Many metals will react with oxygen to produce metal oxides:
metal(s) + oxygen(g) → metal oxide(s)
No doubt at some time in your science lessons you will have held a piece of magnesium ribbon in a Bunsen flame and
cautiously observed the bright flash from the burning magnesium. However not all metal oxygen reactions are
as violent this.
Burning copper metal
If a square of coppermetal is held with a pair of tongs in a
hot Bunsen flame for about 30 seconds then the shiny
bronze coloured copper metal turns black; this is shown in the image opposite. No flames or bright flashes are produced. It may not seem like it but the copper metal
is reacting in a similar way to the burning magnesium ribbon,
it is reacting with the oxygen in the air; that is the copper metal is being oxidised. An equation for this oxidation reaction is:
copper(s) + oxygen(g) → copper oxide(s)
In both the examples above the metals join with oxygen from the air and turn into a metal oxide.
The metal is oxidised in these reactions. Oxidation simply means adding oxygen to a substance.
The reactivity series
potassium
sodium
lithium
calcium
magnesium
aluminium
carbon
zinc
iron
tin
lead
hydrogen
copper
silver
gold
platinum
By observing how violent and fast the reactions of metals are; for example when they are burned, when they react with water or react with
acids it is possible to rank the metals in order of reactivity.
The reactivity series is simply a list with the most reactive
metal at the top and the least reactive metal at the bottom. An outline of the reactivity series showing some of the common metals and two non-metals (carbon and hydrogen) in the periodic table is shown opposite.
Reaction of metals with water- oxidation and reduction
A common reaction you will have no doubt have met is the reaction of metals with water. Reactive metals, that is those close to the top of the reactivity series will react with water to produce a metal hydroxide solution, that is an alkaline solution and release hydrogen gas; we can show this as:
metal(s) + water(l) → metal hydroxide(aq) + hydrogen(g)
For example the image below shows what happens when the metals calcium, magnesium and copper are added to a test-tube of water.
Here:
Calcium reacts vigorously with water to form an alkaline solution of calcium hydroxide and lots of bubbles of hydrogen gas are seen an equation for this reaction is:
Magnesium reacts were slowly with water. This is perhaps a surprising result since magnesium is generally considered a reactive metal. Magnesium reacts slowly with water because as it starts to react with water its surface quickly becomes coated with a thin, insoluble layer of magnesium hydroxide; Mg(OH)2, being insoluble this layer will act as a barrier preventing further water from coming into contact with the underlying magnesium metal and slowing down the reaction. As a result, only a small amount of hydrogen gas is produced when magnesium is placed in cold water, and so the reaction is much slower compared to calcium or the violent reactions of water with the group 1 alkali metals such as lithium, sodium or potassium. The alkali metals react in a similar way with water as calcium and form an alkaline solution of the metal hydroxide and release hydrogen gas e.g. an equation for the reaction of the alkali metal lithium with water is shown as:
While the reaction of magnesium with water is very slow due to the formation of a layer of insoluble magnesium hydroxide on the surface of the magnesium metal; the reaction of magnesium with steam is very violent and exothermic. The heat produced in this reaction also prevents the formation of the protective layer which resulted in a very slow reaction between the magnesium and water.
If the bottom of a boiling tube is packed with wet heat resistant wool; as shown in the diagram below and a Bunsen flame is slowly moved back and forwards between coils of magnesium ribbon and this damp wool then after a short period of heating a brilliant white glow is seen as the magnesium reacts very violently with the steam produced by heating the wet wool.
The hydrogen gas produced in this reaction will "fly out" through the end of the boiling tube where it readily ignites and burns with a large pale blue flame.
The alkali metals and the metals radium, barium, strontium and calcium from group 2 of the periodic table
(the alkaline earth metals) all react
violently with water. However even a fairly reactive metal like magnesium reacts very slowly with water and it
would take days to collect enough hydrogen for a pop test! Remember the general trends in the reactivity of
metals; the
metals become more reactive as you descend a group in the periodic table. The reason for this is because the
metals lose their outer
electrons more readily as you descend the group and so their reactivity increases.
When the metals react with water or oxygen they are losing their valence or outer shell electrons to form positively charged ions called cations e.g.
Metal - e → metal+
In the case of lithium reacting with water we have:
Li(s) - e → Li+(aq)
The lithium hydroxide formed is an ionic compound with positively charged lithium ions and negatively charged hydroxide ions (OH-(aq)).
Metals when they react lose electrons to form positively charged ions. We defined
oxidation earlier as the addition
of oxygen to a substance however we can extend this definition to include the loss of one or more electrons.Non-metals unlike metals gain electrons from
metals when they react with them to form a negatively charged ion. The gain
of electrons is often called reduction e.g.
In the ionic equation, we can clearly see that the copper atoms lose 2 electrons to form copper ions with a
2+ charge while the oxygen atoms gain 2e and form oxide ions with a 2- charge. The copper
is oxidised and the
oxygen is reduced. Reactions where one substance is reduced and another is oxidised are called
redox reactions.
Self-check: The reactivity series
Part of the reactivity series is shown below; simply place the elements in the correct order, most reactive first. When you done press the check answer button.
Order the Reactivity Series (8 items — 1 = most reactive)
Metals (drag or tap to place)
Rank (1 = top)
Self-check: equations
Complete the following equations by simply clicking on the correct answer(s) and then on the boxes where they should go, disbale the "enforce correct order" button if you wish to place your choice in any order. Click the check answer button after every equation.
Complete the Word Equations
Question 1 of 5
Drag (or tap) the correct products into the blanks.
Key Points
Oxidation can be thought of as adding oxygen or removing electrons from a substance.
Metals are oxidised when they react with non-metals. This means they lose electrons and form positively charged ions.
Some metals will react with water to form alkaline solutions; that is a solution of a metal hydroxide. The gas hydrogen is also released.
Reduction is the gain of electrons or the removal of oxygen from a substance.
If a square of copper metal is held with a pair of tongs in a
hot Bunsen flame for about 30 seconds then the shiny
bronze coloured copper metal turns black; this is shown in the image opposite. No flames or bright flashes are produced. It may not seem like it but the copper metal
is reacting in a similar way to the burning magnesium ribbon,
it is reacting with the oxygen in the air; that is the copper metal is being oxidised. An equation for this oxidation reaction is:
