Final answer:
To construct a model of phosphorus trichloride (PCl3), use one ball to represent the phosphorus atom, three balls for chlorine, and arrange them in a trigonal pyramidal shape with connections representing the bonds.
Step-by-step explanation:
To build a ball-and-stick model of phosphorus trichloride (PCl3), you would require one ball to represent the phosphorus (P) atom and three balls for the chlorine (Cl) atoms. Connect the phosphorus ball with three sticks arranged in a trigonal pyramidal shape to the chlorine balls, with the phosphorus atom at the apex and chlorine atoms at the vertices of the triangular base.
Each P-Cl bond in PCl3 represents a pair of shared electrons, creating a molecule with a pyramid-like structure with a lone pair of electrons on the phosphorus atom which is not visually represented in the model.