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KS4 Chemistry

Metallic Bonding

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Metals in the periodic table

Metal are found at the left and centre of the periodic table.

H He

Rn

Xe

Kr

Ar

Ne

Ra Ac Rf Db Sg Bh Hs Mt Ds Rg ? ? ? ? ? ? ?

Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At

Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I

Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br

Mg Al Si P S Cl

Be B C N O F

Cs

Rb

K

Na

Li

Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg

Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po

Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn

Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga

Mg Al

Be

Cs

Rb

K

Na

Li

Fr

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Atoms of metals are tightly packed together in a giant lattice similar to the lattice in ionic compounds.

This attraction is called metallic bonding and is the reason why the positive metal ions do not repel each other.

The outer electrons separate from their atoms and become delocalized, creating a ‘sea of electrons’. The atoms become positive ions and are attracted to these electrons.

metal atoms

sea of free electrons

metal ions

Metallic bonding

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Electrons and metallic bonding

How is the sea of electrons involved in metallic bonding?

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Properties of metals: density

Metal ions form a lattice which is more tightly packed and denser than the lattices in ionic compounds. They form crystals called grains.

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.

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Properties of metals: conductivity

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?

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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.

malleable – they can be bent and pressed into shape;

force

ductile – they can be drawn out into wires.

This means that metals are:

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Metal grains

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 faster that molten metal is cooled, the smaller the grain size.

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.

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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.

This process is called alloying, and the new substance is called an alloy.

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.

force force

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Different types of alloys

Adding different elements to metals creates different alloys, with different properties. This affects how alloys can be used. 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.