Question

What is the electron configuration for the transition metal ion in each of the following compounds? a. \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) b. \(\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right] \mathrm{Cl}\) c. \(\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right] \mathrm{Br}_{2}\) d. \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\left(\mathrm{NO}_{2}\right)_{2}\right] \mathrm{I}\)

Short answer

The electron configurations for the transition metal ions in each compound are: a. Fe³⁺: \( [Ar] 3d^5 \) b. Ag¹⁺: \( [Kr] 4d^{10} \) c. Ni²⁺: \( [Ar] 3d^8 \) d. Cr¹⁺: \( [Ar] 3d^5 \)

Step-by-step solution

Determine the oxidation state for each transition metal

: For each compound, we will determine the charge of the transition metal ion based on the charges of the coordination complex and counterions. a. In \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\), the potassium ions have a charge of +1, and the coordination complex has a charge of -3. Thus, the charge on the Fe ion must be +3. b. In \(\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right] \mathrm{Cl}\), the chloride ion has a charge of -1, and the coordination complex has a charge of +1. Thus, the charge on the Ag ion must be +1. c. In \(\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right] \mathrm{Br}_{2}\), the bromide ions have a charge of -1 each, and the coordination complex has a charge of +2. Thus, the charge on the Ni ion must be +2. d. In \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\left(\mathrm{NO}_{2}\right)_{2}\right] \mathrm{I}\), the iodide ion has a charge of -1, and the coordination complex has a charge of +1. Thus, the charge on the Cr ion must be +1.

Electron configuration of neutral atoms

: Now, we will determine the electron configuration of the neutral atoms of each transition metal. a. Fe: \([Ar] 3d^6 4s^2 \) b. Ag: \([Kr] 4d^{10} 5s^1 \) c. Ni: \([Ar] 3d^8 4s^2 \) d. Cr: \([Ar] 3d^5 4s^1 \)

Electron configuration of transition metal ions

: Finally, we'll determine the electron configuration of each transition metal ion based on the oxidations states we found in step 1. Remember to remove electrons from the outermost shell (higher n value) first. a. Fe³⁺: \( [Ar] 3d^6 4s^2 \) --> remove three electrons: \( [Ar] 3d^5 \) b. Ag¹⁺: \( [Kr] 4d^{10} 5s^1 \) --> remove one electron: \( [Kr] 4d^{10} \) c. Ni²⁺: \( [Ar] 3d^8 4s^2 \) --> remove two electrons: \( [Ar] 3d^8 \) d. Cr¹⁺: \( [Ar] 3d^5 4s^1 \) --> remove one electron: \( [Ar] 3d^5 \) The resulting electron configurations are: a. Fe³⁺: \( [Ar] 3d^5 \) b. Ag¹⁺: \( [Kr] 4d^{10} \) c. Ni²⁺: \( [Ar] 3d^8 \) d. Cr¹⁺: \( [Ar] 3d^5 \)

Key concepts

Oxidation States

An oxidation state, also known as an oxidation number, is a number that helps us understand the degree of oxidation or reduction of an atom in a chemical compound. It tells us how many electrons an atom in a substance has gained, lost, or shared in forming the compound. This concept is crucial because it helps in determining the electron configuration of transition metal ions.

To find the oxidation state of transition metals in coordination complexes, you need to consider the charges of all components involved:

• Identify the charge of the whole complex and the counterions.
• Calculate the oxidation state of the central transition metal by balancing charges of the entire complex. For example, in \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\), the potassium ions each have a +1 charge, which adds up to +3. The complex itself holds a -3 charge due to the cyanide ions, making the oxidation state of iron +3.

This understanding helps build the foundation needed to configure electrons for transition metal ions by recognizing where electron loss occurs to form specific ions.

Transition Metals

Transition metals are elements found in the middle of the periodic table, typically within groups 3 through 12. Known for their unique electronic configurations, these metals have partially filled d orbitals. This gives rise to their special properties such as colorful compounds, multiple oxidation states, and formidable catalytic abilities.

Electron configuration in transition metals typically involves:

• Filling the 4s orbital before the 3d orbital when in the neutral atom state; however, during ion formation, electrons are removed from the 4s orbital first.
• The ability to access d orbitals leads to variability in oxidation states. For instance, iron (Fe) can have oxidation states of +2 or +3, among others, due to its electronic arrangement.

Understanding these configurations is essential for explaining the behavior of these metals, especially in forming complex ions where coordination and variable oxidation states are key factors. It’s this electronic versatility that allows transition metals to interact intricately with other molecules, forming stable and, often, biochemically significant molecules.

Coordination Complexes

Coordination complexes are structures where a single metal atom or ion, known as the central atom, is surrounded by molecules or anions called ligands. These ligands form coordinate covalent bonds with the central metal, donating electron pairs.In coordination complexes:

• The number of coordinate bonds or the coordination number often influences the geometry and properties of the complex. Common geometries include octahedral, tetrahedral, and square planar.
• Ligands can affect the electron configuration of the central metal atom by influencing oxidation state and electron distribution. For example, the complex \[\mathrm{Ni}(\mathrm{H}_{2} \mathrm{O})_{6}\]\ is octahedral, affecting how electrons in nickel are configured, explaining its particular oxidation state and behavior.

Coordination complexes are widely studied in chemistry because they exhibit fascinating chemical behaviors, such as varying colors and reactivity, which can be attributed to the d-to-d electronic transitions within the metal ion. Understanding how ligands impact these electron arrangements provides insight into the reactivity and applications of these complexes in catalysis and material synthesis.