A reaction sequence in which an intermediate of reduced coordination number is formed by the departure of the leaving group is called:

Ch4 and ph3 are both covalent since they are composed both of non-metals.    ch4 is non- polar because of  london forces and has a geometry of tetrahedral  ph3 , on the other hand, is umbrella shaped polar and has dipole-dipole intermolecular force (imf) . since ph3 is polar, it has a stronger imf   

The closer the atoms are to becoming ionic the more highly dense the negatively charged side gets.