Which of these is correct? The hydrogen bond between two molecules of water is created because water is polar, non-polar, liquid, amphipathic or polyvalent?

Prison

The hydrogen bond between water molecules is created because water is a polar molecule. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/HydrogenBonds.html Jul 28 09, 6:04 PM

looney_tunes

There are other polar molecules, but not all of them form hydrogen bonds. Polar molecules occur because they have within them covalently-bonded atoms with dfifferent electronegativities, creating polar bonds. If the shape of the molecule means that these polar bonds do not interact so as to cancel each other out, the molecule will be polar. Polar molecules have a higher inter-molecular force of attraction than do non-polar molecules, as the oppositely-charged sites of the molecules attract each other. Hydrogen bonds form between molecules when one of the atoms involved in the polar bond is hydrogen - the hydrogen atom is often 'nearly ionised' within its covalent bond, so the amount of charge displacement is muchlarger than is the case for most polar bonds. Due to the shape of the water molecule, the oxygen atom acquires quite a (relatively) large excess negative sharge, while the region around the two hydrogen atoms has a significant deficiency. These parts of the two molecules attract each other with a stronger electric force than is usual for polar molecules. (Hydorgen bonds can also occur within larger molecules - it's part of what determines the structure of proteins, for example.) However, hydrogen bonding is only significant in solids and liquids, when the molecules are close enough to each other for the effect to be observed. http://en.wikipedia.org/wiki/Hydrogen_bond Jul 28 09, 7:29 PM

Watchkeeper

None of the alternatives given is correct. The hydrogen bond between two molecules of water is created because the high electronegativity of the oxygen atom causes the electrons in the O-H bond to be displaced towards the oxygen atom. This gives it a slight negative charge and at the same time gives the hydrogen atom a slight positive charge. The negatively-charged oxygen atom of one water molecule is then able to attract the positively-charged hydrogen atom of an adjacent water molecule (using the lone, i.e. non-bonding, electron pairs on the oxygen atom). This attraction is the hydrogen bond. In effect the hydrogen atom becomes a "bridge" between two oxygen atoms i.e. O-H----O. Note the linear arrangement of the 3 atoms concerned. Besides oxygen, only fluorine and nitrogen have sufficiently high electronegativities to form hydrogen bonds. Thus hydrogen fluoride and ammonia are also hydrogen bonded (F-H----F and N-H----N respectively). Hydrogen bonds are typically about 10% of the strength of an "average" covalent bond. http://www.chemguide.co.uk/atoms/bonding/hbond.html As looney_tunes points out, hydrogen bonding in proteins is essential in determining their structure, and also in the DNA double helix. http://www.chemguide.co.uk/organicprops/aminoacids/proteinstruct.html Jul 28 09, 10:55 PM