Problem 119 - Chemistry Matter and Change

Question

Predict which bond is the most polar $$\begin{array}{ll}{\text { a. } C-O} & {\text { c. } C-C l} \\ {\text { b. } S i-O} & {\text { d. } C-B r}\end{array}$$

Step-by-Step Solution

Answer

Si-O bond is the most polar with an electronegativity difference of 1.54.

Step 1: Understanding Polarity

Polarity is determined by the difference in electronegativity between two atoms. The greater the difference, the more polar the bond.

Step 2: Look Up Electronegativity Values

Consult the periodic table for electronegativity values: Carbon (C) is 2.55, Oxygen (O) is 3.44, Silicon (Si) is 1.90, Chlorine (Cl) is 3.16, and Bromine (Br) is 2.96.

Step 3: Calculate Electronegativity Differences

For bond a (C-O): \[3.44 - 2.55 = 0.89\]For bond b (Si-O): \[3.44 - 1.90 = 1.54\]For bond c (C-Cl): \[3.16 - 2.55 = 0.61\]For bond d (C-Br): \[2.96 - 2.55 = 0.41\]

Step 4: Compare the Differences

Among the calculated electronegativity differences, bond b (Si-O) has the largest difference at 1.54, indicating the highest polarity among the given options.

Key Concepts

Electronegativity

Electronegativity is a key concept in chemistry essential for understanding how atoms interact with one another. It refers to the tendency of an atom to attract shared electrons within a covalent bond. The more electronegative an atom, the stronger its pull on electrons.
Electronegativity values are typically assigned based on a scale developed by Linus Pauling, with fluorine being the most electronegative element at 3.98. Other elements are compared to fluorine to determine their ability to attract electrons.

• Atoms with higher electronegativity, like oxygen and fluorine, tend to pull electrons towards themselves more strongly.
• Atoms with lower electronegativity, like sodium and potassium, have less pull on electrons.

Understanding electronegativity helps predict chemical bond polarity, the nature of chemical reactions, and how molecules interact with each other. In general, the greater the difference in electronegativity between two bonded atoms, the more polar the bond will be.

Periodic Table

The periodic table is a powerful tool that organizes the chemical elements based on their atomic number, electron configurations, and recurring chemical properties. It is also instrumental in predicting the behaviors of elements, including electronegativity values.

• As you move from left to right across a period, electronegativity values generally increase. This means elements on the right side of the table are usually more electronegative than those on the left.
• Conversely, as you move down a group, the electronegativity values decrease. This is why elements lower in a group, such as bromine, are less electronegative compared to elements higher up, like chlorine.

The periodic table thus provides a quick reference guide to assess how likely an atom is to attract electrons based on its position. This knowledge forms the foundation for understanding bond polarity and molecular interactions.

Polar Covalent Bonds

Polar covalent bonds arise when two atoms with different electronegativities share electrons. When this happens, the shared electrons are pulled closer toward the more electronegative atom, creating a dipole moment characterized by a partial charge distribution across the molecule.

• If the electronegativity difference between two atoms is significant but not enough to transfer electrons completely, a polar covalent bond forms. This is the case in water (\( \text{H}_2\text{O} \)), where oxygen’s higher electronegativity pulls electrons away from hydrogen.
• In contrast, if the electronegativity difference is very small, the bond is non-polar covalent, as seen in molecules like nitrogen gas (\( \text{N}_2 \)), where there is little to no charge separation.

In the context of the exercise, the Si-O bond, with the largest electronegativity difference of 1.54, exemplifies a highly polar covalent bond. The larger this difference, the more polar and asymmetric a bond's electron distribution becomes, impacting the molecule's physical and chemical properties.