Understanding metals

Why are metals used to make these items?

Properties of metals

What property of metals is being utalised in the images on the previous slide?• Fishing sinker• Cooking pot• Electrical wires• Bread ties• Mirror• Car body

Metallic bonding modelHow can we explain the properties exhibited by metals?

What do thesilver spheres represent?

What do thered spheres represent?

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Metals form a crystal latticeEach metal atom loses outer shell electrons to form a positive cation

The cations form a rigid framework:“a lattice of cations”

“a sea of delocalised electrons” The electrons move freely through the lattice:

Delocalised: able to move freely, not fixed to one atom

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The lattice is held together by the strong electrostatic attraction between cations and delocalised electrons

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Metal cations pack to form crystalsThey form regular geometric patterns:

body – centred cubicco-ordination no.: 8(Na, K, Cr, Ba)

face – centred cubicco-ordination no.: 12(Au, Ag, Cu, Al)

hexagonal close packingco-ordination no.: 12(Ti, Zn, Mg)

Explaining properties of metals

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Metals are hard, with a high melting point

Due to the strong electrostatic attraction between cations and delocalised electrons

Metals are dense

Due to the close packing of the cations in the lattice

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Metals conduct electricity

The delocalised electrons are able to move freely through the lattice and carry electrical charge.

Metals conduct heat

Electrons move faster when heated, they can carry the energy through the lattice

Metals are lustrous

They are shiny when polished: the delocalised electrons are able to reflect light.

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Metals are malleable and ductile (not brittle)

Malleable: able to be beaten into a sheet

Layers of atoms can slide past each other: the delocalised electrons can move with them to maintain the electrostatic attraction

Ductile: able to be drawn into a wire

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Questions

Explain the following properties of copper:a) Hard

b) Malleable and ductile

c) Good electrical conductor

d) lustrous when polished

The electrostatic attraction between the metal cations and delocalised electrons is very strong

When layers of cations are distorted, delocalised electrons are able to move to maintain the electrostatic attraction

The delocalised electrons are free to move and carry charge through the metal

The delocalised electrons reflect light

Alloys

• Mixing metals can change their properties. There are two main types of alloys.

• Substitutional alloys those made from metals of a similar size where the second metal takes the place of the first in the lattice.