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Can someone explain why electron affinity is the highest in the top right corner of the periodic table. I understand it is the energy released when an electron is added, but why is that highest in the top right corner?
The elements in the top right easily accept electrons due to them having the tendency to become more stable (8e-). So if fluorine has 7e- it would easily accept an additional e- bc having 8e- would make it more stable. Whereas elements like Na+ would have a lower electron affinity because adding an electron would cause it to be more unstable.
I like to think of electron affinity as how much an atom wants an e-. So, when you move to the right on the PT, you are getting elements with almost full shells. They really want to complete the octet rule so they are stable, thus they really want the e-, especially because on the very right, like fluorine and chlorine, they only need 1 more e- to fill their shell. Moving up on the PT, you are getting smaller atoms, so the pull of the positively charged nucleus is stronger and that attraction for pulling in an e- is higher. Thus, you must follow both these trends which takes you all the way up and right, making the top right the highest electron affinity.
Electron affinity is highest in the top right corner of the PT since these elements have shells that are nearly full, so they need less electrons to complete an octet versus elements towards the bottom left corner of the PT. For example, fluorine has 7 valence electrons and only needs one more electron to complete its octet, so it has a high electron affinity.
The elements in the top right of the periodic table have shells that are nearly full, meaning they need few electrons to complete an octet, whereas elements in the bottom left corner of the periodic table need to gain far more electrons in order to have an octet.
Elements on both sides of the periodic table are essentially trying to get "closer to" a noble gas in terms of stability in its electrons. Because elements on the left side want to lose electrons in order to be more stable, they would have less of an affinity, or attraction to, other electrons.
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