Is this a good alternative definition of electron affinity?

  • #1
Summary:
electron affinity (traditional definition): the amount of energy released by an element in its gas form when gaining an electron

second definition?: the stability gained by an element in its gas form when gaining an electron

Is this a correct definition?
traditional definition of electron affinity: the amount of energy released by an element in its gas form when gaining an electron

second definition?: the stability gained by an element in its gas form when gaining an electron (e.g. halogens are more stable after gaining an electron, and when gaining an electron, the system [i.e. electron + atom] loses energy, thus becoming more stable)

reasoning: losing energy is highly associated with gaining stability (I think they are two sides of the same thermodynamic concept)

Is this an acceptable alternative definition? From a distance it looks okay, but I am often wrong about such things.
 

Answers and Replies

  • #2
etotheipi
I'm by no means an authority, however I wouldn't say the second definition is sufficient.

The electron affinity, ##E_{ea}##, is a numerical quantity - the energy released per mole on gaining an electron. As such, the definition must be precise.

Granted, the atom-electron system becomes more energetically stable after the first electron affinity. But this is more of a consequence, and not the definition of ##E_{ea}##.

As an aside, it might be worthwhile to make the distinction between ##E_{ea}## and the enthalpy change of electron capture ionisation. ##E_{ea}## is the energy released, whilst the enthalpy change is a change in the total energy. Assuming constant pressure and volume, ##\Delta H_{ea} = - E_{ea}##.
 
  • Like
Likes sneakycooky
  • #3
I'm by no means an authority, however I wouldn't say the second definition is sufficient.

The electron affinity, ##E_{ea}##, is a numerical quantity - the energy released per mole on gaining an electron. As such, the definition must be precise.

Granted, the atom-electron system becomes more energetically stable after the first electron affinity. But this is more of a consequence, and not the definition of ##E_{ea}##.

As an aside, it might be worthwhile to make the distinction between ##E_{ea}## and the enthalpy change of electron capture ionisation. ##E_{ea}## is the energy released, whilst the enthalpy change is a change in the total energy. Assuming constant pressure and volume, ##\Delta H_{ea} = - E_{ea}##.
Interesting. I think I agree with you; the trend of increasing the system's stability upon gaining an electron does exist, but it is much more difficult to measure; the more precise measurement makes for a better definition. I am glad that the trend actually exists, as it does help my understanding of the concept.
Thanks for your input!
 
  • #4
mjc123
Science Advisor
Homework Helper
1,176
613
First, to be pedantic, the electron affinity refers to an atom of the element. E.g. the electron affinity of chlorine relates to the reaction Cl(g) + e → Cl-(g). Talking of "an element in its gas form" might suggest the participation of Cl2(g).

Second, "stability" is a woolly concept, by no means equivalent to the negative of energy. You always have to ask: stability with respect to what?
For instance, the second electron affinity of oxygen is negative; that is, O2- is unstable relative to O- + e in the gas phase. Yet we can form many oxides, containing the O2- ion and not O-. This is because the extra energy put in to create O2- is more than compensated for by the lattice energy of the ionic solid containing O2-, so the overall process is favourable.
 
  • Like
  • Informative
Likes jim mcnamara, sneakycooky and etotheipi

Related Threads on Is this a good alternative definition of electron affinity?

  • Last Post
Replies
2
Views
3K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
5
Views
8K
  • Last Post
Replies
1
Views
2K
Replies
3
Views
2K
Replies
1
Views
708
Replies
5
Views
9K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
7
Views
2K
  • Last Post
Replies
4
Views
3K
Top