Help in Chemistry (bonding)

• Bigcable22

  19 May 08, 20:25

  why are the covalent bonds in ice stronger than in water vapour?

  i googled already no direct good answer..pls help!

• secretliker

  20 May 08, 00:35

  These may help.
  http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/HydrogenBonds.html
  http://en.wikipedia.org/wiki/Ice

  If 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?

• UltimaOnline

  20 May 08, 12:01

  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).
• SBS n SMRT

  20 May 08, 16:01

  if you have GCE O level Chemistry matters textbook, you could also refer to the science today part where it is barly addressed