6.3 intermolecular forces

between which molecules do London (induced dipole-dipole) forces exist?

all molecules, polar and non-polar

how is a London (induced dipole-dipole) force formed?

• movement of electrons produce a changing dipole in a molecule

• at any instant, an instantaneous dipole will exist but its position is constantly shifting

• the instantaneous dipole induces a dipole on a neighbouring molecule

• the induced dipole induces further dipoles on the neighbouring molecules, which then attract one another

what is the effect of more electrons on the strength of london forces and therefore boiling point?

more electrons:

larger instantaneous and induced dipoles

greater induced dipole-dipole interactions

stronger forces between molecules

increases boiling point as more energy needed to overcome forces

in what type of molecules do permanent dipole-dipole forces occur?

polar molecules

what holds molecules together in a simple molecular lattice?

weak intermolecular forces

what bonds the atoms within each molecule in a simple molecular lattice?

bonded strongly by covalent bonds

describe the melting and boiling points of simple molecular substances

low melting and boiling points

explain the melting and boiling points of simple covalent molecules

when the simple molecular lattice is broken down it is the weak intermolecular forces between molecules that break and not the strong covalent bonds between atoms. these weak intermolecular forces can be broken

describe the solubility of non-polar simple molecular substances

soluble in non-polar solvents and insoluble in polar solvents

describe the electrical conductivity of simple molecular substances

do not conduct electricity in solid or liquid state

explain the electrical conductivity of simple molecular substances

no mobile charge carriers