Question

The neutral OH molecule has been implicated in certain ozone-destroying processes which take place in the upper atmosphere.

a) Electron affinity can be defined for molecules just as it is defined for single atoms. What is the complete chemical equation representing the electron affinity of OH. Include all relevant state symbols ((s), (g), etc.)

b) Assuming that the electron added to OH is entirely localized in a single atomic orbital on one atom, identify which atom (O or H) is probably accepting the electron, and the n and l quantum numbers of the atomic orbital that is doing so.

c) The electron affinity of OH has been measured to be similar, but slightly more negative than the electron affinity of single O atoms. Explain briefly why the electron affinity is similar but slightly more negative.

Answer 1

a.OH_(g) + e^- OH^-_(g)

b. Oxygen is more electronegative than hydrogen. Therefore, Oxygen is probably accepting the electron. The n and l quantum numbers of the atomic orbital doing so are 2 and 1 respectively.

c. Electron affinity of an atom or molecule is defined as the energy change when an electron is added to a neutral atom or molecule to form a negative ion. When energy is released, the change is negative. In both cases, the energy change is negative. But it is slightly more negative in the case of OH because this radical has a higher amount of initial energy than single O atoms. So when then are brought down to the same initial level from different starting points, one of which is higher in energy, the change is going to be slightly more in that case. That is what is happening here.