Question

Explain the following briefly.

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

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.

$\star$ Hope It Helps.