Chapter 3: Classification of Elements and Periodicity in Properties

Q49Written answer

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

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Ans: The factors that affects electron gain enthalpy are as follows:

(a) Effective nuclear charge with its increase the electron gain enthalpy also increases

(b) Atomic size with its increase the electron gain enthalpy decreases

(c) The e--e- repulsion with its increase the electron gain enthalpy decreases

(d) Whenever there exists half filled or completely filled orbital than it lead to decrease the electron gain enthalpy because it leads to give extra stability to the atom due to symmetry.

The electron gain enthalpy decreases down the group and increases across the period.

Q50Written answer

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

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Ans: The amount of energy required to remove an electron from the outermost shell of an isolated gaseous atom in its ground state is said to be ionisation enthalpy.

The factors that affect ionization enthalpy of the elements are as follows:

a. Effective nuclear charge with its increase the ionization enthalpy also increases

b. Atomic size with its increase the ionization enthalpy decreases

c. The e--e- repulsion with its increase the ionization enthalpy decreases

d. Whenever there exists half filled or completely filled orbital than it lead to increase the ionization enthalpy because it leads to give extra stability to the atom due to symmetry

The ionization enthalpy decreases down the group and increases across the period.

Q51Written answer

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

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Ans: The chemical properties and physical properties of the elements depends upon its outer electron configuration which ultimately is the periodic function of the atomic number. The elements which possess the same outer electron configuration belong to the same group or family showing similar properties.

Q52Written answer

Write down the outermost electronic configuration of alkali metals. How will you justify their placement in group 1 of the periodic table?

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Ans: The group 1 elements are called alkali metals which possess outermost electronic configuration as ns1.All the elements that have same outermost electron configuration possess similar properties and are placed in the same group.

Atomic Number	Symbol	Electronic Configuration
3	Li	\[\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{1}}}\text{ }\left( \text{or} \right)\text{ }\left[ \text{He} \right]\text{ 2}{{\text{s}}^{\text{1}}}\]
11	Na	\[\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{\text{2}}}\text{ }\left( \text{or} \right)\text{ }\left[ \text{Ne} \right]\text{3}{{\text{s}}^{\text{1}}}\]
19	K	\[\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{\text{2}}}\text{4}{{\text{s}}^{\text{1}}}\left( \text{or} \right)\text{ }\left[ \text{Ar} \right]\text{4}{{\text{s}}^{\text{1}}}\]
37	Rb	\[\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{\text{2}}}\text{3}{{\text{d}}^{\text{10}}}\text{4}{{\text{s}}^{\text{2}}}\text{4}{{\text{p}}^{\text{6}}}\text{5}{{\text{s}}^{\text{1}}}\left( \text{or} \right)\left[ \text{Kr} \right]\text{5}{{\text{s}}^{\text{1}}}\]
55 87	Cs Fr	\[\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{\text{2}}}\text{3}{{\text{p}}^{\text{6}}}\text{3}{{\text{d}}^{\text{10}}}\text{4}{{\text{s}}^{\text{2}}}\text{4}{{\text{p}}^{\text{6}}}\text{5}{{\text{d}}^{\text{10}}}\text{5}{{\text{s}}^{\text{2}}}\text{5}{{\text{p}}^{\text{6}}}\text{6}{{\text{s}}^{\text{1}}}\left( \text{or} \right)\left[ \text{Xe} \right]\text{6}{{\text{s}}^{\text{1}}}\left[ \text{Rn} \right]\text{7}{{\text{s}}^{\text{1}}}\]

Q53Written answer

Write the drawbacks in Mendeleev’s periodic table that led to its modification.

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Ans: Mendeleev arranged the elements as the periodicity of their atomic weights.

The drawbacks of Mendeleev’s periodic table are as follows:-

a. The position of hydrogen in the periodic table is not specified

b. Isotopes are not included in the periodic table

c. Elements with higher atomic mass are placed before the elements with lower atomic mass. For e.g- Co & Ni

d. Gaps are left in his table considering the fact that more elements are yet to be discovered

e. Inappropriate position of group VII

Q54Written answer

In what manner is the long form of periodic table better than Mendeleev’s periodic table? Explain with examples

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Ans: The following points make long form of periodic table better than Mendeleev’s periodic table :-

a. It is a periodic function of atomic number

b. Elements are grouped as per there outermost electronic configuration

c. Proper segregation of metals and non-metals

d. More appropriate position of group VII

Q55Written answer

Discuss and compare the trend in ionisation enthalpy of the elements of group1 with those of group17 elements

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Ans: As we move across the periodic table the ionization energy increases because of the increase in the effective nuclear charge and decrease of the shielding effect as more and more electrons get added in the same orbital. Thus group 1 has lower ionization enthalpy compared to that of group 17 and also group 1 by losing one electron it will acquire the nearest noble gas electronic configuration which also contributes towards its lower ionization enthalpy.

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