HYDROGEN Symbol: H Atomic number: 1 A very light element and the most abundant element in the universe.

HELIUM Symbol: He Atomic number: 2 A gas used in some balloons because it is less dense than air.

CARBON Symbol: C Atomic number: 6 Found in materials including graphite and diamond; both are forms of carbon.

OXYGEN Symbol: O Atomic number: 8 Makes up about 21% of Earth's atmosphere and is needed for respiration.

SODIUM Symbol: Na Atomic number: 11 A reactive metal; in table salt it is chemically bonded to chlorine.

CHLORINE Symbol: Cl Atomic number: 17 A reactive element used to disinfect some water supplies and pools.

IRON Symbol: Fe Atomic number: 26 A useful metal in steel; iron is also present in haemoglobin in blood.

GOLD Symbol: Au Atomic number: 79 A metal valued for jewellery; it resists corrosion in ordinary conditions.