3.2 (c) Macromolecules

3.2 (c) Macromolecules

Diamond: has four bonds, high melting point, does not conduct and is very hard. Used for cutting, because it is the hardest known substance (2 left pictures below).

Graphite: has three bonds, made of flat sheets that are held together by weak forces so it is soft and slippery, so it is used as a lubricant. It can conduct electricity because it has one free electron. It is slippery because the sheets have week bonds between them (middle picture).

Silicon (IV) oxide/silicon dioxide/silica: makes up most of sand. Each Si atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms. As a result it has a high melting point and is hard, like diamond (right picture).

Silicon IV oxide and diamond both have high melting points and are very hard substances.

GENERAL PROPERTIES OF GIANT  MOLECULES

MELTING POINT – Very high since structure is made up of a large number of covalent bonds, all of which need to be broken if atoms are to be separated

ELECTRICAL – Don’t conduct electricity – have no mobile ions or electrons, BUT… Graphite conducts electricity STRENGTH – Hard – exist in a rigid tetrahedral structure e.g. Diamond and silica (SiO2)… but Graphite is soft