1.45 explain how the uses of diamond and graphite depend on their structures, limited to graphite as a lubricant and diamond in cutting.

In Graphite the atoms from layers, these layers can slide over each other, this makes it very slippery and so can be used as a lubricant.

Diamond is extremely hard because it has a many bonds in it, this means it is great for cutting as it can cut anything.

1.44 draw diagrams representing the positions of the atoms in diamond and graphite

chem.ufl.edu

Carbon atoms in Graphite (left), are each bonded to three other atoms.

Diamond (right) is formed of carbon atoms each joined to four others.

1.43 explain the high melting and boiling points of substances with giant covalent structures in terms of the breaking of many strong covalent bonds

A giant covalent structure is one with many atoms bonded together. To melt or boil them you are not separating intermolecular bonds (between molecules), you are separating intramolecular bonds that keep the molecule together. These bonds are strong covalent bonds which take a lot of energy to break, so a lot of heat energy is required before the bonds will break to boil or melt; meaning they have high melting and boiling points.

1.42 explain why substances with simple molecular structures have low melting and boiling points in terms of the relatively weak forces between the molecules

A substance with a simple molecular structure is one that contains only a few atoms in a molecule.
The intermolecular forces (between the molecules) are weak, so it doesn't take much energy- or heat- to break them- this means they will melt and boil under low heats, as even small amounts of heat energy are enough to break the bonds.

1.41 understand that substances with simple molecular structures are gases or liquids, or solids with low melting points

A simple molecule (one with only a few atoms) will have a low melting point.

1.40 explain, using dot and cross diagrams, the formation of covalent compounds by electron sharing

To draw a dot and cross diagram for a covalent bond, you need to draw the outer shells of the two atoms involved with an overlap, in this overlap should be the electrons they share. Half the electrons in the overlap should be dots and half crosses, because one electron in every pair comes from each atom. The rest of the electrons for the outer shell should be drawn on, one atom with dots, the other with crosses.

For example, H + Cl = HCl:

You need to be able to do dot and cross for the following substances (comment if you need help with any):

i hydrogen

ii chlorine

iii hydrogen chloride

iv water

v methane

vi ammonia

vii oxygen

viii nitrogen

ix carbon dioxide

x ethane

xi ethene

1.39 understand covalent bonding as a strong attraction between the bonding pair of electrons and the nuclei of the atoms involved in the bond

Electrons, being shared by atoms in a covalent bond, are attracted to the nucleus of each atom in the bond. Remember that electrons are negative and protons- in the nucleus- are positive.

1.38 describe the formation of a covalent bond by the sharing of a pair of electrons between two atoms

A covalent bond is a bond formed between atoms by sharing a pair of electrons (one from each atom.)