College of Professional and Continuing Education \( 1 \mathrm{OHO}_{\mathrm{H}}^{\mathrm{L}} \)
Answer ALL questions in the answer book provided.
Question 1
(a) Magnesium \( (\mathrm{Mg}) \) has an atomic number of 12 and an atomic mass of \( 24.31 \mathrm{~g} / \mathrm{mol} \).
(i) Write the full electron configuration with details of sub-shells for the element calcium,
(3 marks)
(ii) Determine the number of valence electrons in 3 g of pure magnesium.
(5 marks)
(iii) Magnesium oxide ( MgO ) is formed by magnesium ion \( \mathrm{Mg}^{2+} \) and oxide ion \( \mathrm{O}^{2-} \), calculate the attraction energy between a \( \mathrm{Mg}^{2+} \) and a \( \mathrm{O}^{2-} \) with a separating distance of 1.7 nm .
(6 marks)
(b) Tungsten (W) has a body-centered cubic (BCC) crystal structure.
(i) Determine the number of tungsten atoms in two tungsten unit cells.
(2 marks)
(ii) Given the atomic radius of tungsten is 0.136 nm , determine the volume of its unit cell.
(4 marks)
(iii) Given the atomic mass of tungsten is \( 183.84 \mathrm{~g} / \mathrm{mol} \), determine the mass (in gram) of one tungsten specimen with a total volume of \( 5 \mathrm{~cm}^{3} \).
(5 marks)
(Total: 25 marks)
