Question

How to determine direction of polarity?
For instance im studying from a practice quiz, an it says that in

CH3OH

the oxygen is slightly negative, which is understandable as its next to F. but then it says the H is slightly positive. why the H and not the carbon which is two spaces away from oxygen? is it because H is MUCH further away?

Answer 1

All of this is relative to F which has been set arbitrarily at 4.0. Look up the electronegativity (EN). EN for F is 4.0, O is 3.0, H is 2.1, C is 2.4. So what it is saying is that the O (at 3.0) attracts electrons to it better than the H to the right of it (at 2.1) so the O is slightly negativity. So if you attract the electrons a little closer to O than H, that makes O a little negative and H a little positive.
Examples: I can't make spaces on this forum so let s stand for space.
H:F in real life looks more like Hsss:F so the F has a few more electrons and the H has a few less so H has a slight + charge and the F has a slight - charge. Same thing with OH^- which would be -O:H but really like -OssH. Again, the O attracts the electrons more strongly than H therefore the O has a slight - charge and the H a slight + charge. The difference is more pronounced in HF than in OH.