Science, Maths & Technology
  • Video
  • 5 mins
  • Level 1: Introductory

Alkali metals

Updated Wednesday 25th July 2007

Discover the explosive results when water and alkali metals come together - and the science behind the reaction


Copyright The Open University

Text version

Now let's see another reaction of the alkali metals, the reaction with water.

We'll start with Lithium. The metal floats on the water and reacts with it, giving off Hydrogen gas.

Now for Sodium, the same sort of thing happens, although the reaction is a bit more vigorous. All the alkali metals react with water in the same way.

Now for Potassium. This time you'll see a flame. The heat given out by the reaction is produced so quickly that the Hydrogen gas catches fire, it burns with a lilac flame.

The next element is Rubidium. This time we've put a safety screen between us and the reaction.You can see that things gradually become more terrifying as we go down the group.

Let's try Caesium, our 5th alkali metal.
[Huge explosion]

The science

The alkali metals are the elements Lithium, Sodium, Potassium, Rubidium, Caesium and Francium. They are grouped together because they all behave similarly (except with different ferocity) and together form Group 1 of the Periodic Table.

They are in fact very soft metals that can be cut with a knife and have relatively low melting temperatures. They do not occur naturally because they react readily with air and moisture and so need to be stored under oil.

One of the signature reactions of alkali metals is their reaction with water to form alkaline solutions, for example sodium reacts with water to form sodium hydroxide – caustic soda.

The reaction of alkali metals with water is pretty vigorous and as we see in the video clip as we go down Group 1 of the Periodic Table, from Lithium to Caesium, things get more and more frightening.

Lithium is used to make rechargeable batteries and lightweight alloys. Some of its compounds are used as mood stabilising drugs.

Sodium (vapour) is used in bright yellow street lights. It is also used as a heat transfer agent in some types of nuclear reactor. Sodium salts are essential to life – ordinary table salt is sodium chloride.

Potassium salts are used as fertilisers, such as potassium chloride - which used to be called chloride of potash. Potassium nitrate is one of the components of gunpowder. Potassium salts are also essential to life.

Rubidium and Caesium have a number of specialist uses such as the use of Caesium in atomic clocks that are very accurate; and Rubidium, used in specialist glasses. Francium is an extremely rare metal mainly because it readily undergoes radioactive decay, with a half life of less than 22 minutes.


For further information, take a look at our frequently asked questions which may give you the support you need.

Have a question?

Other content you may like

Elements of the Periodic Table Creative commons image Icon The Open University under Creative Commons BY-NC-SA 4.0 license activity icon

Science, Maths & Technology 

Elements of the Periodic Table

Explore the impact of chemical elements on our bodies, our world, and see how they changed the course of history

Fizzy drinks Copyrighted image Icon Copyright: BBC article icon

Science, Maths & Technology 

Fizzy drinks

Find out what's really in those bubbles that give your drinks their fizz.

Hat makers, Greek gods and the great poisoners Copyrighted image Icon Copyright: © Ventin | - Shiny Mercury Photo article icon

Science, Maths & Technology 

Hat makers, Greek gods and the great poisoners

Ever wondered where the phrase 'as mad as a hatter' came from? We take a look at some infamous cases of poisoning. 

Iron transport and storage Copyrighted image Icon Copyright: Used with permission free course icon Level 3 icon

Science, Maths & Technology 

Iron transport and storage

This free course, Iron transport and storage, looks at the methods that have been developed by organisms for the uptake, transport and storage of iron: a process made more complicated by the insolubility of its oxides and hydroxides. You will examine iron storage in mammals, including humans,. This is achieved by ferritin which stores iron as a hydrated iron (III) oxide an example of biomineralisation.

Free course
5 hrs
article icon

Science, Maths & Technology 

Fireworks Challenge Glossary

Some of the key terms associated with making fireworks

Kitchen lab: Why does custard get lumpy, and why bother cooking at all? Copyrighted image Icon Copyright: Production team article icon

Science, Maths & Technology 

Kitchen lab: Why does custard get lumpy, and why bother cooking at all?

What is it that makes custard go lumpy? Can you make your own baking powder? Is your kitchen really a disguised lab?

Fruits of the vine Copyrighted image Icon Copyright: Yurok Aleksandrovich via audio icon

Science, Maths & Technology 

Fruits of the vine

An investigation into the chemistry of wine making from The New Curiosity Shop.

20 mins
DIY: Electrolysis Copyrighted image Icon Copyright: OU article icon

Science, Maths & Technology 

DIY: Electrolysis

A step-by-step guide to electrolysing water, part of the BBC/OU's programme website for Rough Science 1

Carbon process: Volcanism Copyrighted image Icon Copyright: article icon

Science, Maths & Technology 

Carbon process: Volcanism

One of the most poweful forces on the planet - no wonder volcanoes can move carbon around.