chem!!!--hydrogen bond

Steps to predict the number of hydrogen bonds for each molecule.
(1) Count the number of lone pairs which can form hydrogen bond(s).
(2) Count the number of H atoms which can form hydrogen bonds(s).
(3) Number of hydrogen bonds = Smaller number in (1) and (2)

1. H-F
(1) In each molecule, there is 1 H atom which can form hydrogen bond.
(2) In each molecule, the 3 lone pairs on the F atom can form hydrogen bonds.
(3) Each HF molecule can form 1hydrogen bond.
......H-F......
In the above diagram, there are two dotted lines to represent hydrogen bonds.However, each molecule can only form one hydrogen bond. This is because eachdotted line is shared by 2 molecules, but is NOT belonged to one singlemolecule.

2. H2O
(1) In each molecule, there are 2 H atoms which can form hydrogen bonds.
(2) In each molecule, the 2 lone pairs on the O atom can form hydrogen bonds.
(3) Each H2O molecule can form 2hydrogen bonds.

3. NH3
(1) In each molecule, there are 3 H atoms which can form hydrogen bond.
(2) In each molecule, the lone pair on the N atom can form hydrogen bond.
(3) Each NH3 molecule can form 1hydrogen bond.

4. methanol - CH3OH
(1) In each molecule, there are 1 H atom which can form hydrogen bond, althoughthere are 4 H atoms.
(2) In each molecule, the lone pair on the O atom can form hydrogen bond.
(3) Each CH3OH molecule can form 1 hydrogen bond.

2012-09-05 22:25:39 補充：
This is because the book is wrong.

2012-09-10 03:50:06 補充：
It must NOT be H2O(g).
For ideal gases, there is no interaction between gaseous molecules.

What do u mean by H2O? Is it H2O(l) or H2O(g)?

1. HF - one hydrogen bond / molecule
2. H2O - two hydrogen bonds / molecule
3. NH3 - one hydrogen bond / molecule
4. methanol - one hydrogen bond / molecule