Question

Which would be a better nucleophile nitrogen or oxygen?

How can we explain the trend for what atoms would be better nucleiphile based on the periodic table?

Answer 1

N is a better nucleophile than O because lone pairs on O experience a higher nuclear attraction than those on N. As a result, the electrons are less available to attack.

Trends in decreasing nucleophilicity are to the right on a row and up on a column. (up because of the same concept, electrons are more polarizable when they experience a lower nuclear attraction, and thus are more available to attack, e.g. I is a better nucleophile than Br).

Answer 2

That's a Great and concise explanation!

So as we go across a period the increased nuclear charge makes the atom less able to donate it's electrons and thus less nucleophilc

I guess as we go down a group, and as the number of shells increases, shielding increases the likelihood that an element to donate it's electrons, so nucleiphile strength increases.