Alkali metals (group 1)

One outer electron

Every alkali metal has a single outer electron in an s orbital, so its configuration ends in ns¹: lithium is [He] 2s¹ and sodium is [Ne] 3s¹. Losing that electron leaves the stable arrangement of the previous noble gas, so alkali metals easily form 1+ ions such as Li⁺, Na⁺ and K⁺. They are never found free in nature and are stored under oil in the lab.

Physical properties

Alkali metals are soft enough to cut with a knife, and a fresh, silvery surface tarnishes within seconds in air. Lithium, sodium and potassium are less dense than water, and melting points are low for metals, from about 180 °C for lithium down to 28 °C for cesium. Their compounds color flames: crimson for lithium, yellow-orange for sodium and lilac for potassium.

Reactions with water and other elements

All alkali metals react with water to form a hydroxide and hydrogen gas: 2Na + 2H₂O → 2NaOH + H₂. The hydroxide solution is strongly alkaline, which gives the family its name. Lithium fizzes steadily, sodium melts into a ball and darts across the surface, potassium bursts into a lilac flame, and rubidium and cesium react explosively.

They also combine directly with nonmetals, forming white ionic salts with chlorine (2Na + Cl₂ → 2NaCl) and oxides in air, for example 4Li + O₂ → 2Li₂O.

Trends down the group

Each step down the group adds an electron shell, so the outer electron is farther from the nucleus, better shielded and easier to lose. Reactivity therefore increases from lithium to cesium. Atomic radius increases, while first ionization energy and melting and boiling points decrease. Density generally rises, although potassium is less dense than sodium. Francium is hard to study: its longest-lived isotope has a half-life of only 22 minutes.

Uses of the alkali metals

Lithium powers the rechargeable lithium-ion batteries in phones and electric cars, and lithium carbonate is a medicine for bipolar disorder. Sodium is found in table salt (NaCl), baking soda (NaHCO₃) and the sodium hydroxide used to make soap. Potassium is an essential nutrient and a major ingredient of fertilizers, and cesium atomic clocks define the second.