How do Group 1 metals react with water?

They form a metal hydroxide and hydrogen gas, and the hydroxide makes an alkaline solution. Sodium and water: 2Na(s) + 2H2O(l) - 2NaOH(aq) + H2(g). The hydroxide dissolves to give an alkaline solution, which is why the group is called the alkali metals.

Group 1 Notes

Oxford AQA IGCSE Chemistry: Revision notes

Key facts

Group 1 is the alkali metals: lithium, sodium, potassium and others below.
They are soft, shiny when cut, with low density (the first three float on water).
They lose one outer electron to form $1+$ ions and make white ionic compounds that dissolve to give colourless solutions.
They react with water to make a metal hydroxide (an alkali) and hydrogen.
Reactivity increases down the group.

Group 1 is the first column: the alkali metals.

Properties

Group 1 metals are soft, shiny when freshly cut, and have low density and low melting points for metals.

The first three (lithium, sodium and potassium) are less dense than water and float on it. They are soft enough to cut with a knife but tarnish quickly in air. Melting points decrease down the group.

Melting points of the Group 1 metals decrease down the group.

Which three Group 1 metals float on water?

With non-metals

They lose one outer electron to form ionic compounds containing 1+ ions.

A Group 1 atom has one outer electron. It loses it to form an ion with a single positive charge. The ionic compounds are usually white solids that dissolve to give colourless solutions. For example sodium and chlorine make sodium chloride, $\ce{NaCl}$ .

Sodium atom

2,8,1

Sodium ion

2,8

A sodium atom loses its one outer electron to become a Na⁺ ion with a full outer shell.

Group 1 atomloses 1 outer electron $\to$ ion with a $1+$ charge

What charge do Group 1 ions carry?

With water

They form a metal hydroxide and hydrogen gas, and the hydroxide makes an alkaline solution.

Sodium and water: $\ce{2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g)}$ . The hydroxide dissolves to give an alkaline solution, which is why the group is called the alkali metals.

1
Sodium added to water
2Na + 2H₂O
2
Hydrogen gas given off
the metal fizzes
3
Sodium hydroxide forms
NaOH dissolves to give an alkaline solution

Sodium reacting with water.

Metal + water $\to$ metal hydroxide + hydrogen

Which gas is released when a Group 1 metal reacts with water?

Reactivity trend

Reactivity increases down the group because the outer electron is lost more easily.

Going down, the outer electron is in a shell further from the nucleus, so it is held less strongly and is lost more easily. Potassium reacts more vigorously than sodium, which is more vigorous than lithium.

Lithium

2,1

Sodium

2,8,1

Potassium

2,8,8,1

Down Group 1 the outer electron is further from the nucleus, so it is lost more easily.

Which is more reactive, sodium or potassium?

Try an exam question

Describe what you would see when a small piece of potassium is added to water, and explain why potassium is more reactive than lithium.

[4 marks]

That's the notes covered.

Carry on to the next subtopic.