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

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

Step 1: Understanding Bond Polarity

Bond polarity arises from differences in electronegativity between two bonded atoms. The larger the difference in electronegativity, the more polar the bond is.

Step 2: Reviewing Electronegativity Values

Find the electronegativity values of the atoms involved: - Fluorine (F): 3.98 - Oxygen (O): 3.44 - Sulfur (S): 2.58 - Bromine (Br): 2.96 - Carbon (C): 2.55

Step 3: Calculating Electronegativity Differences

Calculate the difference in electronegativity for each pair: - \(|3.98 - 2.55| = 1.43\) for \(\mathrm{C}-\mathrm{F}\) - \(|3.44 - 2.55| = 0.89\) for \(\mathrm{C}-\mathrm{O}\) - \(|2.58 - 2.55| = 0.03\) for \(\mathrm{C}-\mathrm{S}\) - \(|2.96 - 2.55| = 0.41\) for \(\mathrm{C}-\mathrm{Br}\)

Step 4: Identifying the Most Polar Bond

The bond with the largest difference in electronegativity is the most polar. In this case, the \(\mathrm{C}-\mathrm{F}\) bond has the highest difference of 1.43, indicating it is the most polar.

Key Concepts

Electronegativity

Electronegativity is a fundamental concept in chemistry that describes an atom's ability to attract and hold onto electrons within a chemical bond. This concept aids in determining how electrons are distributed in a molecule. High electronegativity values mean that the atom strongly attracts electrons.
To understand it better, think of electronegativity as an indication of how "greedy" an atom is for electrons. Atoms with high electronegativity, like fluorine, which has a value of 3.98, tend to attract electrons more aggressively compared to atoms with lower values like carbon, which stands at 2.55.
Electronegativity values are important when analyzing chemical bonds. By looking at the differences in these values, we can predict whether a bond is more ionic or covalent in nature. The greater the difference, the more polar a bond potentially is.

Covalent Bonds

Covalent bonds are a type of chemical bond that involves the sharing of electron pairs between atoms. This type of bond forms when two atoms have a relatively small difference in electronegativity, allowing them to share electrons more or less equally.
Imagine covalent bonds as a handshake between atoms where they "agree" to share electrons. Unlike ionic bonds, where electrons can be transferred from one atom to another, covalent bonds imply a mutual sharing. This often happens between non-metal elements.
An everyday example of covalent bonds can be observed in water (\( ext{H}_2 ext{O} \)), where oxygen and hydrogen atoms share electrons to fill their respective outer electron shells. This bonding helps atoms attain a more stable energy state, often achieving a "fully filled" electron configuration.

Polar Bonds

Polar bonds are a subtype of covalent bonds marked by uneven sharing of electrons between two atoms. This phenomenon occurs when there is a significant difference in electronegativity between the two atoms. In polar bonds, one atom tends to pull the shared electrons closer to itself, creating a dipole moment.
To illustrate, consider the \( ext{C-F} \) bond in carbon-fluoride. Fluorine, being more electronegative, attracts the shared electrons more than carbon does. This results in an electron-rich fluorine end and an electron-poor carbon end, giving the bond its polar characteristic.

• If you think of a polar bond as a tug-of-war, one side (the more electronegative atom) pulls harder on the electron rope than the other.
• Such bonds are the reason behind many molecule interactions and properties, including solubility and boiling points.

Understanding polar bonds is essential for predicting how molecules will interact with each other in different contexts.