Chemistry 9701 · AS & A Level · Atoms, molecules and stoichiometry
Atoms, molecules and stoichiometry — practice question
The elements from sodium to sulfur react with chlorine. The melting points of several chlorides that are formed are shown.
chloride: NaCl, MgCl$_2$, AlCl$_3$, SiCl$_4$, PCl$_3$, SCl$_2$
melting point / K: 1074, 987, 463, 203, 161, 195
(a)[4]
Predict the shapes of AlCl$_3$ and PCl$_3$. Use diagrams to show the shapes, name the shapes and state the bond angles.
(b(i))[3]
Explain, in terms of structure and bonding, why the melting point of SiCl$_4$ is much lower than that of NaCl.
(b(ii))[2]
Explain why SiCl$_4$ has a higher melting point than PCl$_3$.
(b(iii))[1]
Draw the dot-and-cross diagram for one SiCl$_4$ molecule. Show only the outer electrons.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Accurate diagram of $\\text{AlCl}_3$ showing trigonal planar shape and bond angle $120^\\circ$” …