To determine if PCl3 is polar or nonpolar, we need to first determine its geometry. This presumes knowing the rules for drawing a correct Lewis structure and you can find more details about Lewis structures here.
P is the central atom and there are 5 + 3×7 = 26 electrons. Each chlorine taking three lone pairs leaves the nitrogen with one lone pair:
The central atom has 3 atoms and a lone pair (SN = 4). Therefore, the electron geometry is tetrahedral while the molecular geometry is trigonal pyramidal
Now, the polarity: The first thing here is to determine if the P-Cl bond is polar. Depending on the difference in the electronegativity values, covalent bonds can be polar and nonpolar.
- If the difference in electronegativity is less than 0.5, the electrons are about equally shared between the two atoms, forming a nonpolar a covalent bond.
- If the difference in electronegativity is between 0.5 and 1.7, we have a polar covalent bond.
- A difference of 1.7 or higher is so large that the electrons are no longer shared, and an ionic bond is formed. Ionic bonds are formed between metals and nonmetals.
PCl3 is a polar molecule because the P-Cl bond is polar, and the three bonds are not equivalent to the lone pair which causes an asymmetrical distribution of bonding electrons in the molecule. This results in a permanent dipole directed towards the P-Cl bonds as drawn:
Check this 99-question multiple-choice quiz on Geometry and Hybridization:
Geometry and Hybridization Quiz
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