Chemical symbols

Each element is represented by its own chemical symbol. A chemical symbol:

  • consists of one or two letters
  • always starts with a capital letter, with any other letter in lower case

For example, the element mercury is shown as Hg. You must not show it as HG, hg or hG.

The periodic table shows the names and/or symbols of the elements. Elements are arranged into groups that share similar characteristics. Groups are numbered from 1 to 7, then 0.

Note that in the periodic table, metals are found on the left and non-metals are found on the right.

Period table with metals in red and non-metals in yellow.Each box in the periodic table contains the chemical symbol for an element


An ion is a charged particle formed when an atom, or a group of atoms, loses or gains electrons. The number and sign of its electrical charges are shown in superscript text.

Names and formulae of some common ions:

Name of ionIon formulaElectrical charge(s)
SodiumNa+One positive
MagnesiumMg2+Two positive
ChlorideCl-One negative
OxideO2-Two negative