science-subject-for-high-school-9th-grade-chemistry (1)

Atom

The smallest particle of an element and the smallest amount of a substance that can take part in any chemical reaction.

Democritus

Greek philosopher who first proposed the concept of the atom, naming the smallest piece of matter 'ATOMOS' meaning 'not to be cut.'

John Dalton

An English chemist who proposed that all elements are composed of atoms and that atoms of the same element are exactly alike.

J.J. Thomson

An English scientist who discovered the electron and proposed the 'Plum Pudding' model of the atom.

Ernest Rutherford

An English physicist who theorized that positively charged particles are contained in the nucleus of an atom.

Niels Bohr

A Danish scientist who improved atomic theory by placing electrons in specific energy levels, resembling the solar system.

Arnold Sommerfeld

A German physicist who modified Bohr's atomic theory to include elliptical orbits for electrons.

Erwin Schrödinger

Considered the Father of Quantum Mechanics, proposed that electrons behave as waves and do not have defined paths.

Electron

A negatively charged particle that orbits the nucleus of an atom.

Quantum Mechanical Model

Current model of the atom where electrons are found in regions of probability rather than fixed orbits.