 Solution

ID: past-exam-of-the-chemistry-a-course-of-the-university-of-cambridge/2024/paper-1/a4/a/ii/solution

One choice is the C2v molecular point group,

{E, C_{2} (z), σ_{x z}, σ_{yz}}

. The additional operation is a second reflection, since

C_{2} (z) σ_{x z} = σ_{yz} .

A bent water molecule has this symmetry. Choose the

z

axis along its bond-angle bisector and put the molecule in the

x z

plane: reflection in

yz

exchanges its two hydrogen atoms, while reflection in

x z

fixes their positions.

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