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.

Verified step by step guidance

1. Identify the given data: The energy of the X-ray source is 1253.6 eV, the energy of ejected 4f electrons from mercury is 105 eV, and the energy of ejected 1s electrons from oxygen is 531 eV.
2. Understand the concept: X-ray photoelectron spectroscopy (XPS) measures the binding energy of core electrons by using X-rays to eject them. The binding energy is the difference between the energy of the incident X-ray and the kinetic energy of the ejected electron.
3. Calculate the binding energy for mercury's 4f electrons: Subtract the kinetic energy of the ejected 4f electrons (105 eV) from the energy of the X-ray source (1253.6 eV).
4. Calculate the binding energy for oxygen's 1s electrons: Subtract the kinetic energy of the ejected 1s electrons (531 eV) from the energy of the X-ray source (1253.6 eV).
5. Compare these calculated binding energies to the first ionization energies of mercury and oxygen, which are typically provided in the chapter's data, to understand the relative energy levels and oxidation states.

Key Concepts

Oxidation States

Oxidation states indicate the degree of oxidation of an atom in a compound, reflecting the number of electrons lost or gained. For mercury, the common oxidation states are 0, +1, and +2, with +2 being the most stable in many compounds. Understanding these states is crucial for analyzing chemical behavior and reactivity, especially in environmental contexts where mercury interacts with various substances.

X-ray Photoelectron Spectroscopy (XPS)

X-ray Photoelectron Spectroscopy (XPS) is an analytical technique used to determine the elemental composition and chemical state of materials. It works by irradiating a sample with X-rays, causing core electrons to be ejected. The kinetic energy of these ejected electrons is measured, allowing researchers to infer the oxidation states of elements, such as mercury, based on the energy levels of the electrons involved.

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom or ion in its gaseous state. It is a key factor in understanding the reactivity and stability of elements. Comparing the ionization energies of mercury and oxygen with the energies measured in XPS helps to confirm the oxidation states of these elements, as higher ionization energies typically correlate with more stable oxidation states.