-the model name is plum pudding

He discovered that there are two types of radiation, alpha and beta particles. In 1899, he studied the absorption of radioactivity by thin sheets of metal foil.

Ernest Rutherford found that the atom consists mostly of empty space, with its mass concentrated in a central positively charged nucleus. He used a beam of alpha particles was aimed at a piece of gold foil. Most alpha particles passes through the foil, but a few were scattered backward. This showed that most of the atom is empty space surrounding a tiny nucleus.

He also suggested that instead of buzzing randomly around the nucleus, electrons inhabit orbits situated at a fixed distance away from the nucleus.

Dalton's atomic theory suggested that all matter was comprised of indivisible and indestructible atoms with distinct masses and properties, the combination of which determined the physical nature of their constituent elements.

The five main points are:

• Matter is made up of atoms, small and indivisible particles.

• All atoms of the same element are identical and have the same mass.

• Atoms of different elements vary in size, mass, and chemical behavior.

• Chemical compounds are made up of at least 2 atoms of different elements.