Metals – their properties, structure
and bonding
L.O:
To understand how the structure
of metals affect their properties
Electrons and metallic bonding
How is the sea of electrons involved in metallic bonding?
What is the structure of metals?
Metals are giant structures of atoms.
The atoms in a pure metal are in
tightly-packed layers, which form a
regular lattice structure.
The outer electrons of the metal
atoms separate from the atoms
and create a ‘sea of electrons’.
These electrons are delocalized
and are free to move through
the structure. The metal atoms
become positively charged ions and
are attracted to the sea of electrons.
This strong attraction is
called metallic bonding.
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sea of electrons
metal ions
© Boardworks Ltd 2011
Metallic structures
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© Boardworks Ltd 2011
4 marks
Why do metals have high
melting and boiling points?
Gold, for example, has a
melting point of 1064 °C and a
boiling point of 2807 °C.
- Strong forces of attraction
- Between positive ions and negative
electrons
- Sea of delocalised electrons
- As metallic bonds are so strong a large
amount of force is needed to break them
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© Boardworks Ltd 2011
Properties of metals: conductivity
Can you explain why metals conduct? Think about
metallic bonding.
Metals are good conductors of:
 heat – the free electrons can take in heat energy, which
makes them move faster. They can then transfer the
energy throughout the lattice.
 electricity – the free electrons can carry an electrical
charge.
Silver is the best conductor of
electricity and copper is the
second best.
Why is copper used instead of
silver for electrical wires?
Can you explain why some
metals are more conductive?
• Do you think the length or diameter of a
wire will affect its conductivity? Why?
• How could you test this?
What is resistance? – Rough Notes
Electricity in wires is a flow of electrons along the wire. As the electrons
move along the wire they collide with the metal atoms (positive ions). The
negative electrons get attracted to the positive ions; so if there are more
of them (e.g. in a longer wire) there is more resistance, as the electrons
have to pass more positive ions – this is called electrostatic resistance.
Resistance is a measure of how much a material tries to stop
electricity passing through it.
Properties of metals: density
Metal ions form a lattice which is more tightly packed and
denser than the lattices in ionic compounds
Metals generally have a very high melting and boiling point
because metallic bonds are very strong and so a large
amount of energy is needed to break them.
Strength
Layers of atoms can slip over each other in metal grains when
a force is applied, but this slippage stops at grain boundaries.
grain boundary: where
one grain meets another
The smaller the grains, the shorter the distance the atom
layers can move. This means that metals with smaller grains
are stronger and harder than metals with larger grains.
Which metals have small grains?
The faster that molten metal is cooled, the smaller the
grain size.
Properties of metals: strength
Metals are usually tough, not brittle. When a metal is hit, the
layers of the lattice just slide over each other. The metallic
bonds do not break because the electrons are free to move.
force
When the ions move the electrons distribute themselves
evenly so the ions don’t repel like in ionic compounds
This means that metals are:
 malleable – they can be bent and pressed into shape;
 ductile – they can be drawn out into wires.
Strengthening metals
Metals can be made stronger by adding another element
when the metal is molten. The atoms of the new element
spread through the crystal structure.
force
force
Because the atoms of the added element are larger, they
make it difficult for layers of metal atoms to slide. This
makes the metal less malleable and less ductile.
This process is called alloying, and the new substance is
called an alloy.
Different types of alloys
Adding different elements to metals creates different alloys,
with different properties.
Usually, other metals are added, for example:
 zinc, magnesium and copper are added to
aluminium to create an alloy that is light but very
strong. This is used in building aircraft.
 chromium and nickel are added to iron to make
stainless steel, which is resistant to corrosion.
 tin and lead are mixed together to create
solder, which has a low melting point and is
used to join other metals together.
Metals and metallic bonding
Multiple-choice quiz