Giant covalent structures
Giant covalent structures contain very many All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons., each joined to adjacent atoms by A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.. The atoms are usually arranged into giant regular A regular grid-like arrangement of atoms in a material. 鈥 extremely strong structures because of the many bonds involved.
The graphic shows the molecular structure of graphite and diamond (two A different form of the same element in the same state. For example, diamond and graphite are allotropes of carbon. of carbon).
Properties of giant covalent structures
- Very high melting points 鈥 this is because a lot of strong covalent bonds must be broken. Graphite, for example, has a melting point of more than 3,600掳C.
- Variable electrical conductivity 鈥 diamond does not To allow electricity, heat or other energy forms to pass through. electricity, whereas graphite contains free Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. so it does conduct electricity. An element in Group 4, with the chemical symbol Si. is a semi-conductor 鈥 it is midway between non-conductive and conductive.
Graphite
Graphite is a form of carbon in which the carbon atoms form covalent bonds with three other carbon atoms. This means that each carbon atom has a 鈥榮pare鈥 electron (as carbon has four outer electrons) which is When an electron is not associated with a particular atom, eg the outer electrons in a metal can be free to move through the solid. between layers of carbon atoms. These layers can slide over each other, so graphite is much softer than diamond. It is used in pencils, and as a A lubricant is anything which reduces the friction between two surfaces.. Graphite conducts electricity due to the 鈥榮pare鈥 electrons being delocalised between the layers. This conductivity makes graphite useful as electrodes for The decomposition (breakdown) of a compound using an electric current..
However, graphite still has a very high melting and boiling point because the strong covalent bonds that hold the carbon atoms together in the layers require a lot of heat energy to break.
Diamond
Diamond is a form of carbon in which each carbon atom is joined to four other carbon atoms, forming a giant covalent structure. As a result, diamond is very hard and has a high melting point. This explains why it is used in cutting tools. It does not conduct electricity as there are no delocalised electrons in the structure.
Silica (or silicon dioxide), which is found in sand, has a similar structure to diamond, so its properties are similar to diamond. It is hard and has a high melting point, but contains silicon and oxygen atoms, instead of carbon atoms.