Electron Affinity Trend    most atoms release energy when they gain an electron       this is defined to be a negative electron affinity     but some atoms require energy       this is defined to be a positive electron affinity energy is sometimes required due to:       1. opening a new sublevel       2. breaking a half-filled sublevel Example 1. Which atom would have a positive electron affinity, sodium or magnesium?       Na is 1s22s22p63s1 - the new electron would fill in the 3s orbital       Mg is 1s22s22p63s2 - the new electron would open the 3p sublevel       magnesium has a positive electron affinity --         it is difficult to open a new sublevel Example 2. Which atom would have a positive electron affinity, nitrogen or oxygen?       N is 1s22s22p3 - the new electron would enter the 3p sublevel       O is 1s22s22p4- the new electron would also enter the 3p sublevel       nitrogen has a positive electron affinity --         the p sublevel was half-filled with 3 electrons most atoms have negative electron affinities - they release energy some atoms predictably have positive electron affinities - they require energy      but there are NO CLEAR TRENDS

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