METALS
A metal is an element which has the ability to lose electron(s) and became positively charged. There are about 105 different
elements. Of these 84 are metals and 21 are non metals.
GENERAL PROPERTIES
Metals generally have the following properties.
i.
ii.
iii.
iv.
v.
vi.
vii.
viii.
ix.
x.
xi.
Have high melting and boiling points
Are good conductors of heat and electricity
Have a high density – metal atoms are parked very closely
Are solids at rtp, except for mercury which is a liquid.
Are Malleable i.e can be beaten into sheets
Are Ductile i.e can be made into wires.
Are Sonorous i.e produce sound when beaten
Are Lustrous i.e can be polished or have a shining surface.
They are strong under tension and compression. That means they can withstand stretching and crushing without
breaking
React with oxygen to form basic oxides
Form positively charged ions (Cations) by losing electrons.
WHY METALS ARE USED AS ALLOYS
Pure metals are usually too soft and weak for most uses. A gold chain is never made of pure gold, as the chain would be too
soft and would break easily. Instead, it is alloyed with other elements to make it more shiny and stronger.
Metals are mainly used as alloys for the following reasons
 To improve on their properties.
 To improve on their appearance.
 To make metals to be less brittle.
 To Make metals strong and harder.
A comparison between pure metals and alloys is shown below.
Pure metal
Alloy
Are usually Soft and can easily bent
Are Strong and hard, not easily bent
Have higher melting points
Have lower melting points than the melting
points of their components
Atoms can slide over each other easily as atoms are of
the same size
Diagramatic representaion of a pure metal
Atoms cannot slide over each other easily as
foreign atoms are of different size and disrupt
the orderly arrangement of the metal atoms
Diagrammatic representation of an alloy
METAL ALLOYS
An alloy is a mixture of a metal with another element. Alloys mainly consist of two or more metals mixed together or they may
be largely a metal with a non-metal. An alloy is usually made by melting the main metal and then dissolving the other
substances in it.
Alloys have certain properties that differ from those of their components and make them more suitable for particular purposes
than their parent metals.
There are thousands of different alloys; here are the examples of common ones;
Alloy
Composition
Special Properties
Aluminium alloys
Duralumin
Uses
Aluminium, copper and
magnesium
Aluminium, cobalt and
and nickel
harder and corrosive
resistance
Retains magnetism
Aircraft bodies
Copper alloys
Brass
Copper and zinc
Sonorous, Stronger, highly
ductile and malleable
Bronze
Copper and tin
Monel
Copper, nickel and
manganese
Corrosion resistance and
harder
Corrosion resistance
Make musical instrument, pins of
electrical plugs, Deep drawn materials
,hot rolled materials
Money coin, trophies,
Alnico
Iron alloys
Mild steel
Permanent magnets
Chemical plant
Iron(95.5%) and
carbon(o.5%)
Iron(99%) and
carbon(1%)
Iron(84%) ,silicon(15%)
and carbon(1%)
harder and strong
High speed steel
Iron and tungsten
Heat resistance, very hard
Stainless steel
Iron,chromium and
nickel
Corrosion resistance, very
hard
Hadfields steel
Iron and manganese
Abrasion resistant
Lead alloys
Common solder
Lead and tin
Wide liquid range and sharp
low melting point
Metal joints (joining wires and pipes)
Lead, Tin, Bithmuth,
and mercury
Hardens quickly, abrasion
resistant
Filling dental cavities
Hard steel
Duriron
Dental amalgam
Very hard, stronger
Acid resistance, corrosion
resistance, hard
Construction works, machinery tubings,
window grills, car bodies
Blades for cutting tools (e.g razor blades/
saws) sand paper, drill bits
Tanks and pipes for chemical plants,
industrial equipment that comes into
contact with corrosive chemicals
Making high speed cutting tools, ball
bearing and drill bits
Making of cutlery e.g knives), surgical
instruments, kitchen sink, chemical
plants and cutting tools
Heavy drill bits, rock crusher jaws,
railway points
REACTIVITY SERIES OF METALS
This is the arrangement of elements in order of their chemical reactivity. The numbers of different reactions have been used to
compare the reactions of the elements.
To come up with the reactivity series, chemists compared the reactions of different metals with;
i.
Air (oxygen)
ii.
Cold water
iii.
Steam
iv.
Dilute acids etc
In the reactivity series the most reactive metals are placed on top while the least reactive at the bottom, as shown
Potassium
K
Sodium
Na
Calcium
Ca
Magnesium
Mg
Aluminium
Al
Zinc
Zn
Iron
Fe
(Hydrogen)
H
Copper
Cu
Silver
Ag
Gold
Most reactive
Decreasing reactivity
*
Au
Least reactive
* Hydrogen although is not a metal has been included in the series to act as a reference point to indicate its position
Any metal higher than hydrogen in the series will displace hydrogen from an acid where as those below it will not.
USEFUL INFORMATION TO REMEMBER ABOUT THE REACTIVITY SERIES
1.
The metal at the top of the series generally, react more vigorously than those that are at below the series
2.
The more reactive the metal is, the more compounds it forms so only metals below the series e.g. gold, silver platinum are found as
elements in the earth’s crust. The other reactive metals are found as compounds.
3.
When a metal reacts, it gives up electrons to form ions. The more reactive the metal, the more easily it gives up electrons.
4.
The more reactive the metal, the more stable its compounds. Stable means difficult to break down. Compounds of metals high in
the reactivity series are difficult to split because they form strong bonds (stable compounds)
5.
All metals in the reactivity series undergo displacement reactions. Metals higher in the reactivity series will displace from aqueous
solution of its salt any metal below it. The greater the gaps separating the metal the more easily does the displacement take place.
6.
The more reactive the metal , the more it is difficult to extract from its compounds since the compounds are stable. Hence, for
more reactive metals , you need a tough method of extraction; Electrolysis.
7.
If you place two metals in an electrolyte and join them up, you’ll get the current! Electrons flow from a more reactive metal to a
least reactive one. In an electrolytic cell, The further apart the metals are in the reactivity series , the higher the voltage of the cell.
REACTIONS RELATED TO THE REACTIVITY SERIES
Knowing the position of the reactivity series will help us determine the type of chemical reaction that may occur and the rate of
such a chemical reaction.
The following are the reactions;
A. DISPLACEMENT REACTIONS OF METALS.
i.
Displacement of a one metal by another in aqueous solution.
Metals high in the reactivity series will displace the least reactive metals in solution.
e.g
Zn (s) + CuSO4 (aq)
ZnSO4 (s) + Cu (s)
BUT, a less reactive metal cannot displace a more reactive metal from its solution
e.g
Fe (s) + CaCO3 (aq)
Fe (s) + CaCO3 (aq) ; No reaction takes place
(NO reaction takes place, Fe cannot displace Ca from its solution)
ii.
Reduction of metal oxides by a more reactive metal.
A metal high in the reactivity series has a high affinity for oxygen .hence, a more reactive metal will remove
oxygen from the a less reactive metal and bond with the oxygen instead.
e.g
Fe (s)
+ CuO (aq)
FeO (s) + Cu (s)
iii.
Reduction of metal oxides by carbon.
At high temperature, carbon behaves as a reducing agent and reduces metal oxides to metals, removing the
oxygen from the metal oxides.
e.g
C (s)
+ 2 PbO (s)
CO2 (s) + 2 Pb (s)
NB
 Carbon cannot reduce oxides of reactive metals like potassium, calcium, magnesium and aluminium.
 Carbon reduces oxides of metals lower in the reactivity series i.e Zinc and those metals below.
iv.
Reaction of metal oxides with hydrogen
Hydrogen is also a good reducing agent, it can reduce metal oxides to metals. BUT hydrogen can only reduce
oxides below zinc in the reactivity series.
e.g
H2 (g)
+ CuO (aq)
H2O (l) + Cu (s)
v.
Reaction of metals with acids
Metals above hydrogen in the reactivity series will displace hydrogen from acids forming a salt and hydrogen gas.
e.g
Zn (s) + H2SO4 (aq)
ZnSO4 (aq)
+ H2 (g)
2 Mg (s) + HNO3 (aq)
Mg(NO3)2 (aq) + H2 (g)
Cu (s)
+
HCl (aq)
(Cu cannot displace H from its solution)
Cu (s) + HCl (aq)
; NO reaction takes place
B. REACTION OF METALS WITH OXYGEN.
Metals react with oxygen to form metal oxides
i.
Potassium, sodium and calcium react with oxygen in the air to form metal oxide
e.g
4Na (s) +
O2 (g)
2Na2O (s)
ii.
Magnesium, Aluminium, Zinc and Iron burns when heated to form a metal oxide.
e.g
2Mg (s) +
O2 (g)
2MgO (s)
iii.
Tin, lead, copper and mercury form metal oxides slowly on heating.
e.g
2Cu (s) +
O2 (g)
2CuO (s)
NB; Silver and Gold do not react with oxide.
C. REACTION OF METALS WITH DILUTE HYDROCHLORIC ACID
Metals above hydrogen in the reactivity series react with acids to form a salt and hydrogen gas.
e.g
K (s) +
HCl (aq)
KCl (aq)
+ H2 (g)
React explosively
Ca (s) + 2 HCl (aq)
CaCl2 (aq) + H2 (g)
React vigorously
Mg (s) + 2 HCl (aq)
MgCl2 (aq) + H2 (g)
React rapidly in warm acids
2Al (s) +
6 HCl (aq)
2 AlCl3 (aq) + H2 (g)
React slowly; warming may be required.
Cu (s) +
HCl (aq)
Cu (s) +
HCl
NO Reaction takes place
NB; The more reactive the metal , the more vigorously the reaction
D. REACTION OF METAL WITH WATER
i.
Potassium, Sodium and calcium react readily with cold water. The products are metal hydroxide and hydrogen
gas.
e.g
2Ca (s) + 2H2O (l)
2Ca(OH)2 (aq)
E.
ii.
Magnesium, aluminium, zinc ,and iron do not react with cold water but react with steam to producemetal oxides
and hydrogen gas.
e.g
2Mg (s) + 2H2O (g)
2Mg(OH)2 (s)
iii.
Metals below hydrogen do not react with cold water or stem.
ACTION OF HEAT ON METAL CARBONATES
i.
Potassium and sodium carbonates cannot be decomposed be heating.
e.g
heat
Na2CO3 (s)
Na2CO3 (s)
NO Decomposition
ii.
Metals below sodium form carbonates that can be decomposed by heating.
e.g
heat
CaCO3 (s)
CaO (s) + CO3(g)
EXTRACTION OF METALS
Metals high in the reactivity series do not exist in their free state, but combined withother elements to form metal ores or
salts. Metal ores are usually in the form of oxides, sulphides or carbonates.
The extraction of metals depends on their reactivity. There are two basic methods of extraction of metals from their ores.
These are;
i.
Electrolysis and
ii.
Reduction.
The method used to extract the metal depends on the reactivity of the metal. Metals high in the reactivity series are extracted
by electrolysis. These metals include potassium, sodium, calcium, magnesium and aluminium. The moderately reactive metals
are extracted by the Reduction process. These include iron, copper, lead, tin and zinc. The unreactive metals are are found as
pure and uncombined elements as their ores occur naturally.
RUSTING OF IRON
When a metal is attacked by air, water or other substances in its surroundings the metal is said to corrode. Corrosion of iron
and steel is called RUSTING.
Rusting occurs when iron comes into contact with water and oxygen. Rust is actuall hydrated iro(ii) oxide, Fe2O3.H2O.
CONDTION FOR RUSTING
The diagrams below show conditions for rusting.
HOW TO PREVENT RUSTING
To prevent iron from rusting water and/or air(oxygen) must be prevented from coming into contact with the metal surface.
Below are some of the methods; They mostly involve coating the metal with something to keep out air and water.
1.
2.
3.
4.
5.
6.
PAINTING: Paints that contain lead or zinc are mostly used
OILING ( or greasing): this prevents air(oygen) from coming into contact with the metal surface
GALVANIZING: Coating the iron with a zinc metal.
SACRIFICIAL PROTECTION: Coating the metal with a more reactive metal e.g magnesium
ELECTROPLATING: Coating the iron with a less reactive metal. It is deposited on the iron by electrolysis process.
e.g
Tin plating and chromium plating
ALLOYING: When iron is made into stainless steel or chromium steel it does not rust.