Exercises: Geometry, hybridisation and polarity

Carbon dioxide, $\mathrm{CO_2}$, and water, $\mathrm{H_2O}$, are triatomic molecules with polar bonds due to the high electronegativity of oxygen compared with that of carbon and hydrogen. However, their behaviour in an electrostatic field is radically different. The following illustration shows the spatial orientations and bond dipole moments for both substances:

1. a) Justify the molecular geometry of both species using VSEPR theory (specify the $\mathrm{AX}_n\mathrm{E}_m$ notation).
2. b) Deduce, from the vector sum of the bond dipole moments, whether or not each molecule has a resultant molecular dipole moment.