Electonegativity/Polarity?

Question

When finding the type of bond a compound has, polar or nonpolar and covalent or noncovalent, I know I have to subtract the electronegativity numbers of each and use the scale to decide. My question is-suppose it is water - H2O. Hydrogen has an electronegativity of 2.1 and oxygen is 3.5, should I multiply the 2.1 of H by 2 because there are 2 H atoms? so 2.1 x 2 = 4.2 and subtract 4.2 - 3.5 = 0.7. Or do I just need 1 H in the equation?
I am a 44 yrs old woman, gone back to college and I don't remember any of this stuff.
Thanks.

Answer 1

I respect your decision to go back to college. I know how tough that is, having done the same thing myself . . . and succeeded. So, hang in there!

To answer your question: No, you would not add them together. The reason is, you are finding type of bond in a compound, you do it for each bond individually. In water BOTH bonds are polar. You can use the electronegativity numbers and scale to do this, but do it individually for each bond in a compound. Since water has two H-O bonds, both of these bonds are polar.

Let me give you a little assistance in the logic of bonds on a more simplified level. This is how I explain polar and non-polar covalent bonds to my chemistry students.

The only true non-polar covalent bonds are those that form between atoms that are alike, such as in H2, O2, N2, etc. The polarity of a bond is the result of the "pull" on electrons by protons. An atom that has more protons will have a greater pull on any of the electrons in a covalent bond. It's kind of like a game of tug-of-war. Elements that are very close together in the periodic table, such as carbon and nitrogen, will make a slightly polar bond because they differ in the number of protons, but not by much. Elements that are farther apart from each other in the periodic table will make more polar bonds. Elements in Groups 1 and 2 when joining with elements in Group 17 will ALWAYS make ionic bonds. I hope this helps.

BEEN THERE AND DONE THAT AT 37

CHEMISTRY TEACHER