Intermolecular forces Flashcards
where can you find intermolecular forces?
between covalent bonds
where are intramolecular forces?
inside each molecule
what are intermolecular forces?
the attractions between molecules
3 types of intermolecular forces
dipole dipole attraction
Van der waal attraction
hydrogen bonds
strength of Van der waal attraction
weakest
strength of dipole dipole attraction
medium strength
strength of hydrogen bonds
strongest
when does dipole-dipole attraction happen?
when a covalent molecule has permanent partial + and partial - charges due to having large electronegativity differences
where do van der waal forces occur
do not have dipole moments, non-polar covalent
what causes van der waal forces?
flickering dipoles
what causes flickering dipoles
due to their random movement within the orbitals, there are small lengths of time when the electrons are not equally shared
what does it mean for a flickering dipole to be ‘on’
inducing a temporary dipole
what point in time do van der waal forces occur
when the 2 molecules involved are both ‘on’
why does NO boil at much higher than N2
because van der waal forces are much weaker than dipole-dipole attraction
why does boiling point increase with Mr in non-polar covalent molecules
because the number of van der waal forces increases with Mr
what causes the great strength of polythene?
it is due to millions of van der waal forces betwee the parallel molecules
boiling points of hydrogen bonding
surprisingly high BP
when does a hydrogen bond occur?
when hydrogen in a covalent bond with N,O or F in one molecule AND there is a lone pair of electrons on either N,O or F on another neighbouring molecule
example of hydrogen bonding
in water
why are N,O and F significant in hydrogen bonding (2)
- very high electronegativity values
2. smallest atomic radii
why is Cl not involved in hydrogen bonding
atomic radius is too bigh
how much stronger is a covalent bond than a hydrogen bond
10 times stronger
where do you find hydrogen bonding between N and O
in biology; proteins, DNA etc.
why is ammonia extremely soluble in water?
becuase of hydrogen bonding