Friday
September 4, 2015

Homework Help: chemistry(water molecules)

Posted by alisha on Thursday, January 4, 2007 at 2:16pm.

What does a water molecule look like (the shape)and what atoms does it contain? Also why are water molecules polar molecules?

A water molecule contains two hydrogens and one oxygen between them. However, the 3 atoms are not in a straight line - the hydrogens are bent down kind of like this:

O
H H

Because the oxygen has a higher electronegativity than the hydrogens, it pulls a little harder on the electrons that are being shared. Because the 2 directions of the pull of oxygen on each bond don't cancel each other out, there is a dipole moment and the water molecule is polar. The definition of polar is that the difference between the electronegativites of the 2 atoms in question is between 0.6 and 2.

Sorry, the diagram didn't work out right:

(ignore the dots, I'm just using them so the computer will let me do this right)

...O...
H.....H

This helped me alot but if you are not too busy would you mind helping me with this question: List 2 physical properties of water that are determined by its structure and explain how the structure determines those properties.
I'm really confused because i don't quiet get the question.


  H
  ..
 :O:H
  ..


I hope that is a little better.

1)The boiling point is higher than normal because of the polarity of the water molecule. That allows hydrogen bonding to take place and the boiling point is raised over that expected.
2)The density of ice is smaller than liquid water (at the same temperature) because it occupies a larger volume when it freezes.

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