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4 posts
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These may help.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/HydrogenBonds.html
http://en.wikipedia.org/wiki/IceIf I'm not wrong, between molecules of water in gaseous state, the forces which held them together are Van der Waals' forces of attraction. The molecules are moving randomly and are far apart. When they lose energy, the molecules become more closely packed together with hydrogen bonds forming between the polar ends of the water molecules?
Edited by secretliker 20 May `08, 12:36AM
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Moderator'A' & 'O' Levels Chemistry & Biology Ex-MOE Teacher Tutor
840 posts since May '05-
Secretliker is about right, except that in the gaseous state, there are negligible forces ‘holding them together’, as they’re not together at all (by virtue of being in the gaseous state).
To answer Bigcable22’s question, the covalent bonds in ice are NOT stronger than in water vapour (because by covalent bonds, you mean the polar covalent bonds between H and O in a single water molecule – no reason for the bond enthalpy of these bonds to change).
Rather, ice is a hard solid, compared to the soft gas of water vapour, because in the solid state of ice, water has formed a macromolecular solid, macham like diamond, with a similar tetrahedral geometry arrangement or lattice structure. The 4 bonds between each water molecule (visualize the 4 bonds between carbonds in diamond), are not covalent bonds, as pointed out by secretliker, but are hydrogen bonds between the partial positive Hs and the (lone pairs of the) partial negative Os.
It is the remarkable similarity in bond angles (allowed by a remarkable similarity in bond lengths, as well as the molecular geometry of the water molecule) that allows water to form a giant tetrahedral (macromolecular) solid that gives ice its hardness, and its openness (ie. compared to liquid water, solid ice occupies more space, hence have lower density and can float on liquid water).
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