Name: Variation of Atomic Radius in Periodic Table
Uploaded: 2019-07-19
Duration: 4 min 6 s
Description: The atomic radius is defined as the distance between the atom's nucleus and the outermost shell. But do you know how it varies in the periodic table? Let's find the answer in this video.

Question

Define electron gain enthalpy. Describe the factors which determine the magnitude and sign of electron gain enthalpy. What are the general trends of variation of electron gain enthalpies in the periodic table?

Accepted Answer

Electron gain enthalpy of an element may be defined as the energy released when a neutral isolated gaseous atom accepts an extra electron to form the gaseous negative ion, i.e., anion. It is denoted by $∆_{eg} H$ . In other words, the electron gain enthalpy of an element is a measure of the firmness or strength with which an extra electron is bound to it. Like ionisation enthalpy, electron gain enthalpy is measured either in electron volts per atom or $kJ {mol}^{- 1}$ .

Electron gain enthalpy ( $∆_{eg} H$ ) depends upon the following factors:

Atomic size: As the size of the atom increases, the distance between the nucleus and the outermost shell which receives the incoming electron increases. As a result, the force of attraction between the nucleus and the incoming electron decreases and hence the electron gain enthalpy becomes less negative.

Nuclear charge: As the nuclear charge increases, the force of attraction between the nucleus and the incoming electron increases and hence the electron gain enthalpy becomes more negative.

Electronic configuration: Elements or species having stable electronic configuration (i.e., half-filled, fully-filled or noble gas configuration) require large amount of energy to add an electron so, the electron gain enthalpies have large positive values.

Variation in Groups: On moving down the group, the size of the atom increases drastically, therefore, the influence of nucleus on the outermost electrons becomes less, hence, the electron gain enthalpy also becomes less negative.
Variation in Periods: On moving from left to right in a period, the size of the atom decreases therefore, the influence of nucleus on the outermost electrons increases, thus, the incoming electron experiences more attraction from the nucleus and hence, the electron gain enthalpy becomes more negative.

Define electron gain enthalpy. Describe the factors which determine the magnitude and sign of electron gain enthalpy. What are the general trends of variation of electron gain enthalpies in the periodic table?

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