Problem 44 - Chemistry The Molecular Science

Question

In a complex ion, a central ruthenium ion, \(\mathrm{Ru}(\mathrm{III})\), is bonded to six ammonia molecules. (a) Give the formula and net charge for this complex ion. (b) How many chloride ions are needed to balance the net charge on this complex ion? (c) Write the formula for the compound formed by this complex ion and the chloride ions that are not part of it.

Step-by-Step Solution

Answer

1. \([\mathrm{Ru}(\mathrm{NH}_3)_6]^{3+}\) complex ion, net charge +3. 2. Three chloride ions needed. 3. Compound formula: \([\mathrm{Ru}(\mathrm{NH}_3)_6]\mathrm{Cl}_3\).

Step 1: Understand the Complex Ion

The complex ion has a central metal ion, ruthenium (III), denoted as \( \mathrm{Ru}^{3+} \), surrounded by six ammonia molecules, \( \mathrm{NH}_3 \), acting as neutral ligands.

Step 2: Determine the Formula of the Complex Ion

Since ammonia is a neutral ligand, it does not contribute to the charge of the complex ion. Thus, the formula of the complex is \([\mathrm{Ru}(\mathrm{NH}_3)_6]^{3+}\).

Step 3: Calculate the Net Charge of the Complex Ion

The central ruthenium ion has a +3 charge due to its oxidation state, while ammonia, being neutral, does not alter this charge. Therefore, the net charge of the complex ion is +3.

Step 4: Determine the Number of Chloride Ions Needed

To balance the +3 charge of the complex ion, you need 3 chloride ions (\( \mathrm{Cl}^- \)), each providing a -1 charge, making the total charge 0.

Step 5: Write the Formula for the Compound

Taking the complex ion \([\mathrm{Ru}(\mathrm{NH}_3)_6]^{3+}\) and combining it with 3 chloride ions \( (\mathrm{Cl}^-) \), the formula for the compound is \([\mathrm{Ru}(\mathrm{NH}_3)_6] \mathrm{Cl}_3\).

Key Concepts

Complex Ions

Complex ions are fascinating structures formed when a central metal ion binds with molecules or ions known as ligands. In these structures, the central metal ion is usually a transition metal, like ruthenium, which can donate empty orbitals to accommodate electron pairs from the ligands.

Transition metals are ideal for forming complex ions due to their ability to hold multiple oxidation states and coordinate with a variety of ligands. These complex ions often carry a charge, depending on the total charges of the metal center and surrounding ligands.

For example, in the ruthenium complex ion \([\mathrm{Ru}(\mathrm{NH}_3)_6]^{3+}\), the ruthenium ion with a +3 charge is at the center. This is balanced by neutral ammonia ligands, which means the overall charge is +3, as ammonia does not affect the overall charge of the complex.

Ruthenium Complexes

Ruthenium, a member of the platinum group metals, is known for its ability to form stable and diverse complexes. This is largely due to its large size and flexible oxidation states. In coordination chemistry, ruthenium often appears in higher oxidation states which allow it to bond with a variety of ligands.

In the complex \([\mathrm{Ru}(\mathrm{NH}_3)_6]^{3+}\), ruthenium takes on a +3 oxidation state. It acts as the central coordinating ion surrounded by six ammonia molecules. These molecules are bound in a symmetrical octahedral geometry, which is typical for six-coordinate complexes.

Ruthenium's appealing chemistry makes it useful in many areas, such as catalysis, synthetic reactions, and even therapeutic applications. Understanding complexes like \([\mathrm{Ru}(\mathrm{NH}_3)_6]^{3+}\) helps scientists design materials with tailored properties for specific applications.

Ligand Chemistry

In ligand chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a complex. Ligands can be neutral molecules, like ammonia, or charged ions, and they donate electron pairs to the metal center.

Ligands are crucial in determining the structure and properties of the complex ions they form. They can influence the color, reactivity, and the overall stability of the complex. Ammonia, for instance, is a neutral ligand, and forms coordinate covalent bonds with the ruthenium ion in the discussed ruthenium complex.

Because ligands like ammonia donate electrons to the metal ion, they play a decisive role in stabilizing the metal's oxidation state. The symmetrical arrangement around the ruthenium in \([\mathrm{Ru}(\mathrm{NH}_3)_6]^{3+}\) showcases the versatile nature of ligand chemistry. This coordination allows for the fine-tuning of the complex's characteristics, aiding in applications across various chemical fields.