Q49 of 59 Page 35

Discuss the factors affecting electron gain enthalpy and the trend in its variation in the periodic table.

The factors affecting electron gain enthalpy and the trend in its variation in the periodic table are:


1)ATOMIC SIZE


As we go down the group electron gain enthalpy decreases as the distance of the nucleus from the outermost shell increases which decreases its tendency to gain electron and electron gain enthalpy becomes less negative.


2)EFFECTIVE NUCLEAR CHARGE


As we go from left to right in a period the effective nuclear charge increases and when we move down the group it decreases which results in the attraction of electrons from the outermost shell.


3) ELECTRONIC CONFIGURATION


The tendency to gain electrons depends upon the stability of an element. Elements having completely or half filled stable orbitals have very low tendency to gain electron thus they have very low electron gain enthalpy.


TRENDS


Across a period: electron gain enthalpy becomes more negative.


Down the group: electron gain enthalpy becomes less negative.


More from this chapter

All 59 →
47

In the following questions a statement of Assertion (A) followed by a statement of reason

(R) is given. Choose the correct option out of the choices given below each question.


Assertion (A) : Boron has a smaller first ionisation enthalpy than beryllium.


Reason (R) : The penetration of a 2s electron to the nucleus is more than the 2p electron hence


2p electron is more shielded by the inner core of electrons than the 2s electrons.


(i) Assertion and reason both are correct statements but reason is not correct explanation


for assertion.


(ii) Assertion is correct statement but reason is wrong statement.


(iii) Assertion and reason both are correct statements and reason is correct explanation


for assertion.


(iv) Assertion and reason both are wrong statements.


 48

In the following questions a statement of Assertion (A) followed by a statement of reason

(R) is given. Choose the correct option out of the choices given below each question.


Assertion (A) : Electron gain enthalpy becomes less negative as we go down a group.


Reason (R) : Size of the atom increases on going down the group and the added electron would be farther from the nucleus.


(i) Assertion and reason both are correct statements but reason is not correct explanation for assertion.


(ii) Assertion and reason both are correct statements and reason is correct explanation for assertion.


(iii) Assertion and reason both are wrong statements.


(iv) Assertion is wrong statement but reason is correct statement.


 50

Define ionisation enthalpy. Discuss the factors affecting ionisation enthalpy of the elements and its trends in the periodic table.

 51

Justify the given statement with suitable examples— “the Properties of the elements are a periodic function of their atomic numbers”.