[P-man]

OK so water is a polar molecule. The oxygen has a stronger hold on the electrons than hydrogen does so therefore the oxygen is slightly negative and the hydrogen is slightly positive. I have a few questions about this (sorry my question mark key is broken so I used three dots instead).

How did they find out that the oxygen is slightly negative etc. Or is it just a hypothetical statement...

Do all polar molecules have a slightly positive part and a slightly negative part...

Does the oxygen have a stronger hold on the electrons because it has a larger nucleus (more protons)...

I know I may sound stupid but I'm trying to understand what my ******* science teacher won't explain.

[enahs]

How did they find out that the oxygen is slightly negative etc. Or is it just a hypothetical statement...

That is a complicated question and can be answered on so many ways. Yes it can be shown hypothetically. It can be shown through measurements. Take more chemistry to learn, as I doubt anybody wants to type out a full answer to that! heh

Do all polar molecules have a slightly positive part and a slightly negative part...

Yep.

Does the oxygen have a stronger hold on the electrons because it has a larger nucleus (more protons)...

Oxygen is more electronegative then Hydrogen. The amount of protons does play a role, but so do many other things.

This page might help you with all your questions in general:
http://www.chemguide.co.uk/atoms/bonding/electroneg.html

[Mitch]

Oxygen isn't more negative than anything else if it existed isolated in a vacuum not bonded to anything. If it was bonded to something like Hydrogen, than you could make a relationship that since Oxygen has more protons it will pull more of the electron density towards it. We like to use concepts like effective nuclear charge and other such esoteric proper nouns, but I think you have a good chemical sense of what is causing it and their natural relationships.