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Answer to Question #53277 in Inorganic Chemistry for manisha

Question #53277
explain electron gain enthalpy in brief with the help of examples?also explain its trend in period and group .
Expert's answer
Electron gain enthalpy is the energy which forms upon addition one electron to an atom in gas phase.
F + 1e → F- + ∆H = -328 kJ/mol
He + 1e → He- + ∆H = +48 kJ/mol
For groups, its value increases upon the increase in atomic number because increase in the radius of element makes weaker an interaction between a nucleus and added electron. It is known that the radius increases from the top to the down in the group.
For periods, electron gain enthalpy decreases from the first to the seventh group, which is also associated with the increase of the atomic radii. However, the enthalpy curve passes through the maxima at the second, the fifth and the eighth groups, which have the stable ns2, ns2np3 and ns2np6 electron configurations, respectively.

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Assignment Expert
21.07.15, 14:15

Dear manisha,
An increase in atomic radii is linked to an increase (more positive) electron gain enthalpy. Electron gain enthalpy becomes more negative (decreases) with increase in atomic number (decrease of atomic radii) across a period. It is easier to add an electron to smaller atom as it is closer to the atomic nuclei.

19.07.15, 08:50

experts , can you please explain me the exact explaination for decrease in enthalpy in period , as you said it also linked with increase in atomic radii. but atomic radii decrease in period so it linked with the increase in atomic radii.

Assignment Expert
09.07.15, 10:02

Dear manisha,
The stronger is interaction between atom and electron the more energy is released. The value of enthalpy is negative ("-") due to the loss of
energy. So, more negative value means more energy released. The value of enthalpy (i.e. group) becomes less negative or even positive
("+"). It means that enthalpy (in group or period) is changed from negative to positive values. So, mathematically its value increases (from "-" to "+") though the absolute amount of released energy decreases. 

08.07.15, 20:17

thankyou for good answer but i did not get the excat reason that why it increase in group ,as atomic size increases down the group so interaction between nucleus and atom become weaker than ....what happened i can't understand.....so please explain me again.

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