Group 1: The Alkali Metals

Group 1 is the first column of the periodic table and holds the alkali metals: lithium, sodium and potassium, followed by rubidium, caesium and francium. They are soft metals that can be cut with a knife, and freshly cut surfaces are shiny before they quickly tarnish in air.

Every alkali metal atom has exactly one electron in its outer shell. This shared feature is the reason the group members react in the same way. To reach a stable, full outer shell, each atom loses that single outer electron, forming a positive ion with a 1+ charge (for example Na⁺).

All Group 1 metals have one outer electron, which they lose to form a 1+ ion. Losing the same number of electrons is why they share their chemical reactions.

The group is called the "alkali" metals because their hydroxides dissolve in water to form alkaline solutions.

Alkali metals react readily with oxygen in the air, which is why they tarnish so fast and are stored under oil to keep air away.

The reaction forms a metal oxide. Each metal combines with oxygen in the same ratio, giving a general pattern across the group:

$4\text{Li}+{\text{O}}_2\to 2{\text{Li}}_2\text{O}$

$4\text{Na}+{\text{O}}_2\to 2{\text{Na}}_2\text{O}$

$4\text{K}+{\text{O}}_2\to 2{\text{K}}_2\text{O}$

The metal oxides formed are white solids. Because each metal forms a 1+ ion and oxygen forms a 2− ion, the formula of the oxide is always of the form M₂O, with two metal atoms to each oxygen atom.

Metal	Oxide formed	Formula
Lithium	Lithium oxide	Li₂O
Sodium	Sodium oxide	Na₂O
Potassium	Potassium oxide	K₂O

Alkali metals react with chlorine gas, burning vigorously to form a metal chloride, which is a white crystalline salt.

Each metal combines with chlorine in a 1:1 ratio of atoms because the metal forms a 1+ ion and chlorine forms a 1− ion:

$2\text{Li}+{\text{Cl}}_2\to 2\text{LiCl}$

$2\text{Na}+{\text{Cl}}_2\to 2\text{NaCl}$

$2\text{K}+{\text{Cl}}_2\to 2\text{KCl}$

Sodium chloride (NaCl) is ordinary table salt. All three chlorides are white ionic solids that dissolve in water. As with the other reactions, the more reactive the metal, the more vigorous the reaction with chlorine.

Metal	Chloride formed	Formula
Lithium	Lithium chloride	LiCl
Sodium	Sodium chloride	NaCl
Potassium	Potassium chloride	KCl

The reaction with water is the most memorable and the one exams ask about most. An alkali metal reacts with water to produce a metal hydroxide and hydrogen gas.

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

The metal floats and moves across the surface (it is less dense than water), fizzing as hydrogen is released. The heat produced can ignite the hydrogen. The metal hydroxide dissolves, making the solution alkaline, so universal indicator added to the water turns purple.

The three metals differ sharply in how violently they react:

Metal	What you see with water
Lithium	Fizzes steadily, moves slowly on the surface
Sodium	Melts into a ball, whizzes about, may ignite with an orange flame
Potassium	Reacts violently, ignites immediately with a lilac flame, may spark

Group 1 + water → metal hydroxide + hydrogen. Learn the general pattern; it lets you write the equation for any alkali metal.

Comparing lithium, sodium and potassium shows a clear trend: reactivity increases down Group 1. Potassium reacts far more violently than sodium, and sodium more vigorously than lithium.

Reacting means losing the single outer electron. The easier that electron is to lose, the more reactive the metal. Going down the group:

• the outer electron sits in a shell further from the nucleus;
• there are more inner shells between the nucleus and the outer electron, which shield it from the nuclear charge.

Both effects weaken the attraction between the nucleus and the outer electron, so it is lost more easily. That is why potassium (outer electron in shell 4) loses its electron more readily than sodium (shell 3) or lithium (shell 2).

Reactivity increases down Group 1 because the outer electron is further from the nucleus and more shielded, so the atom loses it more easily.

This trend lets you predict that rubidium and caesium, lower still, react even more violently than potassium.

1. Getting the reactivity trend backwards

Reactivity increases down Group 1. Lithium is the least reactive of the first three and potassium the most reactive. This is the opposite of Group 7.

2. Explaining the trend with "atoms get bigger" alone

The mark-scheme explanation is that the outer electron is further from the nucleus and shielded by more inner shells, so it is held less strongly and lost more easily. "Bigger atoms" on its own does not explain why the electron is lost more readily.

3. Forgetting hydrogen in the water reaction

The products of Group 1 + water are a metal hydroxide and hydrogen gas. Missing out the hydrogen, or writing a metal oxide instead of a hydroxide, loses marks.

4. Writing the wrong ion charge

Group 1 metals form 1+ ions by losing one electron. Do not write Na²⁺ or give oxides a formula like NaO; the correct oxide is Na₂O.

5. Saying the solution turns acidic

The metal hydroxide makes the solution alkaline, turning universal indicator purple. It does not turn acidic or red.

6. Unbalanced oxygen equations

The reaction with oxygen needs four metal atoms per O₂ molecule, for example 4Na + O₂ → 2Na₂O. Check the oxygen atoms balance (two on each side) before moving on.