Problem 120 - Chemistry Matter and Change

Question

Rank the bonds according to increasing polarity. $$\begin{array}{ll}{\text { a. } \mathrm{C}-\mathrm{H}} & {\text { d. } \mathrm{O}-\mathrm{H}} \\ {\text { b. } \mathrm{N}-\mathrm{H}} & {\text { e. } \mathrm{Cl}-\mathrm{H}} \\ {\text { c. } \mathrm{Si}-\mathrm{H}} & {\text { e. } \mathrm{Cl}-\mathrm{H}}\end{array}$$

Step-by-Step Solution

Answer

The bonds ranked by increasing polarity are: Si-H, C-H, N-H, Cl-H, O-H.

Step 1: Understand Bond Polarity

Polarity in a bond is determined by the difference in electronegativity between the two atoms forming the bond. The greater the difference in electronegativity, the more polar the bond is. We need to compare these differences for each bond: \( \mathrm{C}-\mathrm{H} \), \( \mathrm{N}-\mathrm{H} \), \( \mathrm{Si}-\mathrm{H} \), \( \mathrm{O}-\mathrm{H} \), and \( \mathrm{Cl}-\mathrm{H} \).

Step 2: Determine Electronegativity Values

Look up the electronegativity values of the elements involved: Carbon (C) is 2.55, Nitrogen (N) is 3.04, Silicon (Si) is 1.90, Oxygen (O) is 3.44, Chlorine (Cl) is 3.16, and Hydrogen (H) is 2.20.

Step 3: Calculate Electronegativity Differences

For each bond, calculate the electronegativity difference: \( \mathrm{C}-\mathrm{H} (2.55-2.20=0.35) \), \( \mathrm{N}-\mathrm{H} (3.04-2.20=0.84) \), \( \mathrm{Si}-\mathrm{H} (1.90-2.20=0.30) \), \( \mathrm{O}-\mathrm{H} (3.44-2.20=1.24) \), \( \mathrm{Cl}-\mathrm{H} (3.16-2.20=0.96) \).

Step 4: Rank Bonds by Increasing Polarity

Using the calculated differences, rank the bonds from smallest to largest difference: \( \mathrm{Si}-\mathrm{H} (0.30) < \mathrm{C}-\mathrm{H} (0.35) < \mathrm{N}-\mathrm{H} (0.84) < \mathrm{Cl}-\mathrm{H} (0.96) < \mathrm{O}-\mathrm{H} (1.24) \).

Key Concepts

Electronegativity

Electronegativity is a crucial concept in chemistry. It describes the tendency of an atom to attract electrons towards itself when it forms a chemical bond. Each element has its unique electronegativity value, which helps us determine how atoms will interact with each other.

To understand bond polarity, we look at the electronegativity values of the atoms involved in the bond. If there is a large difference in their electronegativities, the bond will be polar, meaning the electrons are not shared equally.

For example, in a bond between Oxygen (O) and Hydrogen (H), the electronegativity difference is significant because oxygen strongly attracts electrons than hydrogen does.

Chemical Bonding

Chemical bonding is the force that holds atoms together in molecules. There are several types of chemical bonds, but when it comes to bond polarity, we often talk about covalent bonds.

Covalent bonds occur when atoms share electrons. However, if the atoms involved have different electronegativities, the shared electrons will spend more time closer to one atom. This results in a polar covalent bond.

For example, consider a bond between Nitrogen (N) and Hydrogen (H). Since nitrogen is more electronegative than hydrogen, the electrons are more attracted to the nitrogen, creating a polar bond with a slight charge difference at each end.

Molecular Polarity

Molecular polarity is what determines whether a molecule will be polar or nonpolar. A molecule is polar if it has a positive end and a negative end. This happens when there is an uneven distribution of electrons across the molecule.

For instance, water (\( H_2O \)) is a polar molecule due to its bent shape and the polarity of the oxygen-hydrogen bonds. The oxygen attracts more electrons, creating a partial negative charge, while the hydrogens have a partial positive charge.

• Polarity affects physical properties such as boiling point and solubility.
• Polar molecules generally dissolve well in water, a usual polar solvent.

Rank Bonds by Polarity

To rank bonds by polarity, we need to calculate the difference in electronegativity for each bond. The greater the difference, the more polar the bond is. Here's the list for the exercise provided:

- Silicon-Hydrogen (\( Si-H \)) with a small difference of 0.30 is the least polar.- Carbon-Hydrogen (\( C-H \)) follows, with a difference of 0.35.- Nitrogen-Hydrogen (\( N-H \)) is next, as they differ by 0.84.- Chlorine-Hydrogen (\( Cl-H \)) has a larger difference of 0.96.- Oxygen-Hydrogen (\( O-H \)) is the most polar, with a difference of 1.24.

Remember, ranking helps us predict and understand the behavior of molecules in different chemical reactions and environments.