Uses

Lithium's low density and reactivity make it valuable in alloys — with lead for the "white metal" bearings used in motor engines, with aluminium for aircraft components, and with magnesium for armour plating — besides its role in thermonuclear reactions and in electrochemical cells (batteries).

Sodium is alloyed with lead to manufacture the organolead compounds $PbEt_4$ and $PbMe_4$, historically used as anti-knock additives in petrol (a use now abandoned in favour of unleaded fuel); liquid sodium metal also serves as a coolant in fast breeder nuclear reactors, thanks to its high thermal conductivity and low melting point. …