Problem 27 - A Complete Resource Book in Chemistry for JEE Main

Question

The most polar covalent species among the ones listed is (a) \(\mathrm{C}-\mathrm{S}\) (b) \(\mathrm{C}-\mathrm{O}\) (c) \(\mathrm{C}-\mathrm{F}\) (d) \(\mathrm{C}-\mathrm{Br}\)

Step-by-Step Solution

Answer

(c) \(\mathrm{C}-\mathrm{F}\) is the most polar bond.

Step 1: Understanding Polarity

Polarity in covalent bonds is determined by the difference in electronegativity between the two atoms involved. The greater the difference, the more polar the bond.

Step 2: Determine Electronegativity Values

Identify the electronegativity of each element involved in the carbon compounds: - Carbon (C) has an electronegativity of 2.5. - Sulfur (S) has an electronegativity of 2.5. - Oxygen (O) has an electronegativity of 3.5. - Fluorine (F) has an electronegativity of 4.0. - Bromine (Br) has an electronegativity of 2.8.

Step 3: Calculate Electronegativity Differences

Calculate the difference in electronegativity for each bond:- \(\text{C-S}: 2.5 - 2.5 = 0\)- \(\text{C-O}: 3.5 - 2.5 = 1.0\)- \(\text{C-F}: 4.0 - 2.5 = 1.5\)- \(\text{C-Br}: 2.8 - 2.5 = 0.3\)

Step 4: Identify the Most Polar Bond

The bond with the highest electronegativity difference is the most polar. From the calculations:- \(\text{C-F}: 1.5\) This is the largest difference, hence, the C-F bond is the most polar.

Key Concepts

Covalent bonds

Covalent bonds are fundamental in chemistry, forming when two atoms share one or more pairs of electrons. This type of bond is crucial for creating molecules. Unlike ionic bonds, where electrons are transferred, in covalent bonds, the electrons are shared, allowing each atom to attain a stable electron configuration.
Atoms involved in covalent bonding can either share electrons equally or unequally. When sharing is equal, the bond is termed nonpolar covalent. However, when one atom pulls the shared electrons closer to itself, the bond becomes polar covalent, influenced by the atoms' electronegativity.
Electronegativity is a measure of an atom's ability to attract and hold onto electrons. Thus, understanding electronegativity is crucial in predicting whether a covalent bond will be polar or nonpolar.

Polarity

Polarity in molecules arises from differences in electronegativity between bonded atoms. When one atom attracts the bonding electrons more than the other, a dipole moment is created, resulting in a polar bond.
In the context of covalent bonds, polarity is determined by examining electronegativity differences. As noted in the exercise solution, a greater difference in electronegativity results in a more polar bond.
For example, the electronegativity difference in a carbon-fluorine (\[ ext{C-F}\]) bond is sizable, making it highly polar. The atom with the higher electronegativity will acquire a partial negative charge, while the other atom ends up with a partial positive charge.
This polar characteristic is essential as it influences the physical properties of the molecule, such as solubility and boiling points.

Chemical bonding

Chemical bonding is the force that holds atoms together, forming compounds and molecules. At its core, bonding involves interactions between electrons that dictate the structural and chemical properties of substances.
There are several types of chemical bonds, with covalent bonds being one of the most common in organic compounds. When atoms bond covalently, they share electrons to achieve stability, typically reaching a noble gas electron configuration.
The concept of electronegativity plays a key role in determining the nature of these bonds. Bonds can range from purely covalent to highly polar based on electronegativity differences. Chemical bonding not only determines whether a substance is stable but also its reactivity, as the arrangement and interactions of electrons influence chemical reactions.