Best Answer: NCl3 would have N as the central atom, then three Cl atoms would be spread around it. Lastly, there would be one lone pair of electrons attached to the central atom. It would look like ammonia in terms of molecular geometry - a trigonal pyramidal molecule (shaped like a tripod).
First of all, N is the central atom because it is the least electronegative of the atoms involved. The dipole moments are all directed away from the N towards the Cl atoms, since Cl is more electronegative than N. This would give a downward net dipole moment, which means that the molecule is polar.
To help you imagine this, try visualizing a tripod floating in the air. The tripod represents the geometry of this molecule. Then, imagine pulling all the legs of the tripod at once (imagine that the pull is the electronegativity of the Cl). Doing so pulls your floating tripod downward - thus, there is a net movement (like a net dipole moment). Having a net dipole moment not equal to zero means that the molecule is polar.
Lastly, here's a tip for atoms with at least three substituents: if the substituents (the atoms surrounding the central atom) are the same (for example, all are hydrogen or all are oxygen) and the central atom has no lone pair, then the dipole moments would all cancel out and the molecule will be polar. On the other hand, if they are all the same but the central atom has a lone pair attached, then the molecule would be polar.