4.5 Metallic Bonding

Syllabus

 

 

 

    Understanding

Metallic Bonds are electrostatic attractions between positive metal ions and delocalised electrons

Relative Strength: Depends on the charge  and radius of the ions

Alloys contain more than one metal and this affects their properties

 

 

Skills

Explain trends in melting points of metals

Explain Electrical conductivity and malleability of metals

Explain properties of alloys

 

Nature 

of Science

 

Theories explain natural phenomena – properties of metals are different to both ionic and covalent substances



What does this mean?

What is a metallic bond?

All metal atoms need to lose electrons.

But without any non-metal atoms they have nothing to give the electrons to.

The solution is for all metal atoms to lose electrons (and become positive ions) which are then surrounded by a “sea of delocalised electrons”.

The ions repel each other, but they are closer to the electrons so the attractions outweigh the repulsions.



Metallic Bonding



Properties of metals

Because the electrons are delocalised (not fixed in position) they can move about – making metals good electrical conductors.

Because the bonds are not fixed in position (are non-directional) they don’t break if the shape of the lattice changed – eg by hammering or rolling. So metals are malleable.



Questions.

 

1.      All Alkali metals form 1+ ions. Suggest why their melting points vary as shown. 

 

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   2.      Suggest two reasons why the melting points of Sodium, Magnesium and Aluminium  vary in the way shown.


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Alloys


An alloy is one metal mixed with at least one other element (often but not always another metal)

Pure metals are often rather soft and overly malleable/ductile.

This is because the atoms build up crystals in layers that slide over each other.

Alloying mixes in other atoms, either much bigger or much smaller and this disrupts the layer structure.



Steel is an alloy of Iron and Carbon.

 

Why is it so much stronger than Iron?

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Alloys


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