Where are the alkali metals?

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Where are the alkali metals?

The elements in group 1, on the left of the periodic table, are called the alkali metals.

These metals are all very reactive and are rarely found in nature in their elemental form.

lithium

sodium

potassium

rubidium

caesium

francium Fr

Cs

Rb

K

Na

Li


What are the alkali metals?


Why are they called the ‘alkali metals’?

The alkali metals are so reactive that, as elements, they have to be stored in oil. This stops them reacting with oxygen in the air.

The alkali metals are unlike most other metals, which are usually hard and dense.

The elements in group 1 also react with water and form alkaline compounds. This is why they are called alkali metals.

Alkali metals are soft enough to be cut with a knife, and the most common alkali metals, lithium, sodium and potassium, all float on water.


What is the electron structure of alkali metals?

The alkali metals all have one electron in their outer shell.

lithium2,1

sodium2,8,1

potassium2,8,8,1

They are found in group 1 of the periodic table.

They have similar physical and chemical properties.

This means that:

They can readily lose the outer shell electron to form positive ions with a +1 charge and a full outer shell.


How do you identify alkali metals?



What are the properties of the alkali metals?

The characteristic properties of the alkali metals are:

They are shiny. This is only seen when alkali metals are freshly cut.

They are good conductors of heat and electricity.

They are soft and can be cut by a knife. Softness increases going down the group.

They have a low density.Lithium, sodium and potassium float on water.

They have low melting and boiling points.

These properties mean that the alkali metals are different to typical metals. However, alkali metals do also share some properties with typical metals:


What is the trend in density?

The alkali metals generally become more dense going down the group, but the trend is not perfect because potassium is less dense than sodium.

Water has a density of 1 g/dm3.

Element Density (g/dm3)

lithium

potassium

sodium

rubidium

caesium

0.53

0.97

0.86

1.53

1.87

Which elements in group 1 will float on water?


What are the trends in density?


What is the trend in melting and boiling point?

The melting points and boiling points of alkali metals decrease going down the group.

Element Melting point (°C)

lithium

potassium

sodium

rubidium

caesium

181

98

64

39

28

Boiling point (°C)

The melting and boiling points decrease going down group 1 because the atoms get larger. In each metallic structure, the attraction between the positive metal ions and the delocalized sea of electrons gets weaker and so they become easier tomelt, and to boil.

1342

883

760

686

671


What are the trends in melting point?


What are the trends in boiling point?


Properties of alkali metals quiz



How do the alkali metals react with oxygen?

All alkali metals react with oxygen in the air to form metal oxides. This produces a layer of dull oxide on the surface of the metal, called tarnish.

The speed with which alkali metals react with oxygen in the air increases going down the group:

Why are alkali metals stored in oil?

lithium – tarnishes slowly

sodium – tarnishes quickly potassium – tarnishes very quickly.

The oil prevents them from reacting with oxygen and tarnishing.


What are the word and chemical equations for the reaction that causes sodium to tarnish?

What is the equation for the reaction with oxygen?

The reaction between an alkali metal and oxygen is an example of an oxidation reaction:

alkali metal + oxygen alkali metal oxide

4Na (s) + O2 (g) 2Na2O (s)

sodium + oxygen sodium oxide

The word and chemical equations for the reaction between lithium and oxygen are:

4Li (s) + O2 (g) 2Li2O (s)

lithium + oxygen lithium oxide


How do the alkali metals react with water?


All the alkali metals react vigorously with water.

The reaction produces a gas that ignites a lighted splint with a squeaky pop. What is this gas?

What does the reaction with water produce?

It is an exothermic reaction as it releases a lot of heat.

When green universal indicator is added to the reaction mixture, it turns purple. What does this tell you about the products of this reaction?

The reaction with water becomes more vigorous as you go down the group.


2M(s) + 2H2O(l) 2MOH (aq) + H2(g)

alkali metal + water alkali metal + hydrogen hydroxide

This reaction creates alkaline hydroxide ions.

The general equation for the reaction between an alkali metal reacting with water is:

What is the equation for the reaction with water?

This is why the group 1 elements are called the alkali metals.


How does lithium react with water?

Lithium is the least reactive of the alkali metals.

2Li (s) + 2H2O (l) 2LiOH (aq) + H2 (g)

lithium + water lithium + hydrogen

hydroxide

When added to water, it fizzes and moves around slowly across the surface of the water.

What is the equation for this reaction?


How does sodium react with water?

When added to water, sodium fizzes more than lithium, and moves quickly across the surface of the water.

2Na (s) + 2H2O (l) 2NaOH (aq) + H2 (g)

sodium + water sodium + hydrogen hydroxide


The hydrogen sometimes catches fire because of the heat from the reaction.

The sodium melts as it reacts, and it becomes spherical and shiny, like a ball bearing.


How does potassium react with water?

When added to water, the potassium moves across the surface of the water very quickly.

2K (s) + 2H2O (l) 2KOH (aq) + H2 (g)

potassium + water potassium + hydrogen hydroxide


Like sodium, it melts with the heat of the reaction.

The reaction produces so much heat that the hydrogen given off catches alight. What colour would the flame be?


How do alkali metals react with water?

Which of the alkali metals will react most strongly with water?


How does electron structure affect reactivity?

The reactivity of alkali metals increases going down the group. What is the reason for this?

The atoms of each element get larger going down the group.

This means that the outer shell electron gets further away from the nucleus and is shielded by more electron shells.

The further an electron is from the positive nucleus, the easier it can be lost in reactions.

This is why the reactivity of the alkali metals increases going down group 1.

incr

ease

in

rea

ctiv

ity

K

Li

Na


What is the order of reactivity?


Alkali metals burst into flames when heated and added to chlorine. They form metal chlorides.

How do alkali metals react with chlorine?

2Li (s) + Cl2 (g) 2LiCl (s)

lithium + chlorine lithium chloride

What are the word and chemical equations for the reaction that produces sodium chloride?

2Na (s) + Cl2 (g) 2NaCl (s)

sodium + chlorine sodium chloride

alkali metal + chlorine alkali metal chloride

The word and chemical equations for the reaction between lithium and chlorine are:


True or false?



What are the uses of alkali metals?

How many uses of alkali metals can you see below?







Glossary

alkali metal – An element that belongs to group 1 of the periodic table.

exothermic – A reaction that releases heat into its surroundings.

metal chloride – The type of solid produced when an alkali metal is burned in chlorine gas.

metal hydroxide – The type of alkali produced by the reaction between an alkali metal and water.

metal oxide – The type of solid produced when an alkali metal reacts with oxygen.

oxidation – The process by which a substance reacts and combines with oxygen.

tarnish – The discolouration of metal after exposure to air caused by the formation of an oxide on the metal’s surface.


Anagrams


Completing alkali metal equations


Comparing reactivity with water


Multiple-choice quiz

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Where are the alkali metals?