Posted: Tue Oct 24, 2017 9:39 pm
In which scenario would there be a negative/positive electron affinity? I just can't visualize why there needs to be more energy /release of energy when attaching an electron to an atom.
Re: Electron Affinity
Posted: Wed Oct 25, 2017 9:55 am
So electron affinity is the energy released when an electron is added to an atom in the gas phase.
A positive election affinity means that energy is released when an electron attaches to an atom, and this occurs if the atom has many electrons in its valence shell and thus prefers to gain electrons in order to complete its valence shell. So, for atoms of elements in groups 16 and 17, energy is released when an electron is added - and the electron affinity is positive - because the electron is filling the valence shell and
A negative electron affinity means that energy must be supplied to push an electron onto an atom, and this occurs if the atom has less electrons in its valence shell. Since there are only a few I the valence shell, it is easier for the atom to lose those electron than gain them in order to end up with a complete valence shell. Thus, energy must be supplied to the atom in order to force additional electrons to join the valence shell.
It is also important to keep in mind that second electron affinities tend to be lower/more negative because the first addition of an electron to an atom has increased the electron repulsion, and thus, makes it harder to add another electron to the atom.
I hope this clarifies things a bit!