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Textbook Question
Mercury in the environment can exist in oxidation states 0,
+1, and +2. One major question in environmental chemistry
research is how to best measure the oxidation state of mercury
in natural systems; this is made more complicated by the
fact that mercury can be reduced or oxidized on surfaces differently
than it would be if it were free in solution. XPS, X-ray
photoelectron spectroscopy, is a technique related to PES (see
Exercise 7.111), but instead of using ultraviolet light to eject valence
electrons, X rays are used to eject core electrons. The energies
of the core electrons are different for different oxidation
states of the element. In one set of experiments, researchers
examined mercury contamination of minerals in water. They
measured the XPS signals that corresponded to electrons ejected
from mercury's 4f orbitals at 105 eV, from an X-ray source
that provided 1253.6 eV of energy 11 ev = 1.602 * 10-19J2.
The oxygen on the mineral surface gave emitted electron energies
at 531 eV, corresponding to the 1s orbital of oxygen.
Overall the researchers concluded that oxidation states were
+2 for Hg and -2 for O. (b) Compare the energies of
the 4f electrons in mercury and the 1s electrons in oxygen
from these data to the first ionization energies of mercury
and oxygen from the data in this chapter.
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