Silicon dioxide, SiO2 , and silicon(IV) chloride, SiCl4 , are both covalently bonded compounds.The table shows the melting and boiling points of these two compounds, and the physical state of silicon dioxide at room temperature. Compound Melting point in °C Boiling point in °C Physical state at room temperature SiO2 1710 2230solid SiCl4 −6958(i) Complete the table by giving the physical state of silicon(IV) chloride at room temperature. (1)(ii) Explain, in terms of structure and bonding, why silicon dioxide has a much higher melting point than silicon(IV) chloride.(6)

(i) The physical state of silicon(IV) chloride at room temperature is gas. This is because its boiling point is -69.5°C, which is much lower than room temperature.

(ii) Silicon dioxide has a much higher melting point than silicon(IV) chloride due to its structure and bonding. Silicon dioxide has a giant covalent structure, meaning it consists of a large number of silicon and oxygen atoms covalently bonded together in a three-dimensional network. This type of structure requires a large amount of energy to break down, hence the high melting point.

On the other hand, silicon(IV) chloride consists of simple molecules with weak van der Waals forces between them. These forces are much easier to break, requiring less energy and thus resulting in a lower melting point.