Polarisation of ionsEdexcel International A Level Chemistry: Mind map

Exam questions on Polarisation of ions

1. A teacher gives the following ionic radii: Na⁺ 0.102 nm, K⁺ 0.138 nm, Mg²⁺ 0.072 nm and Al³⁺ 0.054 nm. She asks the class to compare how strongly each cation distorts the electron cloud of a neighbouring anion.
   Explain why Al³⁺ has a greater polarising power than Na⁺.2 marks
2. Lithium forms the halides LiF, LiCl, LiBr and LiI. The ionic radii of the anions are: F⁻ 0.133 nm, Cl⁻ 0.181 nm, Br⁻ 0.196 nm and I⁻ 0.220 nm. The sulfide ion, S²⁻, has a radius of 0.184 nm.
   Explain why the sulfide ion is more polarisable than the chloride ion.2 marks
3. Lithium iodide and sodium iodide are both classed as ionic, but lithium iodide shows more covalent character. Aluminium iodide, AlI₃, has a melting point of only 191 °C, which is low for a compound of a metal with a non-metal. Ionic radii: Li⁺ 0.076 nm, Na⁺ 0.102 nm, Al³⁺ 0.054 nm and I⁻ 0.220 nm.
   Explain why the iodide ion is distorted more in lithium iodide than in sodium iodide.3 marks