Problem 151 - A Complete Resource Book in Chemistry for JEE Main

Question

In the coordination compound \(\left.\mathrm{K}_{4} \mathrm{Ni}(\mathrm{CN})_{4}\right]\), the oxidation state of nickel is (a) \(-1\) (b) 0 (c) \(+1\) (d) \(+2\)

Step-by-Step Solution

Answer

The oxidation state of nickel in \([\text{K}_4\text{Ni}( ext{CN})_4]\) is 0.

Step 1: Write the formula

The coordination compound given is \([\text{K}_4\text{Ni}( ext{CN})_4]\). We need to identify the oxidation state of nickel (Ni) in this compound.

Step 2: Identify known charges

The potassium ion (K) typically has a charge of \(+1\), and each cyanide ion (CN) has a charge of \(-1\).

Step 3: Determine the overall charge

Since the formula given is part of a complete compound (outside the brackets) and there is no charge denoted outside the brackets, the charge of the entire compound is 0.

Step 4: Calculate the charge of all components except nickel

Potassium contributes a total charge of \(+4\) (4 x \(+1\)) since there are four potassium ions. Cyanide contributes a charge of \(-4\) (4 x \(-1\)) since there are four cyanide ions.

Step 5: Calculate the oxidation state of nickel

The sum of all charges in the compound must equal the overall charge. Let x be the oxidation state of nickel. Then, using the equation:\[ 4(+1) + x + 4(-1) = 0 \]Solving for x gives:\[ 4 - 4 + x = 0 \]Thus, \( x = 0 \).

Step 6: Conclude the oxidation state

The oxidation state of nickel in the compound \([\text{K}_4\text{Ni}( ext{CN})_4]\) is 0.

Key Concepts

Coordination Compounds

Coordination compounds are fascinating marvels of chemistry where a central metal atom is bonded to a surrounding group of molecules or ions. These surrounding entities are known as ligands, and they're key to understanding how these compounds hold together. In a coordination compound, such as \([\text{K}_4\text{Ni}(\text{CN})_4]\), the central nickel atom is surrounded by cyanide ligands. This complex is involved in various reactions due to the unique bonding between the metal and its ligands.
A key feature of coordination compounds is their ability to form coordination spheres. Within this sphere, the central metal can interact with the ligands, creating a stable structure. This setup allows coordination complexes to have diverse shapes and properties, such as geometric isomerism or optical activity.
To understand these compounds, focus on:

• The central metal atom or ion: It coordinates with ligands.
• Ligands: These are ions or molecules that donate pairs of electrons to the metal.
• The overall geometry of the compound can affect chemical properties.

Coordination compounds are not only theoretical; they're highly applicable in real-world scenarios, such as catalysis, medicine, and materials science.

Transition Metals

Transition metals are a vital group of elements in the periodic table. They occupy the central block, specifically the d-block, between group 3 to group 12, and they're characterized by their variable oxidation states. Nickel, for instance, is a transition metal that can exhibit different oxidation states in various compounds.
Transition metals are renowned for their ability to form these distinctive classes of compounds, like our \([\text{K}_4\text{Ni}(\text{CN})_4]\), due to the d-orbitals' involvement in bonding. But why can transition metals handle multiple oxidation states? This is because they can lose different numbers of electrons from their s and d subshells. The flexibility in electron configuration provides them with unique chemical behaviors and makes them crucial in industrial processes.
Some features of transition metals include:

• They often form colored compounds.
• Many are good conductors of electricity.
• They're often used as catalysts in chemical reactions.

Understanding transition metals allows us to appreciate their role in both inorganic and bioinorganic processes. They are indeed essential for technological advances.

Chemical Bonding

Chemical bonding is the glue that holds atoms together in molecules and compounds. In coordination compounds, the type of chemical bonding is slightly different. We often encounter both ionic and covalent character in the bonds. For instance, in \([\text{K}_4\text{Ni}(\text{CN})_4]\), the bonds between potassium and the rest of the complex exhibit ionic characteristics due to the transfer of electrons.
Within the coordination sphere itself, especially between the central nickel and cyanide ions, we see coordinate covalent bonds. Here, the ligands donate electron pairs to the metal center. This donation of electrons emphasizes the donation-receiving nature of coordinate bonds.
The key points about chemical bonding in these complexes include:

• Ionic bonding involves electron transfer between atoms.
• Coordinate covalent bonding involves the sharing of electron pairs.
• The type of bonding defines the physical and chemical properties of the compound.

Understanding these bonding types is crucial for grasping how compounds interact and react, enabling chemists to predict behaviors and synthesize new materials.