there is repulsion between lone pair and bond pair for example in water molecule oxygen has lone pair which repells the bond pair due to this bond angle decreases simply ddue to repulsion btween lone pair to lone pair or lone pair to bond pair angle varies

NF3 has trigonal pyramidal shape.

Around nitrogen, there are 1 lone pair electron and 3 bond pair electrons.

The lone pair-bond pair electron repulsion is greater than bond pair-bond pair electron repulsion.

The angle between N-F bond pairs are 107 degrees

The difference between bonded and lone pair is that a bond pair is composed of two electron that are in a bond whereas lone pair is composed of two electron that is not a bond.

There are 3 bonding pairs of electrons N - H and one lone pair .

The repulsion forces between lone pair -lone pair is > lone pair -bond pair > bond pair - bond pair. So the lone pair causes distortion from a perfect tetrahedron

It doesn't exactly occupy more space, but it has a different shape to a bond pair. In a bond pair we have two positive nuclei, with most of the density of the bonding electron pair between the atoms. The outer nucleus attracts the bond pair outwards from the central atom. In a lone pair there is only the central atom to attract the electrons, so they are pulled in more than the bond pair, producing a fatter, squatter shape. This means that more of the electron density is near the central atom than with a bond pair, which makes it more effective at repelling the other electron pairs. Thus there is a difference in the amount of repulsion between different sorts of pair, meaning that he angles between them are different too, in the order, from greatest to least, lone pair-lone pair, lone pair-bond pair, bond pair-bond pair.