The Alkali Metals (Group 1)

The alkali metals are the highly reactive metals in Group 1 of the periodic table. They react vigorously with water and air, producing hydrogen gas and metal hydroxides. Their reactivity increases going down the group.

What Are the Alkali Metals?

The alkali metals are the elements in Group 1 of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).

They are called "alkali metals" because they react with water to form alkaline (basic) hydroxide solutions.

Despite being metals, they are soft enough to cut with a knife and have unusually low densities — lithium, sodium, and potassium all float on water.

Why Are They Reactive?

Each alkali metal has one electron in its outer shell. To get a full, stable outer shell it needs to lose this one electron. This makes alkali metals very eager to react — they readily lose that electron to form 1+ ions (e.g. Na⁺, K⁺).

Reactions with Water

Alkali metals react vigorously with cold water, producing:

$\text{metal} + \text{water} \rightarrow \text{metal hydroxide} + \text{hydrogen gas}$

Lithium: gentle fizzing, slides around on the surface
Sodium: fizzes vigorously, melts into a ball, moves quickly
Potassium: ignites the hydrogen with a lilac/violet flame, moves very fast

$2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2$

Warning

Alkali metals must be stored under oil to prevent them from reacting with air and moisture. Never touch them with bare hands. Caesium and francium react explosively with water.

Trend Down the Group

As you go down Group 1, reactivity increases because:

The outer electron is further from the nucleus
It is held less tightly (more shielding by inner electrons)
It is more easily lost in reactions

Element	Outer electrons	Reactivity
Lithium	2, 1	Least reactive
Sodium	2, 8, 1	Moderate
Potassium	2, 8, 8, 1	Very reactive
Rubidium	2, 8, 18, 8, 1	Extremely reactive

Physical Properties

All alkali metals:

Are shiny silver when freshly cut but tarnish quickly in air
Have low melting points (for metals)
Are excellent conductors of electricity and heat
Are lighter (less dense) than most metals

Real world: Sodium in your diet and body

Sodium ions (Na⁺) are essential in your body — they regulate nerve impulses, muscle contractions, and fluid balance. Table salt (NaCl) is your main dietary source of sodium. However, because sodium metal itself reacts violently with water, your body only uses it as the safe Na⁺ ion in solution, not as the dangerous metallic form.

Real world: Lithium in rechargeable batteries

Lithium is the lightest of the alkali metals and is used in lithium-ion batteries that power smartphones, laptops, and electric cars. Although lithium metal is reactive (it reacts with water), in batteries it operates in a controlled chemical environment. The low density and high reactivity (willingness to lose electrons) of lithium make it ideal for energy storage.

Real world: Potassium for plant fertilisers

Potassium (K) is one of the three main nutrients in agricultural fertilisers (the others being nitrogen and phosphorus — NPK fertilisers). Plants absorb potassium ions from soil to support growth, photosynthesis, and disease resistance. The K in "NPK" stands for Kalium, potassium's Latin name. This is why potash (potassium compounds) is mined and spread on fields worldwide.

Tip

Where do you see this in real life? Lithium in your phone battery, sodium in your food salt, potassium in fertiliser bags labelled "NPK". All are Group 1 alkali metals — highly reactive with water, stored under oil, and essential to modern life in their ionic (safe) forms.