Atoms of each element are represented by their own chemical symbol. A chemical symbol:
For example the symbol O represents an atom of oxygen, and Na represents an atom of sodium. You must write the chemical symbol of sodium as Na, not as NA, na or nA.
There are over 100 different elements. The names and symbols of the elements are shown in the periodic table. Elements are arranged into groups with similar properties. Groups are numbered from 1 to 7, then 0.
In the periodic table, metals are on the left of the stepped line, and non-metals are on the right.