Request a call back

Join NOW to get access to exclusive study material for best results

CBSE Class 11-science Answered

<div>Sir/mam&nbsp;</div> <div>&nbsp;</div> <div>Why is the electron gain enthalpy negative for alkali metals like Na, &nbsp;Li, K because they have big sizes and they do not tend to gain but to loose electrons and why do alkaline metals have +ve Electron gain enthalpy?<img src="https://images.topperlearning.com/topper/tinymce/imagemanager/files/8bae5edc439ad72026b7335ad9447c7957b1729e591c46.0790939514712469779041354463705.jpg" alt="" /></div>
Asked by Varsneya Srinivas | 15 Aug, 2016, 01:14: PM
Expert Answer
Electron gain enthalpy is the amount of energy released when an isolated gaseous atom accepts an electron to become a monovalent gaseous anion.  If an atom has spontaneous tendency, i.e., a positive tendency , to gain electron, then conventionally , its electron gain enthalpy is said to be negative and if the atom is reluctant to gain an electron, i.e., it has a negative tendency to gain an electron and is forced to accept it, its electron gain enthalpy is   positive. 

As a general rule, electron gain enthalpy becomes more negative with increase in atomic number across a period. The atomic size decreases and effective nuclear charge increases as we go from left to right across a period and consequently it will be easier to add an electron to smaller atom since the added electron on an average would be closer to the positively charged nucleus.

The trends in electron gain enthalpy values within a period are irregular for elements of group 2, group 15 and group 18 since they have atoms with symmetrical configuration (having filled and half-filled orbitals in the same sub-shell) and hence do not have any urge to take up extra electrons because their configuration will become unsymmetrical or less stable.

Answered by Arvind Diwale | 17 Aug, 2016, 11:51: AM

Concept Videos

CBSE 11-science - Chemistry
Asked by negimanish9735 | 28 Oct, 2020, 09:30: AM
ANSWERED BY EXPERT
CBSE 11-science - Chemistry
Asked by abhishhadnur | 28 Sep, 2020, 04:04: PM
ANSWERED BY EXPERT
CBSE 11-science - Chemistry
Asked by ingale.vishakha08 | 26 Jan, 2019, 02:27: PM
ANSWERED BY EXPERT
CBSE 11-science - Chemistry
Asked by Topperlearning User | 04 Jun, 2014, 01:23: PM
ANSWERED BY EXPERT
CBSE 11-science - Chemistry
Asked by Topperlearning User | 14 Aug, 2014, 01:24: PM
ANSWERED BY EXPERT
CBSE 11-science - Chemistry
Asked by Topperlearning User | 19 Apr, 2016, 12:30: PM
ANSWERED BY EXPERT
CBSE 11-science - Chemistry
Asked by Topperlearning User | 04 Jun, 2014, 01:23: PM
ANSWERED BY EXPERT
CBSE 11-science - Chemistry
Asked by Topperlearning User | 27 Jun, 2016, 01:02: PM
ANSWERED BY EXPERT
CBSE 11-science - Chemistry
Asked by Topperlearning User | 14 Aug, 2014, 01:15: PM
ANSWERED BY EXPERT
Season Break Offer!
Get 60% Flat off instantly.
Avail Now
×