Intermolecular Forces Flashcards
3 types of intermolecular forces
Van der waals
Permanent dipole-dipole
Hydrogen
What happens to the atoms when van der waals forces are presented
All atoms are attracted to one another
How are van der waals forces formed
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
How are van der waals forces affected by the size of the molecules
Larger molecules larger electron clouds
Because electrons are further from the nuclei
So has a higher boiling point
How are van der waals forces affected by the shape of the molecule
Long straight molecules lie close together so there are stronger forces between them
H2O vs H-F
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
If a substance has permanent dipole-dipole forces what will there be?
There will be weak electrostatic forces of attraction between delta positive and delta negative charges on neighbouring atoms
Draw diagram of permanent dipole dipole forces
H&+ — .—-CL&- :::::::: H&+ —.—-Cl&-
Practical of permanent dipole dipole forces
Electrically charged rod
Explain permanent dipole dipole forces practical
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
When do hydrogen bonds form?
Only when hydrogen covalently bonds to fluorine, nitrogen or oxygen
Why do hydrogen bonding form when hydrogen bonds to F2, N2 or O2
Because F2, N2 and O2 are very electronegative so draw bonding electrons away form H2 atom
How do hydrogen bonds form
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
What does hydrogen bonding give molecules
Much higher boiling and melting point
How should you finish boiling and melting point questions
Therefore takes more energy to break these forces
