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Chapter 23: Problem 36

Predict the number of unpaired electrons in the following complex ions: (a) \(\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]^{4-},(\mathrm{b})\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\)

Short Answer

Expert verified
There are 4 unpaired electrons in both \(\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]^{4-}\) and \(\left[\mathrm{Cr}\left(\mathrm{H}_{2}\mathrm{O}\right)_{6}\right]^{2+}\).

Step by step solution

01

Determine the Oxidation State of Chromium

Chromium is a transition metal and its oxidation state can be determined by charging the ligands. For \(\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]^{4-}\), the oxidation state is calculated as follows: since CN-1 is -1 and there are 6 of these, and the overall charge of the ion is -4, the oxidation state of Cr is +2.
02

Electron Configuration of Cr in its Oxidation State

The ground state electron configuration of Cr is [Ar] 3d5 4s1. The oxidation state of +2 means 2 electrons are lost. The 4s orbital is emptied before 3d because it has higher energy. Therefore, the electron configuration of Cr+2 is [Ar] 3d4.
03

Determine Number of Unpaired Electrons

There are 4 in the 3d orbital. In accordance with Hund's rule, each electron occupies its own d-orbital before pairing, hence there are 4 unpaired electrons.
04

Repeat Steps 1-3 for Other Complex Ion

Repeat step 1-3 to find the number of unpaired electrons for \(\left[\mathrm{Cr}\left(\mathrm{H}_{2}\mathrm{O}\right)_{6}\right]^{2+}\). The oxidation state of Cr is +2, and the electron configuration is [Ar] 3d4. Therefore, there are 4 unpaired electrons.

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Most popular questions from this chapter

The \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}\) complex is more labile than the \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}\) complex. Suggest an experiment that would prove that \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}\) is a labile complex.

Copper is also known to exist in the +3 oxidation state, which is believed to be involved in some biological electron-transfer reactions. (a) Would you expect this oxidation state of copper to be stable? Explain. (b) Name the compound \(\mathrm{K}_{3} \mathrm{CuF}_{6}\) and predict the geometry of the complex ion and its magnetic properties. (c) Most of the known Cu(III) compounds have square planar geometry. Are these compounds diamagnetic or paramagnetic?

Define the following terms: coordination compound, ligand, donor atom, coordination number, and chelating agent.

What is the origin of color in a coordination compound?

Write the formulas for each of the following ions and compounds: (a) bis(ethylenediamine)dichlorochromium(III), (b) pentacarbonyliron(0), (c) potassium tetracyanocuprate(II), (d) tetraammin eaquachlorocobalt(III) chloride.
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