The lightest 'non-metal' could be Hydrogen and Helium! Both are gases, and therefore, not a metal.
The lightest metal is lithium.
Lithium is the lightest.
Cobalt.
Helium
Lithium is the lightest metal, Potassium is the second lightest -- density about 0.86 kg/L
Lithium is the lightest element metal with a relative atomic mass of 7 (3 protons, 4 neutrons).
Lithium is the lightest metallic element. Its atomic weight is 6.491.
Alluminum is probably the lightest of coinage metals used to-date.
Lithium is a soft white alkali metal that is the lightest metal under standard conditions. It is also the least dense solid element.
With a density of 0,534 g/cm3 lithium is the lightest between metals.
Lithium