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From the salts LiCl, RbCl, BeCl₂ and MgCl₂, which pair represents the compound with the highest ionic character and the one with the lowest ionic character, respectively?

1. LiCl and RbCl
2. RbCl and BeCl₂
3. MgCl₂ and BeCl₂
4. RbCl and MgCl₂

Correct answer: RbCl and BeCl₂

Solution

By Fajans' rules the large low-charge Rb+ gives RbCl the highest ionic character, while the small highly-polarising Be2+ makes BeCl2 the most covalent (lowest ionic character). So the pair is RbCl and BeCl2, not LiCl and RbCl.

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