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Standard XII

Chemistry

Trend in Electron Affinity

The electron ...

Question

The electron affinity of sulphur is -200 kJ/mol. Then the electron affinity of oxygen is :

-142 kJ/mol

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-702 kJ/mol

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-332 kJ/mol

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-348 kJ/mol

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Solution

The correct option is A -142 kJ/mol
Due to small size and high electron density of oxygen compared to sulphur, interelectronic repulsion is higher in oxygen, resulting in less energy being released when an electron is added to oxygen, due to lesser stability after an electron is added, which is due to the interelectronic repulsion in the small oxygen atom. Hence, the electron affinity value of oxygen is lower than that of sulphur.

It is an exception to the normal trend of electron affinity in the periodic table.

Hence, the correct option is $A$

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Similar questions

Q. Electron affinity of chlorine is -348 kJ/mol. Then the electron affinity of fluorine is ........... in kJ/mol

Q. Use the following data to calculate second electron affinity of oxygen for the process

O^{-} (g) + e^{-} (g) \to O^{2 -} (g)

.
Heat of sublimation of

M g (s) = 147.7 k J / m o l

Ionisation energy of

M g (g)

to form

M g^{2 +} (g) = 2189 k J / m o l

Bond dissociation energy for

O_{2}

= 498.4 k J / m o l

First electron affinity of

O (g) = - 141 k J / m o l

Heat formation of

M g O (s) = - 601.7 k J / m o l

lattice energy of

M g O = - 3791 k J / m o l

Q. Use the following data to calculate the lattice energy of caesium oxide.
Enthalpy of formation of caesium oxide =

- 233 k J m o l^{- 1}

Enthalpy of sublimation of

C s = + 78 k J m o l^{- 1}

First ionization energy of

C s = + 375 k J m o l^{- 1}

Enthalpy of dissociation of

O_{2} (g) = 494 k J m o l^{- 1} o f O_{2} m o l e c u l e s

First electron affinity of

O = - 141 k J m o l^{- 1} o f O a t o m s

Second electron affinity of

O = + 845 k J m o l^{- 1} o f O^{1 -} i o n s

Q. Use the following data to calculate the lattice energy of caesium oxide.
Enthalpy of formation of caesium oxide

= - 233 kJ/mol

Enthalpy of sublimation of

C s = + 78 kJ/mol

First ionization energy of

C s = + 375 kJ/mol

Enthalpy of dissociation of

O_{2} (g) = 494 kJ/mol

First electron affinity of

O = - 141 kJ/mol

Second electron affinity of

O = + 845 kJ/mol

Q. Use the following data to calculate second electron affinity of oxygen for the process

O^{-} (g) + e^{-} (g) \to O^{2 -} (g)

.
Heat of sublimation of

M g (s) = 147.7 kJ/mol

Ionisation energy of

M g (g)

to form

M g^{2 +} (g) = 2189 kJ/mol

Bond dissociation energy for

O_{2}

= 498.4 kJ/mol

First electron affinity of

O (g) = - 141 kJ/mol

Heat formation of

M g O (s) = - 601.7 kJ/mol

lattice energy of

M g O = - 3791 kJ/mol

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