Exam specific answers (bonding)

Question 1

explain how hydrogen bonding arises in a H-F molecule? (3)

Answer 1

there is a large difference in electronegativity between the H and F atom
this creates a permanent dipole-dipole/polar bond
an attraction is formed between the partially positive H atom and the lone pair on the F atom

Question 2

explain why the O-H bond in a methanol molecule is polar? (1)

Answer 2

oxygen is more electronegative than hydrogen

Question 3

give one reason why ice is less dense than water? (1)

Answer 3

hydrogen bonding in ice causes molecules to be held further apart than in liquid water

Question 4

the C-Br bond is polar - explain why CBr4 is not a polar molecule. (2)

Answer 4

the molecule has a tetrahedral shape, meaning the dipoles cancel out

Question 5

suggest, in terms of the intermolecular forces for each compound, why CBr4 has a
higher boiling point than CHBr3. (3)

Answer 5

• CBr4 has van der Waals forces between molecules
• CHBr3 has van der Waals and permanent dipole-dipole forces
• The van der Waals’ between CBr4 molecules are stronger than the dipole-dipole and van der Waals’ forces between CHBr3 (as it has more electrons)