Aluminium is used to make aeroplanes - 

because it is malleable and light.

Iron is used to make bridges - 

because it is strong and cheap.

Gold is used to make jewellery - 

because it is shiny and unreactive.

Copper is used in electrical circuits - 

because it conducts electricity and is ductile.

lithium - 

floats, moves slowly and fizzes

sodium - 

floats, moves quickly, ignites with an orange flame

potassium - 

floats, moves very quickly, ignites with a lilac flame

rubidium - 

almost instant violent production of white and orange sparks

lithium + water → - 

lithium hydroxide + hydrogen

sodium + oxygen → - 

sodium oxide

sodium + water → - 

sodium hydroxide + hydrogen

rubidium + oxygen → - 

rubidium oxide