Structure

The type of structure an element forms is due to the

nature of its bonding.

Metallic structures

Metal cations (not atoms)

Surrounded by a “sea” of delocalised electrons

The attraction of the +ve ions for the delocalised electrons forms the metallic bond.

Giant metallic lattices

Metal cations are arranged in a regular structure.

As the metallic bond is strong metals have high MPs and BPs and are solid at RTP.

Electrical conductivity

Delocalised electrons are free to move.

So metals conduct when solid.

Mallability

Due to the regular arrangement of layers of metal cations metals can be beaten into thin sheets.

Ductility

Ductility

Metals can be drawn out into fine wires.

Non-metal structures

• There are three types of non-metal structures;

• 1) Giant covalent (molecular) lattices• Eg; Carbon and silicon.• 2) Simple covalent (molecular) lattices• Eg; Most other non-metals • 3) Simple atomic lattices.• Eg; All inert gases.

Carbon has two physical forms

(allotropes).

1) Diamond

2) Graphite

1) Diamond Tetrahedra of C atoms covalently linked to four others.

Strong covalent bonds mean a high MP and BP.

Electrons tied up in bonds, atoms not ions, so will not conduct electricity.

2) Graphite

The fourth electron is delocalised over the hexagon layer.

Giving weak van der Waals forces between layers.

Each C is covalently bonded to 3 others, forming a flat layer of hexagons.

Due to the fourth, delocalised electron, which is free to move, graphite is a conductor.

Weak van der Waals forces are easily broken, allowing the layers to slide past each other.

Leaving a mark on paper.Hence graphite’s name, which comes from the Greek for writing

Pencils – not lead but graphite!

Other Giant Covalent Lattices

• Silicon dioxide, aka quartz, and silicon carbide also form giant covalent lattices.

Another form of silicon dioxide is flint, used for prehistoric tools;

Simple covalent lattices

Molecules held together by weak van der Waals forces.

Physical states

Van der Waals forces are weak so many covalent substances, such as chlorine (Cl2) are liquids or gases at RTP.

They only form a solid simple covalent lattice at low temperatures.

But in larger molecules, or atoms, the cumulative van der Waals forces may be sufficient for the substance to be solid at RTP.

Eg The other halogens are gases, or liquids, but iodine (I2) is a solid.

Phosphorous forms tetrahedra (P4) and is a red solid

Sulphur forms a ring of 8 atoms

Sulphur (S8) forms yellow crystals.

Simple atomic lattices

• At very low temperatures the inert gases form simple atomic lattices.

• The van der Waals forces between their atoms are weak, therefore they are easily broken.