Problem 85 - A Complete Resource Book in Chemistry for JEE Main

Question

Which element-element bond has the highest bond energy? (a) \(\mathrm{SiF}_{4}\) (b) Si-Si (c) \(\mathrm{Sn}-\mathrm{Sn}\) (d) Ge-Ge

Step-by-Step Solution

Answer

The Si-Si bond has the highest bond energy.

Step 1: Understanding Bond Energy

Bond energy is the measure of bond strength in a chemical bond, defined as the amount of energy required to break one mole of bonds in a substance. Generally, shorter bonds tend to have higher bond energies due to greater overlap of orbitals.

Step 2: Analyzing Molecular Structures

Examine each option to identify which involves single-element bonds. Options (b) Si-Si, (c) Sn-Sn, and (d) Ge-Ge involve single-element bonds, while (a) SiF extsubscript{4} involves Si-F bonds, which are not single-element bonds and not relevant to this comparison.

Step 3: Comparing Covalent Bonds

Si-Si, Sn-Sn, and Ge-Ge are all single bonds within the same group (group 14 elements). The elements increase in atomic size from Si to Sn, and as size increases, the bond length increases, generally leading to lower bond energy.

Step 4: Evaluating Experimental Data

Based on experimental data, bond energy decreases as the size of the atom increases. Thus, Si-Si bonds have higher bond energy than Sn-Sn and Ge-Ge bonds, as Si atoms are smaller with greater overlap.

Key Concepts

Chemical Bond Strength

Bond energy is a fundamental concept that helps us understand how tightly atoms are held together in a chemical bond. It tells us how much energy is required to break apart these bonds in a mole of the compound. The higher the bond energy, the stronger the bond. Typically:

• Bonds that are harder to break require more energy and thus have higher bond energies.
• Shorter bonds, which are usually stronger, have higher bond energies due to better overlap of orbitals between atoms.

In our specific exercise, we are looking at element-element bonds, primarily focused on single covalent bonds. In such bonds, if all other conditions are equal, the one with the highest bond energy will be the strongest. Comparing bond energies can give us crucial insights into the chemical reactivity and stability of different compounds.

Covalent Bonds

Covalent bonds form when two atomic nuclei share a pair of electrons. This sharing creates a powerful interaction that holds the atoms together. Here are a few key points:

• Covalent bonds are especially common between non-metal elements.
• The strength of these bonds is also influenced by how many pairs of electrons are shared; single, double, or triple bonds.
• Single-element bonds, like Si-Si or Sn-Sn, involve sharing electrons equally between identical atoms.

In this exercise, we compare bonds in group 14 elements such as Silicon-Silicon (Si-Si) and Tin-Tin (Sn-Sn). Bonds like Si-Si are significant since they set a benchmark in evaluating how atoms of the same element bond together and what factors could potentially alter their strength.

Atomic Size and Bond Length

Atomic size plays a significant role in determining the bond length between two atoms. Here is what you need to know:

• As atom size increases, the bond length typically increases, leading to a weaker bond.
• This is because larger atoms have more diffuse electron clouds with reduced overlap between orbitals.
• Smaller atoms, like Si compared to Sn or Ge, offer stronger interactions due to better orbital overlap.

Our exercise focuses on how these factors affect the bond energy of Si-Si, Sn-Sn, and Ge-Ge bonds. Silicon (Si) being the smallest among these atoms, forms the shortest and thus the strongest bond with high bond energy. This gives us a clear trend that as atomic size increases further down the group, bond length increases, resulting in a reduction in bond energy.