what makes water molecule polar?

Question

i read the text, but didn't understand a thing...if possible please explain a little so a dummy like me can understand..... thnk u =]

Answer 1

the asymmetrical shape it has. water is H2O but it is bent at an angle and it is not a linear molecule like CO2.

This is the shape of a water molecule which is asymmetrical because the two hydrogen molecules are not equally pulling on the oxygen model. Each hydrogen molecule is pulling at an angle.

http://www.marietta.edu/~mcshaffd/aquatic/sextant/physmol.gif

As for carbon dioxide it contains a linear shape and therefore is symmetrical. Where as the oxygen molecules are equally pulling on each side of the carbon molecule:

http://library.thinkquest.org/11226/image/co2.jpg

Answer 2

Let's say for a moment that the hydrogen atoms bonded with the oxygen atom at 180 degrees apart from one another. The molecule would be non-polar because the electron cloud would be equally distributed on all sides. No slight positive or negative anywhere, just a balanced cloud of electrons in all direction, in the outer shell of the molecule.

But that is a physically unstable condition. It wouldn't much of any external energy to knock one of the hydrogen atoms out of that alignment

It's kind of like balancing a tennis ball on top of a bowling ball
The hydrogen atoms are like the tennis ball, one small 'puff' of wind (another molecule passing by) and it goes out of balance.

Well, the place where the 2 hydrogen atoms are balanced but can't be 'tipped over' is at about 105 degrees. Any closer than ~105 degrees and the hydrogen 'like' charges would repel each other, any further away and you get the tennis-ball balancing-on-the-bowling-ball effect.

The specific physics of how it is this particular angle (105) is probably 'beyond' your textbook.

Since there are 2 hydrogen atoms on one side and oxygen on the other, that exposes the electron cloud so that the bulk of the negative charge falls toward the fat oxygen atom (they congregate over on that side), while leaving a lack of electron charge on the hydrogen side. The O side becomes slightly negative, while the H side is slightly positive.

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Answer 3

Because of electronegativity. Oxygen atoms are strong electronegative atoms. I believe the only atom more electronegative is Florine.

Electronegative atoms are bullies. They hog electrons. In water, Oxygen pulls the electrons away from Hydrogen as much as it can. A polar molecule means that there is a greater charge on one side of the molecule than the other. In this case, there is a greater negative charge on the Oxygen.

So - lets think of it like this: Oxygen is a kid clinging to a bunch of toys trying to keep them away from two other, smaller Hydrogen kids. The little kids keep coming up behind him and trying to snatch the toys from under his elbow, but the bigger kid turns away and holds on tight so they can't get any toys. There is a greater concentration of toys in the big kid's arms than the little kids' arms.

So - just as a bully makes sure that toys are not distributed evenly, an electronegative atom makes sure electrons are not distributed evenly.

I hope that analogy works for you.

Answer 4

Oxygen is a more electronegative molecule that both of the hydrogens that are attached.