Electron Affinity descripton.

[philip041]

I have been looking at websites on electron affinity. My notes report it as 'energy released when an atom gains an electron. Wikipedia http://en.wikipedia.org/wiki/Electron_affinity says the amount of energy released when detaching an electron from a singly charged negative ion,[1] i.e., the energy change for the process

X- → X + e−

This seems the reverse? Also on that same Wikipedia page it says you can't get negative elctron affinity values yet on good old hyperphysics http://hyperphysics.phy-astr.gsu.edu/Hbase/chemical/eleaff.html it uses a negative convention. I thought this was a modern site?

Can someone clear this up? Cheers!

 

[Gokul43201]

Physicists tend to use the opposite sign convention to chemists for EA. Chemists specify all EA values as positive.

See, for example:
http://www.webelements.com/periodicity/electron_affinity/
http://www.periodictable.com/Properties/A/ElectronAffinity.html

 

[charng]

I can confirm that the definition of electron affinity can be confusing and there are different conventions used to represent it. The basic concept of electron affinity is the energy change that occurs when an atom gains an electron to form a negatively charged ion. This can also be thought of as the energy released when an electron is added to a neutral atom to form a negative ion.

The confusion may arise from the notation used to represent this process. In the equation X- → X + e−, the X- represents a negatively charged ion, while X represents a neutral atom. When the electron is added to the neutral atom, it forms a negatively charged ion, releasing energy in the process. This is the convention used by Wikipedia.

However, the hyperphysics website uses a different convention where the X- represents a neutral atom and X represents a positively charged ion. In this case, the energy change would be positive when the atom gains an electron to form a neutral atom. This convention may seem counterintuitive, but it is still valid and used by some sources.

In summary, electron affinity is a measure of the energy change that occurs when an atom gains an electron. The notation used to represent this process may vary, but the concept remains the same. It is important to be aware of the different conventions used and to clarify which one is being used when discussing electron affinity.