Reactivity series

 

The pH scale

Reactivity of metals

There are about 95 metals in the periodic table. Metal elements are found on the left and in the middle of the periodic table. Non-metals are found on the right.

 

The periodic table of elements

Unreactive metals

Some metals do not react easily. They do not join in chemical reactions very often. For example, copper is not very reactive, so it is good for making water pipes. The water pipes will not react with the water that flows through them.

We can use unreactive metals as they are. For example, platinum is good for jewellery because it does not react with anything, so it always stays shiny.

 

Reactive metals

Some metals are very reactive. They join in chemical reactions very easily.

Lithium, for example, is a very reactive metal. It reacts so quickly that it has to be stored under oil. This stops it from touching the oxygen and moisture in the air. If it did touch the air, it would react very fast.

Lithium makes bubbles of gas when it is put in water. The gas is hydrogen.

Copper is a less reactive metal. It does not react with water at all. It just sinks to the bottom of the beaker.

We mainly use reactive metals in compounds. They have special uses. For example, calcium metal makes hydrogen gas when it reacts with water. But calcium carbonate is in many rocks that we use to build things and make roads.

 

Observing reactivity

We can use chemical reactions to see how reactive different metals are. Reactive metals will show changes that we can see, like gas bubbles or flames. Unreactive metals will not show any changes. There are three main types of chemical reactions that we can use to compare metal reactivity. These are reactions of metals with:

 

• water
• oxygen
• acids

 

1. Metals and water

Water reacts with some metals, but not with others. Hydrogen gas is made when water and a metal react. The gas can catch fire.
The image below shows three different metals reacting with water:

 

• Calcium (Ca)
• Lithium (Li)
• Potassium (K)

   

  

   

  The table below shows these metals in order of reactivity with water (from most reactive to least reactive):

   

  Reactivity	Metal	Reaction
  Most reactive	Potassium (K)	Sparks and a flame produced on contact with cold water
  ↑	Sodium (Na)	Lots of bubbles and movement with cold water
  Least reactive	Calcium (Ca)	Tiny bubbles produced slowly with cold water

 

 

2. Metals and oxygen

When a metal reacts with oxygen, it makes a metal oxide.

metal + oxygen → metal oxide

 

• Oxygen makes the most reactive metals burn brightly.
• Less reactive metals slowly change their colour.
• Oxygen does not react with the least reactive metals.

 

The table below shows various metals in order of their reactivity with oxygen:

 

Reactivity	Metal	Reaction
Most reactive	Caesium (Cs)	Reacts immediately with oxygen in the air.
↑	Magnesium (Mg)	Burns in air producing a white flame when heated by a Bunsen burner.
↑	Copper (Cu)	Slowly changes colour when heated by a Bunsen burner.
Least reactive	Gold (Au)	Does not react with oxygen.

 

3. Metals and acid

Acids have a pH lower than 7. They make similar observations as water when they react with metals.

Acids do not react with unreactive metals, but very reactive metals like potassium react very quickly and may even make flames.

 

 

The table below shows various metals in order of their reactivity with acid:

 

Reactivity	Metal	Observation
Most reactive	Potassium (K)	Sparks / flame produced when contacts with acid.
↑	Magnesium (Mg)	Lots of bubbles and movement on contact with acid.
↑	Zinc (Zn)	Tiny bubbles are produced slowly on contact with acid.
Least reactive	Platinum (Pt)	Does not react to acid.

 

Acids do not react with platinum, gold and copper. They are very unreactive metals. They are at the bottom of the reactivity series in the diagram. Lead, tin and zinc are more reactive. They make very small bubbles in a slow reaction with acids. They are above platinum, gold and copper in the diagram. Aluminium, magnesium and calcium react fast with dilute acids. They are above zinc, tin and lead in the diagram. Potassium and sodium react very violently with dilute acids. They make sparks and maybe a small explosion.

 

The reactivity series

We can use the reactions of metals with oxygen, water and acid to make a reactivity series of metals.

The metals that react very fast and violently are the most reactive.

The metals that do not show any change are the least reactive.

The reactivity series is a list of the metals in order of reactivity, from the most reactive at the top to the least reactive at the bottom.

See diagram below of the reactivity series of different metals and their reactions:

 

 

The reactivity series of different metals and their reactions with oxygen, water and acids.

 

Summary:

 

• Some metals are more reactive than others. They join in chemical reactions more easily.
• We can use what we see in the reactions to make a list of the metals based on their reactivity.