Problem 120 - Chemistry Matter and Change

Question

Rank the bonds according to increasing polarity. $$ \begin{array}{l}{\text { a. } C-H} \\ {\text { b. } N-H} \\ {\text { c. } S i-H}\\\\{\text { d. } O-H} \\ {\text { e. } C l-H}\end{array} $$

Step-by-Step Solution

Answer

The final ranking of the bonds according to increasing polarity is: \(Si-H < C-H < N-H < Cl-H < O-H\)

Step 1: Calculate electronegativity difference

We will start by finding the electronegativity difference for the given bonds. Electronegativity values: C: 2.55, H: 2.20, N: 3.04, Si: 1.90, O: 3.44, Cl: 3.16 a. C-H: |2.55 - 2.20| = 0.35 b. N-H: |3.04 - 2.20| = 0.84 c. Si-H: |1.90 - 2.20| = 0.30 d. O-H: |3.44 - 2.20| = 1.24 e. Cl-H: |3.16 - 2.20| = 0.96

Step 2: Sort bonds

Now, let's sort them in increasing order of their electronegativity differences. 1. Si-H: 0.30 2. C-H: 0.35 3. N-H: 0.84 4. Cl-H: 0.96 5. O-H: 1.24

Step 3: Final ranking

Thus, the final ranking of the bonds according to increasing polarity is: \(Si-H < C-H < N-H < Cl-H < O-H\)

Key Concepts

Electronegativity

Electronegativity is a molecule's ability to attract and hold on to electrons in a chemical bond. It's like a tug-of-war where the more electronegative atom pulls harder on the shared electrons. Each element has a specific electronegativity value, and these can vary widely across the periodic table.

The higher an element's electronegativity, the stronger its ability to attract electrons. For example, fluorine is the most electronegative element, making it excellent at "grabbing" electrons from other atoms. In the given exercise, we see this trait in action as we calculate the difference in electronegativity between hydrogen (H) and other elements like carbon (C), nitrogen (N), silicon (Si), oxygen (O), and chlorine (Cl).

When determining the polarity of a bond, we subtract the electronegativity values of the bonded atoms. The greater the difference, the more polar the bond. For instance, the O-H bond has a high electronegativity difference of 1.24, resulting in a highly polar bond.

Covalent Bonds

Covalent bonds occur when two atoms share electrons. Instead of transferring electrons as in ionic bonds, the atoms share to achieve a full outer shell, reaching a more stable state. This type of bonding happens mostly between nonmetal atoms.

The shared electrons "belong" to both atoms, which creates a bond holding them together. Despite their commonality, covalent bonds differ in strength and properties based on the involved atoms' electronegativity.

• Strong covalent bonds usually have very little influence from electronegativity differences.
• Weak covalent bonds often result when there is a significant electronegativity difference between the atoms, leading to polar bonds.

The single, double, and triple bonds in molecules illustrate different levels of electron sharing. For example, in the exercise, the O-H bond is often present in water, showing a common covalent bond that has characteristics of polarity due to the high electronegativity difference.

Polar and Nonpolar Bonds

Chemical bonds can be classified as either polar or nonpolar, based on how equally the electrons are shared between the two atoms. Learning to differentiate between these can greatly help understand molecular behavior.

• Polar Bonds: Occur when there is a notable difference in electronegativity between the two atoms. Electrons are shared unequally, causing a charge imbalance. We see examples of polar bonds in molecules like water (H-O bond), where the electrons are closer to oxygen due to its higher electronegativity.
• Nonpolar Bonds: These occur when two atoms have identical or very similar electronegativities. In such cases, the electrons are shared equally. A good example of this is found in molecules like diatomic nitrogen (N₂) or the C-H bond.

In our exercise, the polarity ranking is determined by electronegativity differences: the greater, the more polar the bond. For instance, O-H is more polar than Si-H, with Si-H being categorized as closer to nonpolar due to its minimal electronegativity difference.