Monatomic & polyatomic ions

Define the terms ‘monatomic’ and ‘polyatomic’ in terms of anions and cations.

Monatomic: anion(-)/cation(+) that consists of a single charged atom.

created when an atom gains or loses an electron.

anions name change to -ide

Polyatomic:

anion/cation that consists of a charged molecule (or group of atoms).

created when a molecule gains or loses electrons.

• If ion has oxygen, name is changed to ‘-ate’, e.g sulphate is SO42-.

• If similar form but one less oxygen, name ends with ‘-ite’, e.g sulphite is SO32-.

• If similar form that has a hydrogen atom before it, the word ‘hydrogen’ is written before it, e.g hydrogen sulphate is HSO4- and hydrogen sulphite is HSO3-.

  • Note: that when a hydrogen is added, the charge of the anion increases by ‘+1’.