The History of Atomic Theory

Atom

The basic unit of a chemical element, made up of protons, electrons, and neutrons.

Atomic Mass

The weight of an atom, usually expressed in atomic mass units (amu).

Atomic Number

The number of protons in the nucleus of an atom; it is unique for each element and determines the element's position in the periodic table.

Democritus

A Greek philosopher who theorized that matter is made of small, indivisible particles called atoms.

Atomos

The term meaning 'not to be cut,' representing the smallest unit of matter as proposed by Democritus.

Dalton's Atomic Theory

A theory that outlines 5 postulates regarding the nature of atoms, including that all matter is made of atoms and they cannot be created or destroyed.

Postulate

A statement taken to be true for the purposes of argument or investigation.

Thomson's Plum Pudding Model

An atomic model proposing that atoms consist of a positively charged substance with negatively charged electrons scattered throughout.

Cathode Rays

Streams of negatively charged particles observed in vacuum tubes, leading to the identification of electrons.

Indivisible Particles

The concept that atoms are the smallest unit of matter and cannot be divided into smaller pieces, proposed by Democritus.