Hydrogen bonding

T or F: hydrogen bonding are bonds

Hydrogen bonding is an INTERMOLECULAR FORCE and they are much weaker than any covalent bond

When does hydrogen bonding occur?

occurs in compounds that have a H atom covalently bonded to one of nitrogen, oxygen and fluorine, which must have an available lone pair of electrons.

Why does hydrogen bonding occur here? Why are the three elements so electronegative?

large electronegativity difference between H and N/O/F.

Little shielding because one filled electron shell

draw the hydrogen bonding between 2 HF molecules

Bond angle of all hydrogen bonds

180^o

Why is this the bond angle for all hydrogen bonds?

Hydrogen has two areas of electron density

4 Properties hydrogen bonding gives water

•Surface tension

•Excellent solvent

•Liquid at room temperature

•Highly polar molecule

Hydrogen bonding in ice

In ice, each water molecule is hydrogen bonded to 4 other water

molecules. (So on average, the are two H-bonds per molecules) - Ice has an "open structure" with lots of spaces between

molecules - As a result the molecules are held further apart than in liquid

water - When the ice melts, the structure is lost and the molecules

collapse closer together. - This means ice is less dense than water (the same mass takes up

more volume)

- So ice floats on water.