KS4 Chemistry Metallic Bonding

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Metallic bonding Atoms of metals are tightly packed together in a giant lattice similar to the lattice in ionic compounds. sea of free electrons metal atoms metal ions 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. This attraction is called metallic bonding and is the reason why the positive metal ions do not repel each other.

Electrons and metallic bonding How is the sea of electrons involved in metallic bonding?

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. Mercury has the lowest melting point of all metals, -39°C, and is liquid at room temperature. Sodium melts at 98°C.

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?

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 This means that metals are: malleable – they can be bent and pressed into shape; ductile – they can be drawn out into wires.

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

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. 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.