(I) Mention any two anomalous properties of second period elements? (

(I) Mention any two anomalous properties of second period elements? (II) Arrange Na+ , Mg2+ and Al3+ in the increasing order of ionic radii. Give reason?

Answer»

(I) Anomalous properties of second period elements:

1. In the 1^st group, lithium forms compounds with more covalent character while the other elements of this group form only ionic compounds.

2. In the 2^nd group, beryllium forms compounds with more covalent character while the other elements of this family form only ionic compounds.

(II) Na⁺ , Mg²⁺ and Al³⁺ are isoelectronic cations.

Ions	Na⁺	Mg²⁺	Al³⁺
Number of electrons	10	10	10
Number of Nuclear charge	11	12	13

The cation with the greater positive charge will have a smaller radius because of the greater attraction of the electrons to the nucleus. Hence the increasing order of ionic radii is, r_Na⁺, > r_Mg²⁺, >r_Al³⁺

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