Ionic size : - distance from the centre of the nucleus upto that place. Where the nuclear charge it being feet.

Ion is of two types

(i) Cation:-

Made by loss of electrons

→ Size of cation is always smaller than that of parent atom ∵ effective nuclear charge increases v the loss of e^- and sometimes even the shell is also lost.

Effective Nuclear Charge increases, size decreases

(ii) Anion:-

Formed by gain of electrons

→ Size of Anion is always large than that of parent atom ∵ with the gain of electron inlerelectronic repulsion increases and effective nuclear charge (E.N.C) decreases and size expands Effective Nuclear charge decreases, Size increases Increasing order of Size

(a) I⁺ < I < I^-

(b) Al⁺³ < Li (Exceptional)

(C) Mn⁺⁵ < Mn⁺³

Size of Cation = Internuclear ― Size of Anion distance

Higher the no. of e^Θ s lost, smaller is the size

Isoelectronic species:- There are those species which have same no of electrons. example- N^3-, Φ^2-, F^- Ne, Ae⁺³, Mg⁺², Na⁺ All have 10 electrons each.

The species having highest positive charge will be smallest in size among

isoelectronic species.

The species having highest negative charge will be largest in size among isoelectronic species

Example- The increasing order of sizes are:-

Al⁺³ < Mg⁺² < Na⁺ < Ne < F^- < O^2- < N^3-

Q (1) Write two isoelectronic species of:-

Rb,   F^-,   K,   Sc

(i) Kr, Rb, Sr⁺, Y²⁺         (iii) Ar, K, Cl⁺ Sc⁺²

(ii) F^-, Ne, Na⁺, Mg⁺²    (iv) Sc, Li⁺, V²⁺