Magnesium silicide, Mg₂Si, is a compound made by heating magnesium with sand.

1. (a)Draw a 'dot-and-cross' diagram to show the arrangement of outer electrons present in a formula unit of Mg2Si. Assume magnesium silicide is an ionic compound.[2]
2. (b)When solid Mg2Si is added to water, silane gas, SiH4, and a solution of magnesium hydroxide are produced. Construct the equation for this reaction. Include state symbols.[2]
3. (c)Suggest, with reference to structure and bonding, why SiH4 is a gas at room temperature.[2]
4. (d)(i)C-H and Si–H bonds have weak dipoles. Use the electronegativity values in the table to show the polarity of the C-H and Si-H bonds. C-H Si-H[2]
5. (d)(ii)Explain why methane, CH4, has no overall dipole moment.[2]
6. (e)SiH4 reacts in air without heating but CH4 must be ignited before combustion occurs. SiH4 + 2O2 → SiO2 + 2H2O CH4 + 2O2 → CO2 + 2H2O Suggest, with reference to bond energies from the Data Booklet, why SiH4 reacts in air without heating but CH4 must be ignited.[2]
7. (f)(i)Identify the two products formed during this reaction.[2]
8. (f)(ii)Describe the behaviour of the silicon dioxide during this reaction.[1]