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Chemistry LibreTexts

Oxidation States (Worksheet)

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    127049
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    Work in groups on these problems. You should try to answer the questions without referring to your textbook. If you get stuck, try asking another group for help.

    Learning Objectives

    • Predict available oxidation states for s- and p-block elements.
    • Predict available oxidation states for d-block elements of period 3.
    • Provide specific reasoning for the most common oxidation states of 3d elements.

    Oxidation states of elements in a compound provide information about size, structure, and chemical reactivity of the compound. Differences in the oxidation state of inorganic transition metals lead to vastly different properties of the particular element or the transition metal complex of which it is a part. This change in the behavior and properties of inorganic transition metal complexes is extremely important and widely used in biological molecules and synthesized complexes alike.

    Critical Thinking Questions

    1. Is there a correlation between ionization energies of certain elements and the elements’ most stable oxidation states? If so, what predictions about oxidation states of an element can be made from ionization energy values for that element? (Reminder: Ionization energy (IE) is defined as the energy required to remove an electron from a gaseous atom or ion. The energy required to remove the highest-energy electron of an atom is referred to as the first ionization energy (IE1); the energy required to remove the second highest-energy electron of an atom is referred to as the second ionization energy (IE2).
    2. The most common oxidation states of some elements can be predicted based on the element’s position in the periodic table, while this is not the case for all elements. List those groups of the periodic table, for which the oxidation states are known based on the group number (also list the corresponding oxidation states).
    3. The most common oxidation states of transition metals can be predicted only to a limited extent from the element’s position in the periodic table. Use your knowledge of inorganic transition metal complexes to list your predictions for the most common oxidation states of all 3d transition metals.

    Model 1: Examples of some historic four- and six-coordinate inorganic transition metal complexes:

    [Co(NH3)6]Cl3 (NH4)2[Mn(H2O)Cl4]
    K3[Fe(CN)6] [Fe(H2O)4Cl2]
    [Cu(NH2CH2COO)2] [Ti(NH3)6]Cl4
    [Ni(NH3)4(H2O)2]SO4 [Pd(NH3)4][Pd(Cl)4]
    [Cr(NH3)5Cl]Cl2 [Pt(NH3)4][Pt(Cl)4]
    1. List the oxidation states of all transition metal ions in Model 1. Compare these oxidation states to your predictions from question 3. Do they match or are there deviations?
    2. Write out the valence electron configuration of all transition metal ions in Model 1.
    3. Provide some reasoning as to why each of these particular oxidation states is the (or one of the) most stable oxidation states for each of the metals in questions 4 and 5 (Note: this will be more straight-forward for some elements than for others).
    4. Are there 3d transition metals that commonly occur in complex ions having oxidation states other than the ones listed above? If so, list these oxidation states and corresponding electron configurations and provide some explanation as to why they are particularly stable.
    5. Draw a typical energy level diagram of 3d orbitals of a free ion and a typical energy level diagram of 3d orbitals, when the corresponding ion is part of a six-coordinate coordination compound. Label the orbitals and briefly explain why the energy levels change when a free metal ion is coordinated to six ligands.
    6. Draw a typical energy level diagram of 3d-orbitals when part of a four-coordinate coordination compound. Label the orbitals and explain why the electronic arrangement in a four-coordinate complex differs from that of a six-coordinate complex.
    7. Can the energy level diagrams from questions 8 and 9 provide some additional information as to why a certain oxidation state is most common/stable for a particular element? If so, list some case that can be explained using these energy level diagrams. Refer back to question 6 and explain your reasoning.
    8. Consider the energy level diagrams of 3d-orbitals when part of a six-coordinate complex (see question 8). Do the electrons always occupy all lower-energy orbitals first before occupying the higher-energy orbitals? Are there cases where higher-energy orbitals are occupied (with up to one electron each) before all lower-energy orbitals are completely filled?
    9. What condition must be true for this to happen? Consider the relative energies associated with each process.
    10. Some d-electron configurations would not be affected by the scenario described in question 11 (i.e. by filling of higher-energy orbitals with up to one electron each before lower-energy orbitals are filled). State which of the d-electron configurations d1 – d10 would be unaffected by this difference in the filling of electronic orbitals, and which ones would be affected by it.
    11. Consider those d-electron configurations, for which it makes a difference whether or not the lower-energy orbitals are filled before any electrons occupy the higher-energy orbitals. Make a suggestion as to what could be responsible for favoring one over the other electron configuration that could result in these cases. In other words, when is the one electron configuration favored (i.e. filling of all lower-energy orbitals before any electrons occupy higher-energy orbitals), and when is the other favored (i.e. not all lower-energy orbitals are completely filled when higher-energy orbitals are being filled with up to one electron each)?
    12. Can the same scenario (of higher-energy orbitals becoming occupied before all lower-energy orbitals are completely filled) occur for four-coordinate coordination compounds? Use an electron level diagram of four-coordinate coordination compounds to support your answer.

    References

    • Jens-Uwe Kuhn, Santa Barbara City College
    • Jessica Martin, Northeastern State University