You are watching: Why does water have a higher boiling point than hf
DISCLAIMER: LONG ANSWER! Also really visual.
Hydrogen-bonding is the strongest intermolecular pressure in both #"HF"# and #"H"_2"O"#. Communication strength is dependence on communication distance, communication angle, and also the extensivity the the network.
When we attract out all the hydrogen-bonding interactions, and assume pure water and pure #"HF"#, we obtain (isolating a select set of molecules from an boundless matrix)#""^(<1>)##""^(<2>)#:
We can then take into consideration a few factors:Number of hydrogen-bonding donors and acceptors
Each water molecule can accept two hydrogen-bonding interaction (via the lone pairs) and donate two hydrogen-bonding interactions (via the hydrogens).
On the various other hand, every #"HF"# molecule accepts three hydrogen-bonding interactions (via the lone pairs) and also donates just one (via the hydrogen).
One might argue then the water has actually a more well balanced hydrogen-bonding network, which provides the mass system much less able to vaporize overall. This would support the higher boiling allude of water end #"HF"#.Electronegativities of #bb("F")# and #bb("O")#
#"F"# is much more electronegative, so the holds onto its electron density an ext easily; thus, the lone pairs space expected to be weaker donors the hydrogen-bonding interactions than the lone bag on #"O"#.
This would certainly seem to predict the each separation, personal, instance hydrogen-bonding interaction is weaker, which would assistance the higher boiling suggest of water end #"HF"#, BUT this is contradicted through the following point.Average raw hydrogen-bonding strengths in #bb("HF")# vs. Water
#"O"-"H"cdotcdotcdot:"O"-#, #DeltaH_("H"-"bond") ~~ "21 kJ/mol"#
#"F"-"H"cdotcdotcdot:"F"-#, #DeltaH_("H"-"bond") ~~ "161.5 kJ/mol"#
This data native Wikipedia argues that #"HF"# has actually stronger hydrogen-bonding interactions among #"HF"# molecules than in water.
This would not support the experimental proof that #"HF"# has actually a much lower boiling point, yet this additionally is simply a life number and does not consider, say, interaction angles in the bulk system.Observed hydrogen-bonding angles and also dimensions the interaction
#"HF"#, gift a linear molecule, has been seen to have actually zigzag hydrogen-bonding interactions, in two dimensions, with angles of #116^
#, since that would certainly give an ext direct dipole interactions. This borders the hydrogen-bonding strength of #"HF"#.
Water, gift a bending molecule v a tetrahedral electron geometry, deserve to hydrogen-bond in three dimensions.
Here"s an example of the tetrahedral cluster discovered in the local setting of a hydrogen-bonding interaction in water:
It may be that the extensivity of the hydrogen-bonding network, and also how it often tends to enhance the electron geometry the water, is what makes water"s boiling allude so high. This would support the higher boiling suggest of water end #"HF"#.
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Overall, these are the least-challenged determinants I can think of:Water deserve to make a more-balanced hydrogen-bonding network (two acceptors and two donors, instead of one donor and also three acceptors), making the mass system more uniformly interacting and thus more powerful as a whole.Water develops a an ext extensive hydrogen-bonding network (a three-dimensional tetrahedral regional environment, fairly than a two-dimensional zigzag environment), rendering the bulk system less easily vaporizable.Water generally has a more optimal edge of interaction, as it much more closely matches the electron geometry the the molecule and also aligns the interactions along the molecule dipole, whereas #"HF"# would have stronger hydrogen-bonding (in terms of raw numbers) if the interactions were linear.