Intermolecular forces Flashcards
what is intramolecularr forces
a force that holds the atoms within a molecule together
what is intermolecular forces
an electostatic force of attraction between molecules including dipole dipole, hydrogen bonds and disperson forces
how do disperson forces/induced dipoles occur
due to random movement of electrons within a molecule - produces a varying temporary dipole making a molecule temporarily polar
the dipole on one atom induces dipoles on nearby atoms
atoms are now attracted to each other by weak forces
how does strenght of disperson force increase
as size of molecule increase, it increases number of electrons in the molecule and then the strength of the disperson force increases
the more the electrons, the stronger the attraction and the more energy needed to separate the particles
is disperson force strength proportional to boiling/melting point
yes
what is dipole dipole attraction
polar molecules experience electrostatic attraction between the dipoles in neighbouring molecules
strength increases with increasing molecular polarity
strength increase with a higher degree of asymmetry in the shape of the molecule causing a larger imbalance in the bond dipoles
strength increase with increasing BP and MP
what is hydrogen bonding
extreme dipole dipole attraction - strongest of the three forces
attraction between a lone pair of electrons from and F, O or N and a H atom that is already covalently bonded to another F, O or N atom.
the small sizes of H, F, N and O concentrates the partial charge in a small volume thus leading to a high charge density.
solubility of like substances (non polar to non polar and polar to polar)
if they are able to form complimentary intermolecular forces, they are easily able to form those intermolecular forces between one another.
little resistance of mixing between molecules
solubility of polar solute in non polar solvent
polar solutes form stronger force of attraction with each other than they do with the non polar molecules.
this results in a resistance between the two
non polar solutes in polar solvents
polar solvents form stronger force of attraction between each other than they do with the non polar molecuels.
resuults in resistance between the two.
how does melting and boiling point increase
increase in number of electrons - increase in intermolecular forces in strength which means increase in melting and boiling point
what is vapour pressure
a measure of the tendency of a substance to evaporate (kPa)
To evaporate molecules must overcome the intermolecular forces keeping it in the liquid phase.
What is the relationship between intermolecular forces and vapour pressure?
As the strength of the intermolecular forces increases, vapour pressure deceases.
as the strength of the intermolecular forces increase, vapour pressure decreases.
weakest intermolecular forces have the highest vapour pressure
