Ionisation

If the number of electrons is equal to the number of protons then the atom is uncharged and is electrically neutral.

However, atoms can gain or lose electrons: increasing or decreasing the negative charge.

Ionisation is the addition or removal of an electron to create an ion.

Losing an electron creates a positive ion.

Gaining an electron creates a negative ion.

An atom's charge can only change through gaining or losing electrons. Protons cannot be added or removed because they are bound up with neutrons in the nucleus.

Electrons can be lost because an ionising radiation (something that you will study later in this chapter) comes close to or collides with the atom and forces the electron away from the atom.

Example

Carbon atom with six electrons orbiting a nucleus of six protons and six neutrons. There are two electrons in the inner level and four in the outer level.Carbon atom with six neutrons, six protons and six electrons

If the atom is hit by an ionising radiation, it may lose an electron.

This turns the atom into a positively charged ion - it has more protons than electrons.

Carbon ion with six electrons orbiting a nucleus of six protons and six neutrons. There are two electrons in the inner level and three in the outer level, with the missing one labelled.Carbon ion with six neutrons, six protons and five electrons