Alkali metals
Alkali metals form group 1 (excluding hydrogen). They carry a single valence electron in the ns¹ orbital, which makes them among the most reactive elements in the table.
From lithium to francium, alkali metals are soft, highly electropositive and strongly reducing. They react vigorously with water, releasing hydrogen and forming basic hydroxides. Their oxidation state is exclusively +1 in practical chemistry.
Their density is remarkably low (lithium floats on oil, sodium on water) and their melting points decrease with atomic number. They are stored under mineral oil in the lab because air oxidation is almost instantaneous.
Applications: lithium batteries (Li, the energy transition), urban yellow street lighting (Na vapour), agricultural potash (K), atomic clocks and GPS (Cs, Rb), radioactive tracers (Fr — extremely rare and unstable).