The correct answer for Is PCl3 non-polar or polar? Why?
Cl3 is polar, because of its trigonal pyramidal structure. Only 3 of the 5 valence electrons of the phosphorus are used for bonding with chlorine, so the other two are unshared. Since electron pairs want to stay as far as possible from each other, that means that the three bonds and the remaining pair form a tetrahedron. The three chlorine atoms are thus not in the same plane as the phosphorus atom. The fact that they are clustered in the same half-space makes for an asymmetry in the molecule (which does have a different kind of symmetry, namely 3-way rotational symmetry).
The reflectional asymmetry of the molecule, combined with the fact that chlorine is significantly more electronegative than phosphorus, makes the molecule polar.