Question

Why are certain atoms more electronegative than others? For example, what is it about oxygen that makes it more electronegative then the elements to its left on the periodic table?

Answer 1

the electronegativity is defined by the pursuit of an element to achieve noble gas configuration with its electrons.

there are a variety of conditions that play into that:
first, there is the proximity of given element to the desired state. the halogens only need to aquire one more electron, rendering their electronegativity very high. alkaline metals like sodium need to give one electron away, so this happens for free (very low electronegativity).

then, there is the size of the atom. size goes along with greater stabilizing potential of the non-ionic state. thus, the further you go downwards in a main group, you will see a decrease in electronegativities.

for subgroup elements, there are some complex mechanisms going on with their d- and f-orbitals, so the interesting part is over now. hope that helps. :)

Answer 2

My reply got erased! Yes this definitely helps, thank you. I thought it might have something to do with having more protons to attract the electrons, but this didn't make sense because there are weak electronegative elements that have more protons than strong electronegative elements, when you go down to the next row.

Answer 3

It is defined as the ability of an element in a bond to attract the shared pair of electrons towards itself. So when you have C-Cl bond, where is the electron pair? Because Cl has a greater power to pull the electron pair towards itself, it is called more electronegative of the two. You can look up the electronegativities of all atoms in the periodic table. F is the most electronegative element.