2.2 Water

Question 1

Water structure

Answer 1

Water is made up of two hydrogen atoms covalently bonded to an oxygen atom (molecular formula = H₂O).

Question 2

Define polarity

Answer 2

A slight charge difference across the different poles of the molecule.

Question 3

Why is water molecule polar?

Answer 3

Oxygen has a higher electronegativity and attracts the shared electrons more strongly, resulting in polarity.

Question 4

What allows water to form associations with polar molecules?

Answer 4

Dipole allows water to form weak associations with other polar molecules (The slightly negative poles (δ–) will attract the slightly positive poles (δ+) of other molecules, and vice versa).

Question 5

Hydrogen bonding

Answer 5

Hydrogen bonding is a type of dipole-dipole attraction between molecules. It results from the attractive force between a hydrogen atom covalently bonded to a very electronegative atom such as a N, O, or F atom. They are relatively stronger than other polar associations due to the high electronegativity of N, O and F.

Question 6

Thermal propeties of water

Answer 6

Water can absorb much heat before changing state (requires breaking of hydrogen bonds).

Question 7

Cohesive/adhesive properties of water

Answer 7

Water will ‘stick’ to other water molecules (cohesion) and charged substances (adhesion).

Question 8

Solvent properties of water

Answer 8

Water dissolves polar and ionic substances (forms competing polar associations to draw materials apart).