intermolecular forces

why are intermolecular forces so weak

distance between molecules is larger than chemical bonds — electrostatic strength decreases over distance

types of intermolecular forces

1. dipole-dipole

   • polar molecules, partial positive & negative attraction

     • strength measured by boiling points

2. london dispersion

   • non-polar molecules, get close enough, become slightly polar & condense

hydrogen bonding

type of dipole-dipole attraction

• hydrogen with oxygen, nitrogen

  • causes water to freeze crystal-like: less dense than liquid

london dispersion forces

• can be interrupted by motion

• strength dependent on polarizablity : increases with higher atomic/molecule size

how do intermolecular forces affect properties of states of matter

• liquids are denser & less compressible (than gases) + have definite volume but not size or shape

• solids are locked into place

interparticle attractions related to states of matter

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polarizability

the ease with which the electron cloud of an atom can be distorted by an electric field (becoming polar)

how does polarizability relate to dispersion forces

as non-polar molecules get closer together they can polarize and combine

viscosity

liquid’s resistance to flow

surface tension

property allowing a liquid surface to behave like a stretched membrane

how do the states of matter relate to the strength of intermolecular forces

• strong intermolecular forces = solids

• medium intermolecular forces = liquids

• weak intermolecular forces = gases

how does adding or removing energy cause a phase change

with more or less energy the particles can overcome or succumb to intermolecular forces, changing state changes