Why Does Electron Affinity Have Different Values and Conventions?

[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