Quarter+2+Applying+past+knowledge+to+new+situations

5. Based on electronegativity values, which bond is the most polar? A. H-C B. O-F C. N-O D. C-O
 * Element || Electronegativity ||
 * H || 2.1 ||
 * C || 2.5 ||
 * N || 3.0 ||
 * O || 3.5 ||
 * F || 4.0 ||

The question above was on the bonding test which also showed up on the exam. On the test i got it right because i did the review that was given and looked it up online. The answer is D. On the exam though i had completely forgotten about it, although it was just simple math but there was no chart stating the electronegativity so i started to panic. The first idea i thought of was drawing each covalent bond out to see the electrons that weren't matched... i immediately realized that was impossible and would take too much time. I changed an idea and thought about periodic trends. As one moves left to right across a period electronegativity increases due to the stronger attraction the atoms obtain as the nuclear charge increases. And as one moves down a group, electronegativity decreases due to the longer distance between the nucleus and the valence electron shell. Hydrogen and carbon occured to me the furthest apart, the elements are in different groups too so shouldn't H-C be more electronegative? Then i remembered that hydrogen has a high electron affinity itself and probably won't be detached easily. So i left out the choice A and guessed the answer D because C and O were furthest apart so it would probably be the most electronegative. Overall, i think it was quite some luck but i still tried to think about what i learned before.