Chemical Symbol
A one or two letter shorthand used to represent one atom of an element. The first letter is always a capital, and the second — if there is one — is always lowercase.
Examples: H for hydrogen, O for oxygen, Na for sodium, Fe for iron, Ca for calcium.
Exam note: Some symbols come from Latin names — Na from Natrium, Fe from Ferrum, Cu from Cuprum, Pb from Plumbum. These are frequently tested.
Chemical Formula
A combination of chemical symbols and numbers that shows the type and number of atoms in one unit of a substance. Numbers written below the line — called subscripts — show how many atoms of each element are present.
Examples: H₂O means 2 hydrogen atoms and 1 oxygen atom. H₂SO₄ means 2 hydrogen, 1 sulphur and 4 oxygen atoms.