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Electron Gain Enthalpy - Practice Questions & MCQ

Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET

Quick Facts

  • Electron Gain Enthalpy or Electron Affinity is considered one the most difficult concept.

  • 25 Questions around this concept.

Solve by difficulty

Which among the following factors is the most important in making fluorine the strongest oxidising agent?

In which of the following options, the order of arrangement does not agree with the variation of property indicated against it?

The formation of the oxide ion O2-(g), from oxygen atom requires first an exothermic and then an endothermic step as shown below: 

O(g)+e^{-}\rightarrow O^{-}(g); \Delta_{f}H^{\ominus}=-141kJ\:\:mol^{-1}

O^{-}(g)+e^{-}\rightarrow O^{2-}(g); \Delta_{f}H^{\ominus}=+780kJ\:\:mol^{-1}

Thus process of formation of O^{2-}  in gas phase is unfavourable even though O^{2-}  is isoelectronic with neon. It is due to the fact that

Which of the following arrangements represents the correct order of least negative to most negative electron gain enthalpy for C, Ca, Al, F, O?

Which of the following represents the correct order of increasing electron gain enthalpy with negative sign for the elements O, S, F and Cl

Concepts Covered - 1

Electron Gain Enthalpy or Electron Affinity

Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to a neutral atom to form a negative ion. It is also known as electron gain enthalpy.

A(g) + e →A-(g) + ?egH

 

Factors affecting electron affinity

The electron gain enthalpy or electron affinity depends upon various factors such as:

  • Atomic Size

With the increase of atomic size, the distance between the nucleus and the last shell electrons also increases due to which the force of attraction between the nucleus and the incoming electron decreases. Hence, the electron gain enthalpy becomes less negative.

  • Nuclear Charge

With the increase of nuclear charge, the force of attraction between the nucleus and the incoming electron increases. Thus, the electron gain enthalpy becomes more negative.

  • Electronic Configuration

Elements that have half filled or completely filled orbitals are more stable than others. I these cases, energy has to be provided to add an electron. Thus, their electron gain enthalpy has large positive values. 

 

Variation of Electron Affinity

  • The electron gain enthalpy becomes less negative in going from top to bottom in a group.

  • In moving from top to bottom in a group, both the atomic size and the nuclear charge increases. But the effect of the increase in atomic size is more prevalent than the nuclear charge.

  • With the increase in atomic size, the attraction of the nucleus for the incoming electron decreases. Hence, the electron gain enthalpy becomes less negative. But in moving from left to right in a period, the attraction of the nucleus and the incoming electron increases and thus electron gain enthalpy becomes more negative.

  • Halogens have the most negative electron gain enthalpies. In moving down from chlorine to iodine, the electron gain enthalpies become less negative due to the increase in their atomic radii.

  • Chlorine has the most negative electron gain enthalpy value than fluorine. Because fluorine is very small in size due to which there is a very strong inter-electronic repulsion for the incoming electron, thus its electron gain enthalpy is less than chlorine.

Importance of Electron Gain Enthalpy

Some properties of the elements can be predicted on the basis of the electron gain enthalpy values.

  • The elements with high electron gain enthalpy values accept electrons easily and form ionic compounds. For example NaCl.

  • The elements with high electron gain enthalpy values are strong oxidising agents. For example, F, Cl, O.

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Electron Gain Enthalpy or Electron Affinity

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Electron Gain Enthalpy or Electron Affinity

Chemistry Part I Textbook for Class XI

Page No. : 90

Line : 60

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