Question

Which of the following substances would you predict to be a) most ionic, b) most covalent, and c) most metallic?

Answer choice #1: a) NaF b) CCl4 (c) Rb

Answer choice #2: a) AlCl3 b) SiCl4 (c) Mg

Answer choice #3: a) MgO b) PF5 (c) K

Answer 1

The covalent character of ionic compounds is governed by the Fajan’s rules. According to the Fajan’s rule, the cation with the higher positive charge and lower size impart greater covalent character than the cation with lower positive charge and higher size.

Choice 1: a) NaF b) CCl4 (c) Rb

In NaF, the charge of cation is +1
In CCl₄ the charge of cation is +4
Therefore according to Fajan’s rule, NaF is most ionic (least covalent) and CCl₄ is most covalent (least ionic).
In Rb metallic bonding is present. Therefore Rb is most metallic

Choice 2: a) AlCl₃ b) SiCl₄ (c) Mg

In AlCl₃, the charge of cation is +3
In SiCl₄ the charge of cation is +4
Therefore according to Fajan’s rule AlCl₃ is most ionic(least covalent) and SiCl₄ is most covalent (least ionic)
In Mg metallic bonding is present. Therefore Mg is most metallic.

Choice 3: a) MgO b) PF₅ (c) K

In MgO, Here the charge of cation is +2
In PF₅ the charge of cation is +5
Therefore according to Fajan’s rule, MgO is most ionic(least covalent) and PF₅ is most covalent (least ionic)
In K metallic bonding is present. Therefore K is most metallic