Question

Identify the most polar bond in each molecule. (a) \(\mathrm{HSCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (b) \(\mathrm{CHCl}_{2} \mathrm{~F}\) (c) \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\)

Short answer

Question: Identify the most polar bond in each molecule: (a) \(\mathrm{HSCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\), (b) \(\mathrm{CHCl}_{2} \mathrm{~F}\), (c) \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\). Answer: The most polar bonds in each molecule are: (a) O-H, (b) Cl-F, and (c) O-H.

Step-by-step solution

Determine the electronegativity values of the involved elements

We will start by looking up the electronegativity values of the elements involved in the molecules. For this exercise, we will use the Pauling scale of electronegativity, which assigns values between 0.7 and 3.98. - Hydrogen (H) has an electronegativity of 2.20 - Sulfur (S) has an electronegativity of 2.58 - Carbon (C) has an electronegativity of 2.55 - Oxygen (O) has an electronegativity of 3.44 - Chlorine (Cl) has an electronegativity of 3.16 - Fluorine (F) has an electronegativity of 3.98 - Nitrogen (N) has an electronegativity of 3.04 Now, we will analyze each molecule and identify the most polar bond.

Analyze molecule (a) \(\mathrm{HSCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\)

Calculate the electronegativity difference for the bonds: - H-S (2.20 - 2.58) = 0.38 - S-C (2.58 - 2.55) = 0.03 - C-C (2.55 - 2.55) = 0 - C-H (2.55 - 2.20) = 0.35 - C-O (2.55 - 3.44) = 0.89 - O-H (3.44 - 2.20) = 1.24 The O-H bond has the highest electronegativity difference and is the most polar bond in this molecule.

Analyze molecule (b) \(\mathrm{CHCl}_{2} \mathrm{~F}\)

Calculate the electronegativity difference for the bonds: - C-H (2.55 - 2.20) = 0.35 - C-Cl (2.55 - 3.16) = 0.61 - Cl-F (3.16 - 3.98) = 0.82 The Cl-F bond has the highest electronegativity difference and is the most polar bond in this molecule.

Analyze molecule (c) \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\)

Calculate the electronegativity difference for the bonds: - O-H (3.44 - 2.20) = 1.24 - C-O (2.55 - 3.44) = 0.89 - C-C (2.55 - 2.55) = 0 - C-H (2.55 - 2.20) = 0.35 - C-N (2.55 - 3.04) = 0.49 - N-H (3.04 - 2.20) = 0.84 The O-H bond has the highest electronegativity difference and is the most polar bond in this molecule. #Summary# - In molecule (a) \(\mathrm{HSCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\), the most polar bond is O-H. - In molecule (b) \(\mathrm{CHCl}_{2} \mathrm{~F}\), the most polar bond is Cl-F. - In molecule (c) \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\), the most polar bond is O-H.

Key concepts

Electronegativity

Electronegativity is a measure of how strongly an atom attracts the electrons in a chemical bond. Understanding this concept is essential when predicting the type of bond that will form between two atoms. When atoms with different electronegativities form a bond, the electrons are not shared equally. The more electronegative atom will pull the shared electrons closer to itself.

Electronegativity determines whether a bond will be nonpolar, polar, or ionic. In the context of our exercise, analyzing the difference in electronegativity values helps us gauge the polarity of the bond. If two atoms have similar electronegativity values, they share electrons equally and form a nonpolar bond. However, a significant difference in these values, typically greater than 0.5 on the Pauling scale, indicates the formation of a polar bond.

Polar Bonds

Polar bonds are the result of atoms with differing electronegativities coming together to form a molecule. These bonds have a distribution of charge across them, with one end being more negative (the end with the more electronegative atom) and the other more positive. Polar bonds are crucial in determining the physical properties of compounds, such as their solubility in water and their boiling and melting points.

In our exercise, identifying the polar bonds is important for comprehending the molecular structure and reactivity. For instance, the O-H and Cl-F bonds highlighted as most polar exhibit significant polarity due to the substantial differences in electronegativity between oxygen and hydrogen, and chlorine and fluorine respectively.

Pauling Scale

The Pauling scale is an index that quantifies the electronegativity of elements on a relative scale. Introduced by Linus Pauling, this scale typically ranges from 0.7 (for elements with the lowest electronegativity, such as francium) to 3.98 (for elements with the highest electronegativity, such as fluorine). The numerical values assigned make it convenient to compare electronegativities and anticipate the polarity of bonds.

For the given exercise, using the Pauling scale is vital in assessing which bonds are most polar. By looking at the differences in electronegativity values for various atom pairs, students can determine which bonds have the greatest difference and therefore which are more polar. This exercise serves as an excellent application of the Pauling scale to understand the behavior of different chemical species.