hydrogen bonds in water?

Question

How are water molecules able to make up to 4 hydrogen bonds with other molecules? I thought it would be 3 - the oxygen is attracted to another molecule's hydrogen, and each of the 2 hydrogens attracted to the oxygens of 2 other molecules. Can someone explain?
Also, on a website it said "The stronger the bonds, the more ordered and static is the resultant structure. The energetic cost of the disorder is proportional to the temperature, being smaller at lower temperatures." What does it mean by this? especially "energetic cost"
The site is http://www.lsbu.ac.uk/water/hbond-easy.html in case u need to see it in context.
I'd appreciate any help!

ok, so about oxygen's two pairs of electrons, does that mean that the hydrogen atoms of a water molecule essentially have no outer electrons (as they are 'inside', sharing electrons with oxygen) and thus need to gain 2, hence one pair of oxygen atoms for each hydrogen? Or is it nothing like this? I'm sorry if this doesn't make sense. I dont really get it. What happens to the electrons in hydrogen bonds? Or are electrons not involved, just opposite charges attracting...?

Answer 1

water molecules make up to 4 hydrogen bonds. Why? Water molecule is H2O. You may intuitively think the oxygen atom makes one bond, but if you look at its structure, it has two non-bonding pairs of electrons, or lone pairs coming off it. This enables two hydrogens from two different water molecules to attach to the lone electron pairs from the oxygen atom.

By energetic cost, I think it means that at higher temperatures the water has higher amounts of heat energy. And the higher the temperature, the weaker the hydrogen bonds are between water molecules, so the structure is not as ordered or static.

Answer 2

4 bonds because the O can hydrogen bond to 2 other H's (b/c the O has 2 lone pairs of electrons) and the 2 H's of the water can bond to 2 different O's on another molecule. thats kinda confusing, sorry.

the second part has to do with the concept of entropy. a higher temperature corresponds to a higher entropy (absolute zero theroretically has an entropy of 0). at lower temperatures, the entropy is lower and therefore it is easier for a compound to be more ordered b/c there are less possible ways for a molecule to exist (think of a dresser, with 5 drawers there are lots of places to put clothes and mess it up, but with 1 drawer, there is only one place to put clothes and only that 1 drawer can be messy; more drawers would correspond to a higher entropy [and temperature in this case]).

Answer 3

Gong Chan is absolutely correct, and you should award him full points for best answer. Another answer to your second question comes from *delta*H = *delta*E - T*delta*S, where T is the absolute temperature of the water and S is the entropy. The higher T gets, the higher T*delta*S gets. S is a measure of the disorder of water molecules.