states of matter - IMF Flashcards
(20 cards)
intermolecular forces definition
refers to all attractive and repulsive forces that exist between molecules and atoms, excluding bonds (=intramolecular forces)
what physical properties are influences by IMF?
melting/boiling point
viscosity (resistance to flow)
surface tension
cohesion/adhesion
why does surface tension occur?
this is because molecules on the surface have more energy than molecules within the fluid
cohesion definition
attraction of molecules to eachother
adhesion definition
attraction of molecules to a surface
what are the relative strengths of cohesive/adhesive forces in water? + proof + opposite example
in water adhesion > cohesion
this is seen as in a thin tube water will dip in the centre (measure from the bottom of the meniscus)
in mercury cohesion > adhesion so in a thin tube it forms a dome (measure from top of meniscus)
capillary action definition
the phenomenon where liquid is drawn up a thin/capillary tube in bulk due to the small diameter of the tube which means the adhesive forces are sufficient to increase the surface area of the liquid
what is coulombs law and what does it describe?
describes ionic interactions
F(r) = (q1q2) / 4πε₀r^2
where F = force experienced by q1 due to q2 (depends on r)
r = distance
q1 and q2 = 2 ions
ε₀ = permittivity in a vacuum
permittivity definition
how potential energy acts through the medium separating the charges - as if charges are separated by a medium (e.g. air, water) the potential energy of the interactions are reduced
represented by ε which = ε₀εr where εr = dimensionless relative permittivity
potential energy definition
a measure of the total work done in bringing together 2 atoms from an infinite distance to a distance of r
represented by U(r)
what are the 6 types of IMF from strongest to weakest?
hydrogen bonds
ion-dipole interactions
permanent dipole dipole interactions
london forces
van der waals
hydrophobic interactions
describe how hydrogen bonds work
one of the strongest IMF
formed between H attached to N, O or F and N, O or F via lone pairs
strongest when molecules have 3 atoms and 180 degree angle
describe how ion-dipole interactions work
formed between an ion and a molecule with a dipole
describe how permanent dipole-dipole interactions work
formed between molecules with no formal charge but a permanent polarity, often seen in asymmetric molecules with asymmetric electron distribution
describe how london forces work
aka instantaneous dipole-dipole interactions or dispersion forces, movement of electrons in a molecule can induce a dipole which induced a dipole in a neighbouring molecule, attracting each other (all molecules can form these)
describe how van der waals forces work
weak short range electrostatic forces between molecules arising from the interaction of electric dipole moments, strong in large numbers
describe how hydrophobic interactions work
the association of non-polar groups in aq systems, caused by unfavourable interactions between non-polar groups and water
what molecules have asymmetry?
all heteroatomic bonds have asymmetry as they have asymmetric electron distribution, this means they have dipoles
polarisability definition
the degree to which the electron cloud of an atom is influenced by a magnetic field
p = α E
where p = induced dipole moment
α = polarisability
E = strength of magnetic field
- shows us that strength of induced dipole moments depend on the ease at which the electron cloud can be perturbed
