Group 1: hydrogen and the alkali metals

One outer electron: the ns¹ pattern

Each configuration ends in ns¹, where n is the period number: hydrogen is 1s¹, lithium [He] 2s¹ and cesium [Xe] 6s¹. The metals give that electron away easily, leaving a noble gas core, so they form 1+ ions such as Li⁺, Na⁺ and K⁺.

Hydrogen has no inner core to fall back on. It usually shares its electron, as in H₂ and H₂O, but it can also lose it to become H⁺, the ion that makes acids acidic, or gain one to form the hydride ion H⁻, as in lithium hydride (LiH).

Trends down the column

Each step down adds a shell, so the outer electron sits farther from the nucleus and is easier to remove. First ionization energy falls from 13.598 eV for hydrogen to 5.392 eV for lithium and 3.894 eV for cesium, and electronegativity from 2.2 to 0.98 and 0.79, so the metals near the bottom react most violently.

Melting points fall too: lithium melts at 453.65 K, sodium at 370.94 K and cesium at just 301.59 K, about 28 °C, while hydrogen melts at 13.99 K.

Where you meet group 1

Hydrogen is in water and most of the molecules in your body, and huge amounts go into making ammonia for fertilizer. Sodium and potassium ions carry the signals in your nerves, lithium stores energy in phone and car batteries, and rubidium and cesium keep time in atomic clocks.

Group 1 versus the alkali metals

A group is a column, while a family is a set of elements that behave alike. Hydrogen is in the column but not the family: it forms covalent bonds rather than ionic ones, and some tables place it above fluorine instead. Deep inside Jupiter, though, crushing pressure is thought to turn it into a liquid metal. The six metals below it have their own alkali metals family page.