The Atom

Atoms

The basic building blocks of matter, comprised of protons, neutrons, and electrons.

Protons

Positively charged particle in the nucleus.

Neutron

Neutral particle in the nucleus.

Electron

Negatively charged particle that orbits in outer shells around the nucleus.

Democritus’ atomic theory

Proposed that matter is composed of indivisible atoms, which combine in various ways to form different substances.

Dalton’s atomic theory

All matter is composed of tiny, indivisible particles called atoms, atoms of the same element are identical, atoms of different elements have different properties, and atoms combine in simple whole number ratios.

Thomson’s atomic theory

An atom is a sphere of positively charged matter with negatively charged electrons embedded within it (Plum Pudding Model).

Rutherford’s atomic theory

Proposes that an atom consists of a tiny, dense, positively charged center called the nucleus, surrounded by negatively charged electrons orbiting in empty space, with the nucleus containing nearly all of the atom’s mass.

Bohr’s atomic theory

Explained that electrons move in fixed orbitals (shells) and not anywhere in between, with each orbit having a fixed energy.