Quantum Mechanics

[CrystalBruin3C]

Having trouble with this homework problem.

2.67 Which element of each of the following pairs has the higher electron affinity: (a) oxygen or fluorine; (b) nitrogen or carbon; (c) chlorine or bromine; (d) lithium or sodium?

[Kyra Dingle 1B]

I believe to determine which has a higher electron affinity, you would need to refer to the periodic table. Electron affinities tend to be the highest towards the right of the periodic table. You would apply this electron affinity trend by comparing where each element is locating in relation to each other. For example, for the first pair, oxygen and fluorine, fluorine would have the higher electron affinity as it is located to the right of oxygen.

[Isaiah Little 1A 14B]

Generally speaking, electron affinity increases up a group and across a period. This is mainly due to the shielding of electrons and an electron's "desire" to achieve noble gas configuration. For instance, fluorine has a higher electron affinity than oxygen because the former only needs one electron to achieve [Ne], whereas oxygen requires two; therefore, fluorine has a stronger pull on available electrons for bonding. Electron affinity decreases down a group because of shielding, where more layers/shells of electrons damper the attractive pull of an atom's positively-charged nucleus on negatively-charged elecrons.

[Jason Muljadi 2C]

Why is it that carbon has a higher affinity than nitrogen when nitrogen is at the right of the carbon? I thought that as you go more right, there is a higher electron affinity. What is the exception with carbon that makes it have a higher electron affinity?

[Erik Khong 2E]

Why is it that carbon has a higher affinity than nitrogen when nitrogen is at the right of the carbon? I thought that as you go more right, there is a higher electron affinity. What is the exception with carbon that makes it have a higher electron affinity?

Carbon has a higher electronic affinity than Nitrogen because Nitrogen already has 3 single electrons in its three orbitals (2s2 2p3). Adding a fourth electron to one of the orbitals will be harder because it will lose its stable configuration. It's easier to add another electron to Oxygen because it already has an orbital with a pair, so it isn't as repulsive. (2s2 2p4)