Group 1 — the elements that give their electron away to almost anything
Six soft, silvery metals so eager to lose their single outer electron that none of them is ever found free in nature. They are stored under oil, cut with a knife, and react with water violently enough to set the hydrogen they release on fire.
Highlighted in the periodic table
Every member
What defines them
Every alkali metal has exactly one electron in its outermost shell, and it sits far from the nucleus behind a full inner shell. Losing it produces a stable noble-gas core, so they lose it at the slightest excuse — forming +1 ions in essentially every compound they make.
Lithium fizzes in water. Sodium skitters and may ignite. Potassium ignites reliably, with a lilac flame. Rubidium and caesium explode on contact. The trend is straightforward: the further the outer electron sits from the nucleus, the less it is held, and the faster it goes.
They are soft enough to cut, light enough that lithium, sodium and potassium float on water, and low-melting — caesium liquefies at 28 °C, barely above room temperature. One weak metallic bond per atom does not hold a lattice together well.
Periodic trends
Down the group: atomic radius grows, ionisation energy falls, density rises (except potassium, which is lighter than sodium), melting point falls, and reactivity climbs steeply. Across a period they are the largest atoms and the lowest ionisation energies of all.
In the world
Rechargeable batteries — a lithium-ion cell works by shuttling naked Li⁺ ions between electrodes. Also a first-line treatment for bipolar disorder, by a mechanism still not fully understood.
Table salt, glass, soap, and the yellow-orange street lamps that dominated cities for decades. Sodium ions carry every nerve impulse in your body.
Fertiliser above all — the "K" in NPK. Also essential to every cell you have; potassium-40 makes bananas and people faintly radioactive.
Atomic clocks. The second is defined by a caesium-133 transition, and rubidium clocks are compact enough to ride in GPS satellites.
None. It is so rare and so short-lived that no visible sample has ever existed.
Handling
All of them react with water and with skin moisture. Sodium and potassium can ignite spontaneously in humid air; potassium can form shock-sensitive peroxides on long storage. Alkali hydroxides — the products of those reactions — are strongly caustic and attack eyes fast.
Worth knowing
Common questions
Because they react with both the oxygen and the water vapour in air. Mineral oil excludes both. Lithium is stored in petroleum jelly instead, since it is light enough to float on most oils. Caesium and rubidium are usually sealed in glass ampoules under argon.
Francium, in principle — but it has never been made in a quantity you could react with anything. Among the metals you can actually obtain, caesium is the most reactive; it ignites on contact with air and reacts explosively with water even at −116 °C.
Hydrogen has one outer electron, which puts it at the top of group 1 by electron configuration. Chemically it behaves nothing like the alkali metals — it is a nonmetal gas that more often shares its electron than gives it away. Many periodic tables float hydrogen above the table entirely to acknowledge that it fits nowhere.
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