Question

Brief explanation of Fajan’s rule applications

(I) the relationship between beryllium and Boron with aluminum and silicon

Answer 1

Covalent character in an ionic compound can be determined by Fajans rule. According to this rule covalent character is more in:

1) Ions having more charge that is cations having more positive charge and anions having more negative charge.

2) Cation has small ionic radius.

3) Anion having large ionic radius.

Note: Greater is the polarisation, greater is the covalent character.

Relationship between beryllium and aluminum:

In the periodic table beryllium lies in the 2nd group and 2nd period, Al lies in the 3rd group and 3rd period. But they resemble a lot in their properties. They almost have same charge to radius ratio and same electronegativity. So, according to Fajan's rule, they will have same polarizing power. They prefer to form covalent compounds over ionic ones.

Similarly, boron resemble silicon in various properties. This can also be explained using fajan rule. They both have almost same charge to radius ratio and electronegativity. They also have same electronegativity.