IMFs and properties of liquids

intramolecular forces

occur between atoms, we’re familar with already (ionic, covalent, metallic

intermolecular forces (IMFs)

between molecules with partial charges or between ions and molecules, weaker than intra

effects of IMFs

increased in condensed states → increased boiling points

affect solubility of a compound and viscosity

IMFs depend on

polarity, polarizability, and interactions based on electric charge distributions

effect of IMFs on particles of same charge

move away from each other

effect of IMFs on particles of opposite charge

move towards each other

arrows on field lines indicate where

a positive charge would move

ion-dipole force

attraction between an ion and a polar molecule e.g. adding salt to water

dipole-dipole force

in presence of external field, positive pole of a polar molecule attracts another’s negative pole e.g. liquid water

greater molecular dipole moment leads to

greater dipole-dipole forces and more energy required to separate molecules → higher boiling point

hydrogen bonding

when H is bonded to a small highly electronegative atom with lone pairs e.g. N, O, F

effects of hydrogen bonding

quite a large force between the high charge difference, creating a large boiling point

polarizability

how easily an electron cloud around a nucleus can be distorted

down a group, polarizability

increases

across a period, polarizability

decreases

cations are _ polarizable than their atoms

less

anions are _ polarizable than their atoms

more

dispersion force

electric field from another molecule can cause an enhancement of a preexisting or induction of a new dipole moment

dispersion force is responsible for

condensed states of nonpolar molecules e.g. liquid helium

help keep molecules closer together by

lowering the temperature

only IMF between nonpolar molecules is

dispersion force

effect of molecular shape on dispersion forces

when molecules make more contact with each other, dispersion forces increase

ranking of IMFs in strength

H-bonding > dipole-dipole > dispersion forces

when comparing two nonpolar molecules IMFs, compare

polarizability (size) and shape (surface area)

effect of IMFs on boiling point, surface tension, and viscosity

as the forces get stronger, all three increase

different between liquids and gases in container

liquids conform to shape but not volume, while gas does both

cohesion

between liquid and itself, holding it together and causes droplets to be spherical

surface tension

quantifying cohesion, energy/surface area

molecules in interior vs molecules at interface with air

can form a max number of favourable interactions vs fewer interactions, so there is a net attraction downward because they prefer the interior

viscosity

how easily a liquid flows, because interactions must be broken and reformed

as temperature increases, viscosity

decreases because interactions are weaker

adhesion

between unlike molecules

capillary action

how liquid moves when put in a thin tube

concave meniscus forms when

cohesion < adhesion e.g. water and silica

convex meniscus forms when

cohesion > adhesion e.g. mercury and silica

on a greased glass plate, water

sticks to itself better, forming little droplets because cohesion > adhesion

ice is less dense than liquid water because

ice has an open structure due to H bonding, taking up more volume