Problem 36 - Chemistry The Central Science In Si Units

Question

Write the formula for each of the following compounds, being sure to use brackets to indicate the coordination sphere: (a) hexaammineiron(II) nitrate (b) tetraaquadibromochromium(III) perchlorate (c) ammonium hexachloropalladate(IV) (d) diammineoxolatonickel(II) (e) Hexaamminemolybdenum(III) tetrachlorocuprate(II)

Step-by-Step Solution

Answer

(a) \([\text{Fe(NH}_3)_6]\text{(NO}_3)_2\) (b) \([\text{Cr(H}_2\text{O})_4\text{Br}_2]\text{(ClO}_4)_2\) (c) \((\text{NH}_4)_2[\text{PdCl}_6]\) (d) \([\text{Ni(NH}_3)_2\text{(ox)}]\) (e) \([\text{Mo(NH}_3)_6][\text{CuCl}_4]\)

Step 1: Identify the coordination complex

For each compound, identify the central metal, ligands, and the oxidation state of the metal. The coordination complex often involves the central metal surrounded by ligands. For example: - (a) Hexaammineiron(II): Central metal is iron (Fe), ligands are ammine (NH₃), and the metal's oxidation state is +2.

Step 2: Write the coordination complex chemical formula

Based on the step 1 data, write the chemical formula of the coordination complex using brackets to denote the coordination sphere and showing the ligands. - (a) Iron with 6 ammine ligands: \([\text{Fe(NH}_3\text{)}_6]^{2+}\)

Step 3: Identify and write the counter ions

Determine the counter ions for charge balance, often indicated outside the brackets. - (a) With nitrate as the counter ion: The formula is \([\text{Fe(NH}_3\text{)}_6]\text{(NO}_3\text{)}_2\).

Step 4: Repeat for each compound

Follow steps 1 to 3 for the remaining compounds:- (b) \([\text{CrH}_2\text{O}_4\text{Br}_2]^{+}\) with perchlorate as the counter ion: \([\text{CrH}_2\text{O}_4\text{Br}_2]\text{(ClO}_4\text{)}_2\)- (c) Ammonium counter ion with hexachloropalladate: \((\text{NH}_4)_2[\text{PdCl}_6]\)- (d) Diammineoxolatonickel: \([\text{Ni(ox)(NH}_3)_2]\)- (e) Hexaamminemolybdenum(III) with the tetrachlorocuprate counter ion: \([\text{Mo(NH}_3)_6][\text{CuCl}_4]\)

Key Concepts

Coordination Compounds

Coordination compounds, also known as coordination complexes, are fascinating structures where a central metal atom is surrounded by molecules or ions called ligands. These ligands are bound to the metal through coordinate covalent bonds, creating a specific geometry and chemical identity for the compound.

To understand coordination compounds, it's essential to grasp the concept of a coordination sphere, which includes the central metal and all the ligands attached to it in a definite stoichiometric arrangement.

• This sphere is usually denoted by square brackets in formulas.
• Outside these brackets often lies a counter ion, which balances the overall charge of the compound.

In coordination chemistry, it's the unique interaction between the central metal and its ligands that imparts special properties to these complexes, making them significant in various fields, such as catalysis, biology, and materials science.

Oxidation States

Oxidation state, or oxidation number, plays a vital role in coordination chemistry. It refers to the hypothetical charge that an atom would have if all bonds to atoms of different elements were fully ionic. Understanding oxidation states aids in determining the electronic structure, reactivity, and magnetic properties of the coordination compound.

For a central metal in a coordination compound, the oxidation state can be figured out by considering the charge of the ligands and the overall charge of the complex.

• For instance, if a complex has a +2 charge and the ligands are neutral, the metal's oxidation state will largely determine the complex's charge.
• Identifying oxidation states helps in predicting the compound's behavior in different chemical reactions.

A clear understanding of oxidation states not only helps in naming and writing formulas for coordination compounds but also in exploring their chemical nature.

Ligands

Ligands are crucial to the formation and characteristics of coordination compounds. They are ions or molecules that donate a pair of electrons to the central metal atom forming a coordinate covalent bond. This relationship has a profound effect on the geometry and stability of the complex.

Ligands are classified based on several factors:

• Charge: Neutral ligands like water (H₂O) or ammine (NH₃) have no charge, while charged ligands like chloride (Cl⁻) possess a charge.
• Denticity: This refers to the number of donor groups a ligand has. For example, "bidentate" indicates two donor sites, such as in an oxalate ion (ox).
• Size and Sterics: Larger ligands may cause the complex to adopt different geometries due to spatial considerations.

The nature and types of ligands significantly affect the resulting properties of a coordination compound, including its color, magnetic behavior, and solubility.

Central Metal Atom

At the heart of any coordination compound is the central metal atom, which forms the core around which the ligands are assembled. This central atom is typically a transition metal, known for its ability to exhibit a variety of oxidation states and coordinate to multiple ligands.

The choice of the central metal atom is crucial as it influences the properties of the entire coordination compound:

• Electronegativity and Ionic Radius: These factors affect the metal's ability to bind to specific ligands.
• Electronic Configuration: This dictates the geometry and color of the complex, as well as its electronic properties.
• Stability: Different metals contribute to the stability or reactivity of the complex based on their position in the periodic table.

Comprehending the role of the central metal is key to predicting how a coordination compound may behave in chemical reactions or applications, such as catalysis or biological systems.