proton vs electron

The core difference

• proton — positive charge, in the nucleus, mass roughly 1 atomic mass unit.
• electron — negative charge, outside the nucleus, mass about 1/1836 of a proton.

A neutral atom has equal numbers of each, so the charges cancel.

What each one determines

• The number of protons defines which element an atom is. Change it and you have a different element — that is what nuclear reactions do.
• The number of electrons determines chemical behaviour: bonding, reactivity and almost everything chemistry studies.
• The number of neutrons gives the isotope — same element, different mass.

So protons decide identity, electrons decide behaviour.

Ions

Atoms gain or lose electrons, never protons, in ordinary chemistry. Lose an electron and the atom is left positive — a cation. Gain one and it becomes negative — an anion. Protons are locked in the nucleus and only move in nuclear processes.

Scale

Almost all of an atom's mass is nuclear, and almost all of its volume is empty space occupied by the electron cloud. If a nucleus were a marble, the atom would be measured in hundreds of metres.

The names

Electron was coined in 1891 from the Greek for amber, elektron — amber having been the substance that produced static electricity when rubbed, giving us electricity itself. Proton was named later, from the Greek for "first".