alkali metals (Group 1)

If you have seen the classic chemistry demonstration where a pea-sized lump of metal dropped into water skitters, fizzes, and bursts into lilac or yellow flame, you have met the alkali metals. They are the six elements of Group 1 below hydrogen: lithium, sodium, potassium, rubidium, caesium, and the rare radioactive francium. They are so reactive that you never find them as free metals in nature, and they are so soft that sodium and potassium can be cut with a knife like cold butter.

Each alkali metal has a single electron in its outermost s shell, sitting far from the nucleus and shielded from it by all the inner electrons, so it is held very loosely. Losing that one electron gives a stable noble-gas configuration and a +1 ion, and the metals do this eagerly — they have the lowest ionization energies and the most negative reduction potentials in their periods. This single, easily lost electron explains everything about them: they are the most electropositive, the softest and lowest-melting of metals (the lone bonding electron makes a weak metallic bond), and they react violently with water to give a hydroxide (an alkali, hence the name) plus hydrogen gas, as in 2 Na + 2 H2O giving 2 NaOH + H2.

These metals are central to inorganic chemistry and to life. Sodium and potassium ions run the electrical signalling of nerves and muscles; lithium compounds treat bipolar disorder and power batteries; sodium hydroxide and sodium carbonate are bulk industrial chemicals. The honest caveats: their reactivity rises down the group (caesium reacts explosively with water), and lithium, the smallest, is the odd one out whose chemistry partly resembles magnesium rather than its own family — the diagonal relationship.