Alkali Metals

Part of the Atomic Structure section of Coddy's Chemistry journey. Lesson 33 of 45.

The alkali metals are group 1 below hydrogen: Li, Na, K, Rb, Cs, Fr. Soft, kept under oil, they fizz in water, giving hydrogen gas and an alkaline solution.

Each has one outer electron and loses it to form a 1+ ion, like Na⁺. Down the group the outer electron is one shell further out and held more weakly: the first ionization energy falls from $520\ \mathrm{kJ/mol}$ (Li) to $419\ \mathrm{kJ/mol}$ (K).

Lithium, sodium and potassium as shells, each with one outer electron ringed, further out each time

Li, Na, K: one outer electron, one more shell each step down

The easier the electron goes, the more reactive the metal: reactivity rises down the group. Lithium fizzes; potassium bursts into flame.

Challenge

A teacher drops a small piece of lithium, sodium and potassium into three bowls of water. The metal that loses its outer electron most easily reacts fastest. Put the three in order of first ionization energy, the smallest first: that is also the most reactive first.

Try it yourself

Periodic tablePut the elements in order