Problem 81 - A Complete Resource Book in Chemistry for JEE Main

Question

The catenation tendency of \(\mathrm{C}, \mathrm{Si}\) and Ge is in the order \(\mathrm{Ge}<\mathrm{Si}<\mathrm{C}\). The bond energies (in \(\mathrm{kJ} \mathrm{mol}^{-1}\) ) of \(\mathrm{C}-\mathrm{C}\), Si-Si and Ge-Ge bonds, respectively are (a) \(348,180,167\) (b) \(180,167,348\) (c) \(348,167,180\) (d) \(167,180,348\)

Step-by-Step Solution

Answer

(a) 348,180,167

Step 1: Understanding Catenation

Catenation refers to the ability of an element to form bonds with itself, creating chains or rings. This property is highly dependent on the strength of the bonds formed between the atoms of that element.

Step 2: Relating Catenation to Bond Energies

The tendency for catenation increases with stronger bond energy. Therefore, elements with higher bond energies between their atoms demonstrate better catenation properties.

Step 3: Analyzing Given Bond Energies

The question provides options with bond energies: (a) 348 kJ/mol for C-C, 180 kJ/mol for Si-Si, and 167 kJ/mol for Ge-Ge. (b) 180 kJ/mol for Si-Si, 167 kJ/mol for Ge-Ge, and 348 kJ/mol for C-C. (c) 348 kJ/mol for C-C, 167 kJ/mol for Ge-Ge, and 180 kJ/mol for Si-Si. (d) 167 kJ/mol for Ge-Ge, 180 kJ/mol for Si-Si, and 348 kJ/mol for C-C.

Step 4: Determining the Correct Order Based on Bond Energies

The strongest bond among C-C (348 kJ/mol), Si-Si (180 kJ/mol), and Ge-Ge (167 kJ/mol) indicates the highest catenation tendency. Therefore, C with 348 kJ/mol shows the highest catenation, followed by Si, and then Ge, aligning with option (a) where C-C > Si-Si > Ge-Ge in bond energy and thus in catenation tendency.

Key Concepts

Bond Energies

Bond energy is a critical factor in understanding why certain elements can form extensive chains or networks. It refers to the energy required to break a bond between two atoms. Higher bond energies indicate stronger bonds, making it tougher to break them. This strength reflects the stability of the bond and, consequently, the structure that these bonds form.

In our example, the bond energies for carbon-carbon (C-C), silicon-silicon (Si-Si), and germanium-germanium (Ge-Ge) bonds are essential for determining their ability to form long chains—a process known as catenation. When comparing these three elements, carbon stands out with the highest bond energy of 348 kJ/mol. This high energy means C-C bonds are very stable, leading to excellent catenation properties. On the other hand, Si-Si bonds have a bond energy of 180 kJ/mol and Ge-Ge bonds have 167 kJ/mol, reflecting weaker bond strengths and thus less tendency for forming long chains.

Catenation and Element Bonding

Catenation is a unique characteristic that allows elements to link together, forming long chains or rings. Carbon is known for its outstanding ability to undergo catenation, allowing the formation of a vast array of natural and synthetic compounds. This attribute is chiefly due to the strength of carbon-carbon bonds, as they hold together efficiently against numerous chemical challenges.

While many elements can participate in catenation to some extent, few can match carbon's versatility. This is because carbon not only forms strong bonds with other carbon atoms but also creates stable configurations with additional elements like hydrogen, oxygen, and nitrogen. This versatility underpins the immense variety of organic compounds in nature.

Silicon and germanium also show some degree of catenation, but their weaker bonds reduce this tendency. Silicon, for example, can form extended chains found in silicones, but these are less stable compared to organic carbon chains. Germanium displays even less inclination towards catenation due to the weakest bond energies among these three elements.

Carbon-Silicon-Germanium Bond Comparison

When comparing carbon, silicon, and germanium, the key lies in examining their bond strengths and how these affect catenation. Carbon, with a bond energy of 348 kJ/mol, leads the group by a significant margin. This strong C-C bond allows carbon to form complex and stable chains, which constitute the backbone of organic chemistry.

Silicon's bond energy of 180 kJ/mol makes Si-Si bonds less stable than C-C bonds. Nevertheless, silicon does participate in catenation, forming chains and networks as seen in various silicate materials. Silicon compounds are crucial in the electronics and material sciences industries, showcasing impressive flexibility, though not as extensive as carbon.

Germanium, with a bond energy of 167 kJ/mol, shows the weakest Si-Si bonds of the three. This contributes to its reduced capacity for catenation. Nevertheless, germanium plays an important role in electronics, particularly in semiconductors, but it does not form natural extended chain compounds like carbon or even silicon. Thus, analyzing the bond energies gives insight into why carbon outshines both silicon and germanium in forming diverse and stable structures.