What is the molecular geometry of AsCl3 ? A) tetrahedral B) trigonal pyramidal C) trigonal planar D) T-shaped
The answer is B) trigonal pyramidal.
One arsenic trichloride molecule will have a total of 26 valence electrons - 5 from the arsenic atom and 7 from each of the three chlorine atoms.
The arsenic atom will be bonded to the three chlorine atoms through single bonds that account for 6 of the 24 valence electrons. Each of the chlorine atoms will have 3 lone pairs, which will bring the number of valence electrons used to 24
The remaining two valence electrons will be place on the arsenic atom as a lone pair.
The arsenic atom is surrounded by 4 regions of electron density, which means that its has a steric number equal to 4. According to VSEPR Theory, the molecular geometry will be trigonal pyramidal,
Here is a video which discusses VSEPR theory and the shapes of molecules.
Video from: Noel Pauller