Question

Explain the following briefly.

a) Inert pair effect
b) Hydration enthalpy
c) Atomisation enthalpy
d) Lanthanide contraction
e) Actinide contraction.​

Answer 1

Answer:

$\longmapsto \sf\boxed{\bold{\pink{Explain\: the\: following\: briefly\: :-}}}$

${\large{\bold{\purple{\underline{a)\: Inert\: pair\: effect\: :-}}}}}$

$\implies$ The elements of 4th , 5th and 6th period of the p-block elements which comes after d-block elements, the electrons present in the intervening d- or f- orbitals do not shield the s-electrons of the valence shield effectively. As a result, $\sf {ns}^{2}$ electrons remain more tightly held by the nucleus and hence do not participate in bonding. This is called inert pair effect.

$\rule{150}{2}$

${\large{\bold{\purple{\underline{b)\: Hydration\: enthalpy\: :-}}}}}$

$\implies$ It is the amount of energy released when one mole of gaseous ions combine with water to form hydrated ions. This is called hydration enthalpy.

$\rule{150}{2}$

${\large{\bold{\purple{\underline{c)\: Atomisation\: enthalpy\: :-}}}}}$

$\implies$ The enthalpy change accompanying the association of all the molecules in one mole of gas phrase substance into gaseous atoms is called atomisation enthalpy.

$\rule{150}{2}$

${\large{\bold{\purple{\underline{d)\: Lanthanide\: contraction\: :-}}}}}$

$\implies$ In a lanthanide, there is a regular decrease in the size of atoms and tripositive ions with increase in atomic number. This decrease of ionic and atomic radii in the lanthanide elements is called lanthanide contraction.

$\rule{150}{2}$

${\large{\bold{\purple{\underline{e)\: Actinide\: contraction\: :-}}}}}$

$\implies$ The steady decrease in atomic size of the actinides with increase in the atomic number. This is called actinides contracting.

$\rule{150}{2}$

EXTRA INFORMATION :-

$\diamondsuit$ Inert pair effect is prominent character is Pottasium (k) .

$\diamondsuit$ Hydration enthalpy of alkali metals decrease with increase in ionic size.

Answer 2

Aɴsᴡᴇʀ :

INERT PAIR EFFECT :

This is a peculiar effect characterised by non-sharing of the valence electrons (i.e. inability of the valence electrons from "s" shells of the lower groups to take part in bonding).

Usually occurs in lower periods of group 11, 12 and 13, due to poor shielding effect on the ns² electrons by the inner "d" and "f" orbitals.

Example: Tin, Lead and Bismuth shows this effect resulting in lower oxidation states.

HYDRATION ENTHALPY:

Hydration enthalpy is the amount of energy released upon hydration (surrounded by water molecules) of 1 mole of a compound.

In other words, it is an index of stability of a compound. Higher the hydration enthalpy, higher will be the energy released and more will be the stability.

ATOMISATION ENTHALPY:

This is the energy required to break down all the components of a compound into individual elements.

Since, heat has to supplied, value of ∆H_(at) will be positive.

LANTHANIDE CONTRACTION:

The steady decrease in the atomic/ionic radii of the elements of LANTHANIDE series staring from Lanthanum is called Lathanide Contraction.

As we move from left to right in that period, valence electrons start to experience imperfect shielding effect of 4f orbital.

As a result, the nucleus pulls the valence electrons with greater force and reduces the atomic radii.

ACTINIDE CONTRACTION:

The steady decrease in the +3 oxidation state of the ACTINIDE series of elements with increase in atomic number is called ACTINIDE CONTRACTION.

The main cause of ACTINIDE CONTRACTION is inadequate shielding by 5f electrons.