Intermolecular Forces

Question 1

3 types of intermolecular forces

Answer 1

Van der waals
Permanent dipole-dipole
Hydrogen

Question 2

What happens to the atoms when van der waals forces are presented

Answer 2

All atoms are attracted to one another

Question 3

How are van der waals forces formed

Answer 3

Electrons in charger clouds constantly moving
Electrons are more likely to be on one side than other
When electrons are more to one side, atom has temporary dipole
Dipole causes another temporary dipole on neighbouring atom
2 dipoles are attracted to one another
Electrons constantly moving so dipoles always being created and destroyed

Question 4

How are van der waals forces affected by the size of the molecules

Answer 4

Larger molecules larger electron clouds
Because electrons are further from the nuclei
So has a higher boiling point

Question 5

How are van der waals forces affected by the shape of the molecule

Answer 5

Long straight molecules lie close together so there are stronger forces between them

Question 6

H2O vs H-F

Answer 6

Water has higher boiling point because each water molecule can form 2 hydrogen bonds due to the two lone pairs in oxygen
Fluorine is more electronegative than oxygen but it can only form one hydrogen bond

Question 7

If a substance has permanent dipole-dipole forces what will there be?

Answer 7

There will be weak electrostatic forces of attraction between delta positive and delta negative charges on neighbouring atoms

Question 8

Draw diagram of permanent dipole dipole forces

Answer 8

H&+ — .—-CL&- :::::::: H&+ —.—-Cl&-

Question 9

Practical of permanent dipole dipole forces

Answer 9

Electrically charged rod

Question 10

Explain permanent dipole dipole forces practical

Answer 10

Put an electrically charged rod next to a water jet
Water moves towards rod
Polar liquid contains molecules with permanent dipoles
Molecules in liquid turn to opposite charger is attracted towards rod

Question 11

When do hydrogen bonds form?

Answer 11

Only when hydrogen covalently bonds to fluorine, nitrogen or oxygen

Question 12

Why do hydrogen bonding form when hydrogen bonds to F2, N2 or O2

Answer 12

Because F2, N2 and O2 are very electronegative so draw bonding electrons away form H2 atom

Question 13

How do hydrogen bonds form

Answer 13

Bond is so polarised, H2 has such a high density because its so small that H2 atoms form weak bonds with lone pairs of electrons on F2, N2, O2 or others

Question 14

What does hydrogen bonding give molecules

Answer 14

Much higher boiling and melting point

Question 15

How should you finish boiling and melting point questions

Answer 15

Therefore takes more energy to break these forces