The Lewis structure for PCl₃ shows the distribution of the valence electrons. 

Group 15 P (5 × 1)	5 electrons
Group 17 Cl (7 × 3)	21 electrons
total electrons available	26 electrons
used in single bonds (3 × 2)	-6 electrons
complete octets at Cl (6 × 3)	-18 electrons
	2 electrons
complete octets at P (2)	-2 electrons
remaining to be allocated	none

The general guidelines used in drawing this Lewis structure:

1. Count available electrons. The number contributed by each atom is the last digit of its Group number in the periodic table.
2. Connect bonded atoms by single bonds. Subtract two electrons per bond from the total available electrons.
3. Complete octets at outer atoms other than hydrogen (has two electrons maximum). Subtract the number of electrons used from the total.
4. Place any remaining electrons at the central atom.