He Consider the electron affinities for the p-block elements in Figure 6.18 Note

Question

He Consider the electron affinities for the p-block elements in Figure 6.18 Note that the magnitude of electron affinity tends to increase from left to right, meaning that more energy is released when an electron is added to the atom. However, the elements in Group SA (15) do not follow this trend. They have electron affinities that are smaller in magnitude than the preceding element. In fact, nitrogen does not have a measurable electron affinity at all. How do you account for this observation? 10 Ne BCNO Al Si P S CAr Ga Ge As Se In Sn Sb Te Xe TI Pb Bi Po At Rn Kr 51 81 b Why do the elements in Group SA (15) that are heavier than nitrogen have a measurable electron affinity, but nitrogen does not? RE 6.18 Electron affinities (in ev) for the p-block elements c Another general trend in electron affinity is that its magnitude decreases (less energy is released when arn electron is added) from top to bottom down a group. However, Periods 2 and 3 do not follow this trend. The electron affinities for the Period 3 atoms in the p-block all have a greater magnitude then their groupmates in Period 2. How do you account for the fact that it is more energetically favorable to add an electron toa Period 3 atom than it is to add an electron to the analogous Period 2 atom?

Explanation / Answer

The electrons are paired in one of the most "stable" forms

for instance

"p" block is only 50% filled, for each one of them

px, py,pz will have only 1 electron each, according to Hund rule

Recall that the Nitrogen family has only 3 electrons in its valence shell, they ar equally distributed

Therefore, from all broups, B,C,O,F this is the only exception, mainly because of this array of electrons

b)

Nitrogen is very small, therefore, the proton / electron ratio/distance is almost "pure" or easier to predict.

The 50% filled orbitals are directly related to the nucleus, there are no "other p-orbital" electrons

note that

P,As,Sb... will have "p.orbitals" in their core electronic configuration, therefore this is "array" can't be related directly

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