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

Question

The catenation tendency of \(\mathrm{C}, \mathrm{Si}\) and \(\mathrm{Ge}\) 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

Option (a) 348, 180, 167 is correct based on bond energies.

Step 1: Understand Catenation

Catenation is the ability of an element to form bonds with itself, creating chains or rings. Elements like carbon, silicon, and germanium are known for this property to varying degrees.

Step 2: Consider Bond Energies

The tendency to catenate relies largely on bond energies between identical atoms. Stronger bonds (higher bond energies) mean better catenation abilities.

Step 3: Rank Catenation Tendency

Given the order of catenation tendency: Ge < Si < C, carbon has the greatest tendency for catenation, followed by silicon and germanium.

Step 4: Analyze Bond Energies

The bond energy should be highest for carbon-carbon bonds as carbon has the strongest catenation tendency, followed by silicon and finally germanium. Thus, the bond energies should decrease in the order C-C, Si-Si, Ge-Ge.

Step 5: Match Bond Energies with Bonds

With bond energies provided as 348 kJ/mol, 180 kJ/mol, and 167 kJ/mol, match them to the respective C-C, Si-Si, and Ge-Ge bonds according to the decreasing order of catenation tendency observed. Hence, bond energies will align as: C-C (348), Si-Si (180), Ge-Ge (167).

Step 6: Identify the Correct Answer Choice

Compare the matched bond energies with the options given. Option (a) 348, 180, 167 corresponds correctly to the decreasing catenation tendency of C-Si-Ge.

Key Concepts

Bond Energy

Bond energy is the measure of bond strength in a chemical bond. It represents the amount of energy required to break one mole of bonds in a gaseous state. This energy is indicative of the stability and strength of the bond between two atoms. In simple terms, higher bond energy means the bond between the atoms is stronger and requires more energy to break.
Understanding bond energy is crucial when comparing the reactivity and stability of different elements. For example, carbon-carbon bonds generally have high bond energies, which leads to strong catenation tendencies. This means carbon atoms can form long, stable chains. Similarly, analyzing other elements like silicon and germanium also involves looking at their bond energies to predict their behavior in forming chains or networks.

C-C Bond

The carbon-carbon bond (-Cond) is a single bond found between carbon atoms. Carbon is unique due to its small size and ability to form four covalent bonds, making it ideal for catenation. The C-C bond has a high bond energy of approximately 348 kJ/mol. This high bond energy is a key reason for carbon's strength in forming stable and complex structures like organic molecules.
Students can think of C-C bonds as the building blocks of organic chemistry. They are responsible for the vast array of organic compounds. The strong bonds mean these molecules can be stable and versatile, leading to carbon's ubiquity in biological organisms and many industrial compounds.

Si-Si Bond

Silicon-silicon bonds (Si-Siond) occur between silicon atoms and play a significant role in the chemistry of silicon compounds. While silicon also exhibits catenation, it is less pronounced than in carbon due to its larger atomic size and lower bond energy of around 180 kJ/mol.
Silicon's ability to form chains is limited but significant in materials science. For example, silicon forms the backbone of many silicon-based polymers known as silicones. These materials are crucial in numerous applications, from electronics to cosmetics, showing the importance of understanding Si-Si bonds. Despite the weaker bond energy compared to carbon, silicon's bonds are still critical for forming essential materials.

Ge-Ge Bond

Germanium-germanium bonds (Ge-Geond) are similar in structure to both C-C and Si-Si bonds but with some distinctive differences. The bond energy of Ge-Ge bonds is around 167 kJ/mol, making them the weakest among the three discussed here.
This lower bond energy results in germanium's limited ability for catenation compared to carbon and silicon. While still able to form bonds with itself, germanium's weaker bonds restrict the length and complexity of chains. Nevertheless, Germanium is used in semiconductors and other electronics, highlighting the role this element plays despite its weaker bond energy.

Catenation Tendency

Catenation tendency describes the ability of an element to form chains or networks with itself by forming covalent bonds. The strength of this tendency depends largely on the bond energies involved. Stronger bonds lead to a higher catenation tendency.
In the sequence Ge < Si < C, carbon has the highest tendency for catenation due to its small size and high C-C bond energy. This makes carbon the backbone of organic chemistry, as it can form stable long chains. On the other hand, silicon and germanium have comparatively weaker Si-Si and Ge-Ge bonds. Thus, they have lower catenation tendencies, with germanium being the weakest. Despite this, both silicon and germanium are crucial in various industrial applications due to their specific properties.
Understanding these tendencies helps students predict how different elements will behave in forming complex structures and networks.