Problem 41 - Chemistry: The Central Science

Question

Which of the following bonds are polar? (a) B-F, (b) \(\mathrm{Cl}-\mathrm{Cl}\), (c) Se-O, (d) H-I. Which is the more electronegative atom in each polar bond?

Step-by-Step Solution

Answer

Bonds (a) B-F, (c) Se-O, and (d) H-I are polar, while bond (b) Cl-Cl is nonpolar. The more electronegative atoms in each polar bond are F, O, and I, respectively.

Step 1: Determine electronegativity values

First, we need to find the electronegativity values for each of the atoms involved in the given bonds. We can use the periodic table or a reference table to do this. Here are the electronegativity values: - B (Boron) = 2.04 - F (Fluorine) = 3.98 - Cl (Chlorine) = 3.16 - Se (Selenium) = 2.55 - O (Oxygen) = 3.44 - H (Hydrogen) = 2.20 - I (Iodine) = 2.66

Step 2: Calculate electronegativity differences

Next, we will calculate the electronegativity differences for each bond by subtracting the smaller value from the larger value: - (a) B-F: \( |3.98 - 2.04| = 1.94 \) - (b) Cl-Cl: \( |3.16 - 3.16| = 0 \) - (c) Se-O: \( |3.44 - 2.55| = 0.89 \) - (d) H-I: \( |2.66 - 2.20| = 0.46 \)

Step 3: Identify polar bonds and more electronegative atom

Now, we will identify which bonds are polar based on the electronegativity differences and determine the more electronegative atom in each polar bond. - (a) B-F: The electronegativity difference is 1.94, which indicates a polar bond. F (Fluorine) is the more electronegative atom in this bond. - (b) Cl-Cl: The electronegativity difference is 0, which indicates a nonpolar bond. There is no more electronegative atom since both are the same element. - (c) Se-O: The electronegativity difference is 0.89, which indicates a polar bond. O (Oxygen) is the more electronegative atom in this bond. - (d) H-I: The electronegativity difference is 0.46, which indicates a polar bond. I (Iodine) is the more electronegative atom in this bond.

Step 4: Conclusion

Bonds (a) B-F, (c) Se-O, and (d) H-I are polar, while bond (b) Cl-Cl is nonpolar. The more electronegative atoms in each polar bond are F, O, and I, respectively.

Key Concepts

Electronegativity

Electronegativity is a fundamental concept in chemistry that describes the tendency of an atom to attract electrons in a chemical bond. It's a dimensionless quantity, usually measured on the Pauling scale, which was developed by chemist Linus Pauling. Atoms with higher electronegativity values will more strongly attract bonding electrons.

For example, in the exercise given, fluorine (F) has the highest electronegativity value (3.98), making it the most electron-attracting element in the bonds discussed. When comparing electronegativity values to determine if a bond is polar, as in the steps provided, a significant difference usually results in a polar bond. In general, a difference of 0.5 or more can lead to polarity, though this can vary.

Chemical Bonding

Chemical bonding is the force that holds atoms together in molecules. There are several types of bonds, including ionic, covalent, and metallic bonds. Ionic bonds form when there is a complete transfer of electrons from one atom to another, leading to the formation of oppositely charged ions. Covalent bonds occur when atoms share electrons, and the way they share electrons can lead to either nonpolar or polar covalent bonds.

In a polar covalent bond, one atom exerts a greater attraction for the electrons than the other, leading to an uneven distribution of charge. This is the case with the B-F, Se-O, and H-I bonds in the exercise. Conversely, in the Cl-Cl bond, the electrons are shared equally because both atoms have the same electronegativity, resulting in a nonpolar bond.

Molecular Polarity

Molecular polarity is determined by both the polarity of individual bonds and the shape of the molecule. A polar molecule has a net dipole moment, where one side of the molecule is slightly negative, and the opposite side is slightly positive. This occurs when polar bonds within a molecule are arranged asymmetrically.

Even if a molecule has polar bonds, like H-I, it may still be nonpolar if the molecule's geometry is symmetrical. Thus, knowing just the bond polarities isn't always enough to determine the overall polarity of the molecule. It's important to also consider molecular geometry when evaluating the polarity of a molecule, aiming for a comprehensive understanding of molecular polarity to predict the behavior of substances like solubility and reactivity.