Compound reference
Phosphorus trichloride
PCl₃
The chemistry
Same pyramid as ammonia, scaled up. Period-3 P has a lone pair just like N; it pushes the three Cl bonds into a tighter pyramid (~100°).
Remember it as…
Same shape as NH₃ - three bonds + one lone pair. Bigger central atom (P > N) → tighter angle (~100° vs ~107°).
Common mix-up
PCl₃ has the same shape FAMILY as ammonia (trigonal pyramidal), not the same angle. Going down a group, the central atom gets bigger and the bond angle SHRINKS - the bonding orbitals get more p-like.
Where the name comes from
Phosphorus from Greek phōs (light) + phoros (bearing) - "light-bearer." White phosphorus glows in the dark from slow oxidation, which is how Brand discovered it in the 1660s.
Where you meet it
Industrial precursor for pesticides, flame retardants, and pharmaceuticals; reacts violently with water to give phosphorous acid + HCl.
PubChem facts
- IUPAC name
- trichlorophosphane
- Molecular weight
- 137.33 g/mol
Also known as: phosphorus(III) chloride
Handling note
Reacts violently with water to release corrosive, toxic fumes, and is corrosive and toxic itself; always handled under dry, inert conditions.
BondingMolecular geometry
Chemical data from PubChem (NIH/NCBI)