Question

Amongst \[\text{LiCl, RbCl, BeC}{{\text{l}}_{2}}\text{ and MgC}{{\text{l}}_{2}}\]the compounds with the greatest and the least ionic character, respectively are:
A. \[\text{LiCl and RbCl}\]
B. \[\text{RbCl and BeC}{{\text{l}}_{2}}\]
C. \[\text{BeC}{{\text{l}}_{2}}\text{ and MgC}{{\text{l}}_{2}}\]
D. \[\text{RbCl and MgC}{{\text{l}}_{2}}\]

Answer 1

Hint: For this problem, we have to study the concept of the Fajan's rule i.e. by determining cation and anion and due to which we can easily explain which compound will have the greatest and lowest ionic character.

Complete step by step solution:
- In the given question, we have to explain that among the given molecules which have the greatest and the least ionic character.
- As we know that cation is the species which consist of positive charge whereas anion is the species which consist of negative charge.
- Now, according to the Fajan's rule, the molecule which consists of large-sized cation and small-sized anion then the molecule will have high ionic character.
- Also, ionic character and covalent character have an inverse effect on each other so whenever the ionic character increases then covalent character decreases.
- Now, among the given options Rubidium has the largest size because, in the periodic table, it is placed down as compared to the beryllium, magnesium and lithium.
- And also has more electronegativity due to which rubidium chloride will have the maximum ionic character.
- Now, beryllium cation will have the smallest size and also have less electronegativity due to which it has less ionic character and has a high covalent character.

Therefore, option B is the correct answer.

Note: In the given problem, after rubidium chloride lithium chloride will have the maximum ionic character and then magnesium chloride. Lithium will be more ionic because down the group electronegativity decreases and magnesium is placed below to the lithium.