Periodic Properties

Atomic Size

Atomic size is the distance between the centre of nucleus and the outermost shell of an isolated atom. It is also known as atomic radius. The size of atoms decreases from left to right in a period but increases from top to bottom in a group.

(i) Atomic radii

The distance from the centre of the nucleus to the outermost shell containing electrons called atomic radius.

It is not possible to measure the absolute value of atomic radius of an element. However, it may be expressed in three different form covalent radii, metallic radii, Van der wall radii.

Van der wall radii > metallic radii > covalent radii

(ii) Ionic radii

The effective distance from the centre of nucleus of the ion upto which it exerts its influence on the electron cloud is called ionic radii.

Anionic radii > atomic radii > cationic radii

(iii) Ionization Potential (I.P.)

The amount of energy required to remove an electron from isolated gaseous atom is called Ionization Potential (I.P.) or Ionization Energy (I.E.)

A (g) - e + Energy required (I.P.) ―→ A⁺ (g)

(iv) Electron affinity (E_a)

The energy released during addition of an extra electron in isolated gaseous atom is called electron Affinity.

A (g) + e ―→ A^- (g) + Energy released

Chlorine (Cl) has highest E_a value.

(v) Electronegativity (E_n)

The relative electron attracting tendency of its atom for a shared pair of electrons in a chemical bond is called electronegativity.
F is the most electronegative atom

E_n = ( IP + E_a ) / 5.6

E_n value > 1.7 (ionic compound)
E_n value < 1.7 (polar covalent compound)
E_n value = 0 (nonpolar compound)

(vi) Lattice Energy

The amount of energy released during formation of one mole of ionic compound from its constituent ions is called Lattice energy.

(vii) Hydration Energy

The amount of energy released during dissolution of one mole of compound into water, is called hydration energy.

If hydration energy > Lattice energy, then compound is soluble in water and
if hydration energy < Lattice energy, then compound is insoluble in water.

Metallic and Non-metallic Character

The tendency of an element to lose electrons to form cations is called electropositive or metallic character of an element. Alkali metals are most electropositive. The tendency of an element to accept electrons to form anions is called electronegative or non- metallic character of an element.

1. Variation of Metallic Character in a Group

Metallic character increases from top to bottom in a group as tendency to lose electrons increases. This increases the electropositive character and metallic nature.

2. Variation of Metallic Character in a Period

Metallic character decreases in a period from left to right. It is because the ionization energy increases in a period. This decreases the electropositive character and metallic nature.

Valenc

It is the combining capacity of an element, and it increases from 1 to 7 along a period with respect to oxygen, whereas, with respect to hydrogen, it first increases from 1 to 4, and then decreases to 0.

Ionisation Energy

It is the energy required to remove an electron from the outermost shell of an isolated gaseous atom. It generally increases along a period from left to right. And generally decreases along a group on moving downwards.

Electron Affinity

It is defined as the energy liberated when an extra electron is added to an atom. Generally, it increases across a period from left to right but electron affinity of 112. 15 group and 0 group is 0 or positive. Electron affinity decrease on moving down a group.

Oxidation State

It is the hypothetical charge that an atpm would have if all bonds to atoms of different elements were removed. It is typically represented by integers, which can be positive, negative, or 0.