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) \(\mathrm{Si}-\mathrm{Si}\) (c) \(\mathrm{Sn}-\mathrm{Sn}\) (d) \(\mathrm{Ge}-\mathrm{Ge}\)

Step-by-Step Solution

Answer

The \\(Si-F\\) bond in \\(SiF_4\\) has the highest bond energy.

Step 1: Understand Bond Energy

Bond energy is the amount of energy required to break a bond between two atoms in a molecule. Higher bond energy means a stronger bond.

Step 2: Analyze the Given Compounds

Compare the types of bonds in the options. Option (a) involves bonds between silicon and fluorine, \( ext{Si-F}\), whereas options (b), (c), and (d) involve bonds between identical atoms: silicon-silicon \( ext{Si-Si}\), tin-tin \( ext{Sn-Sn}\), and germanium-germanium \( ext{Ge-Ge}\).

Step 3: Consider the \\(Si-Si\\) Bond

Generally, the bond energy of the \(Si-Si\) bond is lower than that of the \(Si-F\) bond due to larger atomic size and less effective overlap between orbitals.

Step 4: Evaluate the \\(Sn-Sn\\) and \\(Ge-Ge\\) Bonds

The \(Sn-Sn\) and \(Ge-Ge\) bonds are weaker than \(Si-Si\) because tin and germanium are larger atoms with even less effective overlap, leading to lower bond energy.

Step 5: Determine the Strongest Bond

The bond in \(SiF_4\) is actually a \(Si-F\) bond. Fluorine forms a very strong bond with silicon due to its high electronegativity. \(Si-F\) bonds have very high bond energy.

Key Concepts

Bond Energy

Let's dive into the concept of bond energy, an essential topic in understanding chemical bonding. Bond energy refers to the amount of energy required to break one mole of a bond in a molecule into its individual atoms. It's measured in kilojoules per mole (kJ/mol).

• The higher the bond energy, the stronger the bond. This means the atoms are held together more tightly, requiring more energy to separate them.
• Bond energy provides information about the stability of a molecule. Weak bonds have lower bond energies and are generally easier to break.
• Bond energies help predict molecular reactions, as strong bonds often mean stable molecules.

When comparing molecules, those with higher bond energies are less likely to undergo chemical reactions. This is because disrupting such strong bonds demands significant energy. Understanding bond energies helps chemists manipulate reactions and achieve desired outcomes.

Silicon-Fluorine Bond

The silicon-fluorine bond ( Si-F ) is known for its exceptional strength, making it highly significant in molecular chemistry. This strength derives from several factors:

• Fluorine's High Electronegativity: As the most electronegative element, fluorine pulls electrons strongly towards itself. This creates a polar bond with silicon, enhancing the bond's strength.
• Effective Overlap: The small size of fluorine allows for a better overlap of orbitals between silicon and fluorine.
• Covalent Nature: The Si-F bond is highly covalent and stable, gaining additional strength from the significant electronegative difference.

These properties result in exceptionally high bond energy, far exceeding many other common bonds. The robust nature of the Si-F bond makes it less reactive and sometimes difficult to break under normal conditions.

Electronegativity

Electronegativity is a measure of how strongly an atom attracts shared electrons in a chemical bond. It's a fundamental property in understanding molecular interactions:

• Electronegativity varies across the periodic table. It's higher in non-metals and increases across a period from left to right.
• Fluorine, the most electronegative element, can form strong, polar bonds due to its ability to attract electrons.
• The difference in electronegativity between two atoms in a bond dictates the bond's nature. Large differences often result in polar covalent bonds, while smaller differences typically lead to non-polar covalent bonds.

Electronegativity is crucial for predicting molecule behavior, reactivity, and bond strength. In silicon-fluorine bonds, the large electronegativity difference is key to the bond's strength and stability.

Molecular Chemistry

Molecular chemistry focuses on the study of molecules, which are compounds of two or more atoms bonded together. It covers the interaction, synthesis, and behavior of these molecules.

• Understanding chemical bonding is fundamental in molecular chemistry, as the nature of these bonds determines molecular properties and reactions.
• Silicon-fluorine bonds serve as an example of how atomic properties, like electronegativity, influence bond strength and chemical behavior.
• Molecular chemistry advances fields such as materials science, pharmaceuticals, and nanotechnology by manipulating molecular characteristics to achieve specific outcomes.

Grasping the principles of molecular chemistry enables scientists to develop new materials and processes, broadening the potential for innovation in numerous domains. The study of bond energies and electronegativity within this scope provides insight into molecular stability and reactivity.