Atoms and Molecules

An atom is the smallest particle of an element. It is made up of: protons, neutrons and electrons.

Protons

-Symbol: p

-Has a relative mass of 1

-Has a positive charge

Neutrons

-Symbol:n

-Has a relative mass of 1

-Has a neutral charge (0).

Electrons

-Symbol: e

-Has a relative mass of 1/2000

-Has a negative charge

The nucleus of the atom consists of protons and neutrons. The total number of neutrons and protons is called the nucleon number. Electrons move around the nucleus in fixed orbits.

The number of protons and electrons are actually the same (for example, if the atom has 8 protons, you will know it has 8 electrons). To determine the number of neutrons, subtract the proton number from the mass number to know the number of neutrons the atom has (for example, if the proton number is 17 and there are 8 protons, the number of neutrons is 9).