Alkali metals. Sodium and potassium

The main subgroup of group I — Li, Na, K, Rb, Cs, Fr — are called alkali metals because their hydroxides are strong alkalis. All have a single s-electron in the outer shell (ns¹), so they are s-elements; for example Na is [Ne]3s¹ and K is [Ar]4s¹. Down the group the nuclear charge, the number of shells and the atomic radius increase, the outer electron is held more weakly and the ionisation energy falls, so metallic and reducing character grow: the most active naturally available alkali metal is caesium (francium is an extremely rare radioactive element). In all compounds they show the +1 oxidation state. Alkali metals are soft, light and low-melting: lithium melts at about 181 °C and caesium at about 28 °C; lithium is the lightest metal (density ≈ 0.53 g/cm³). Sodium and potassium are essential for living organisms: Na⁺ and K⁺ ions are needed for the potassium–sodium pump of cell membranes, nerve impulses and heart function; a 0.9 % NaCl solution is used in medicine as physiological saline. Potassium salts (KCl, K₂SO₄, KNO₃) are fertilisers and lithium is used in batteries. In Uzbekistan potassium salts are mined at deposits such as Tyubegatan and Khojaikon, and table salt at Khojaikon, Borsakelmas and others.