Silicon dioxide has a giant molecular structure, consisting of a large number of silicon and oxygen atoms covalently bonded to form a big tetrahedral structure. A lot of energy is needed to break the strong covalent bonds, resulting in the high melting point and boiling point of silicon dioxide.
Category: Structure and Properties of Materials
Explain why alloys have different physical properties from their constituent elements.
When other elements are added to the pure metal, the different atomic sizes of the different elements disrupt the regular arrangement of the pure metal atoms. This irregular arrangement of the different atoms results in the alloys having different physical properties from their constituent elements. When a force is applied, the atoms in an alloy cannot slide over one another easily, causing the alloy to have lower malleability, lower ductility and higher strength as compared to pure metal.
Explain, using structure and bonding, why diamond is very hard.
Diamond has a giant molecular structure. It consists of a large number of carbon atoms covalently bonded to one another to form a giant tetrahedral structure. This structure is a strong and rigid structure, making diamond very hard.
Explain, using structure and bonding, why graphite can conduct electricity.
Graphite has a giant molecular structure. It is made up of layers of carbon atoms covalently bonded. Each layer is made up of carbon atoms covalently bonded to one another in hexagonal rings. Each carbon atom is covalently bonded to 3 other carbon atoms, hence each carbon atom has 1 valence electron not involved in bonding. These electrons are delocalised, and can move freely within the layer to conduct electricity.