Definition · Plain-language
Alkali metals
The alkali metals are the soft, highly reactive metals in Group 1 of the periodic table, each with a single electron in its outer shell.
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The reactive metals of Group 1
The alkali metals form the first column of the periodic table, Group 1: lithium, sodium, potassium, rubidium, caesium and the rare, radioactive francium. They are unusual metals — soft enough to cut with a knife, shiny when freshly cut but quickly tarnishing, and much less dense than typical metals, with lithium, sodium and potassium light enough to float on water. Their name comes from the strongly alkaline (basic) solutions they form when they react with water, producing hydroxides.
One outer electron drives the chemistry
Every alkali metal has just a single electron in its outermost shell. This lone electron is held loosely and is easily lost, leaving a stable, positively charged ion with the electron arrangement of a noble gas. That readiness to give up one electron is what makes the group so reactive and explains why they always form ions with a single positive charge. Reactivity increases down the group: the outer electron sits further from the nucleus in the heavier metals, so it is lost more easily, making caesium far more reactive than lithium.
Reactions, storage and uses
Alkali metals react vigorously with water, producing hydrogen gas and an alkaline hydroxide, with the reaction growing more violent down the group — sodium fizzes and skates across the surface, while potassium ignites. They also react quickly with oxygen in the air, so they are stored under oil to keep moisture and air away. Despite their hazards, their compounds are everywhere: sodium chloride is table salt, lithium is used in rechargeable batteries, and potassium compounds are vital plant nutrients in fertilisers.
Key facts
At a glance
- Definition: the reactive metals of Group 1 of the periodic table
- Members: lithium, sodium, potassium, rubidium, caesium, francium
- Outer electrons: one, which is easily lost
- Ion formed: a single positive charge (e.g. Na⁺)
- Reactivity: increases down the group
- Stored: under oil, to keep out air and water
Common misconceptions
What people often get wrong
Often heard: Hydrogen is an alkali metal because it sits at the top of Group 1.
Actually: Hydrogen is placed in Group 1 for its single outer electron, but it is a non-metal with very different properties. The alkali metals proper begin with lithium.
Often heard: All metals react with water as dramatically as the alkali metals.
Actually: Most metals react with water slowly or not at all. The alkali metals are exceptional precisely because their single loose electron makes them so reactive, which is why they need special storage.
Often heard: Lithium is the most reactive alkali metal because it is the smallest.
Actually: Reactivity increases down the group, so caesium is far more reactive than lithium. The outer electron is further from the nucleus in heavier members and is lost more easily.
Going deeper
