Hydrogen bonding

Question 1

What are Hydrogen bonds?

Answer 1

• Special type of permanent dipole-dipole interaction found between molecules containing a strongly electronegative atom with lone pairs (like oxygen, fluorine and nitrogen) and hydrogen atoms
• Hydrogen bond acts between a lone pair on a EN atom in one molecule and a hydrogen atom in a different molecule

Question 2

Why is water perfect for hydrogen bonding?

Answer 2

• Unlike others it has 2 lone pairs AND two hydrogens so it is not limited by anything.
• Due to H.Bonding water has anomalous properties

Question 3

Why is the ice less dense than water?

Answer 3

• Hydrogen bonds hold water molecules apart in an open lattice structure
• The water molecules in ice are further apart than in water. This is because water can form 4 hydrogen bonds and when all are formed, it makes the bond extend outwards which holds water molecules slightly apart as a tetrahedral lattice full of holes.
• Solid ice is less dense than liquid water and it floats. The holes in the open lattice structure collapses and molecules move closer making water more dense.

Question 4

Why does water have a relatively high melting and boiling point?

Answer 4

• Hydrogen bonds are extra forces

- More energy is needed to break hydrogen bonds in water