Structure and bonding

What are ionic compounds ?

Ionic compounds are giant structures of ions

What happens n a giant ionic lattice?

In a giant ionic lattice, there are very strong forces of attraction between the positive and negative ions. These strong electrostatic forces of attraction hold the positive and negative ions in place. The electrostatic forces are also called ionic bonds and they act in all directions.

What are the properties of ionic compounds ?

• High melting and boiling points because the strong electrostatic forces of attraction require a great deal of heat energy

• They cant conduct electricity when they are solid. This is because the ions are locked in place by the strong electrostatic forces of attraction. However, they can conduct electricoty when they are melted or dissolved in water, thats because the ions are now able to move and carry the charge around the whole structure.

Limitation of dot and cross diagram :

• They dont tell you the shape of the molecule

Limitation of two dimensional stick

• Unable to tell which electron in the covalent bond came from which atom

Limitation of ball and stick

• The ions are widely spaced but in reality they are packed together

what happens in small molecules ?

In small molecules oeach molecule only contains a few atoms with strong covalent bonds between these atoms. Different molecules have weak intermolecular forces of attraction. For example water

What are properties of small molecules ?

• Low melting and boiling point because only the intermolecular forces need to be overcome to melt or boil the substances. Not the bonds between the atoms. This requires very little energy due to the intermolecular forces of attraction being very weak.

• Gas or liquid at room temperature

What are polymers ?

They have large molecules. The atoms in polymers are linked to other atoms by strong covalent bonds

What are properties of polymers ?

• Strong intermolecular forces of attraction which require lots of energy to overcome

• Solid at room temperature

What are giant covalent structures ?

All the atoms in these structures are linked to other atoms by strong covalent bonds

What are properties of giant covalent structures ?

Relatively low intermolecular forces of attraction which require little energy to be broken

Solid at room temp

What is the structure of graphite ?

Graphite is a giant covalent structure.

Made only of carbon and each carbon atom bonds to three others forming hexagonal rings in layers. Each carbon atom has one spare electron which is delcolised therefore free to move around the whole structure.

what is the hardness of graphite ?

The layers can slide over eachother because they are no covalently bonded therefore are held together weakly, making it relatively soft when compared to daimond.

What is the conductivity of graphite ?

The layers can slide over eachother because they are no covalently bonded therefore are held together weakly, making it relatively soft when compared to daimond.

What are nanotubes ?

The carbon atoms in nanotubes are made of cylindrical tubes. There tensile strength makes them good in electronics

What is graphene ?

Made of one layer of graphite. Its strong covalent bonds is they are a strong material that conducts electricity. They are useful as composites and high tech electronics.