Problem 33 - Chemistry An Atoms First Approach

Question

Without using Fig. \(3-4,\) predict which bond in each of the following groups will be the most polar. a. \(C-F, S i-F, G e-F\) b. \(P-C\) or \(S-C\) \(\mathbf{c} . \mathbf{S}-\mathbf{F}, \mathbf{S}-\mathbf{C} \mathbf{l}, \mathbf{S}-\mathbf{B r}\) d. \(\mathrm{Ti}-\mathrm{Cl}, \mathrm{Si}-\mathrm{Cl}, \mathrm{Ge}-\mathrm{Cl}\)

Step-by-Step Solution

Answer

The most polar bonds for each group are: a. Si-F b. P-C c. S-F d. Ti-Cl

Step 1: Group a: C-F, Si-F, Ge-F

To determine the most polar bond, compare the difference in electronegativity for each bond: 1. C-F: Electronegativity of C = 2.55, Electronegativity of F = 3.98, Difference = \(|3.98-2.55|\) = 1.43. 2. Si-F: Electronegativity of Si = 1.90, Electronegativity of F = 3.98, Difference = \(|3.98-1.90|\) = 2.08. 3. Ge-F: Electronegativity of Ge = 2.01, Electronegativity of F = 3.98, Difference = \(|3.98-2.01|\) = 1.97. Since Si-F has the greatest difference in electronegativity, the most polar bond is Si-F.

Step 2: Group b: P-C, S-C

Compare the difference in electronegativity for each bond: 1. P-C: Electronegativity of P = 2.19, Electronegativity of C = 2.55, Difference = \(|2.55-2.19|\) = 0.36. 2. S-C: Electronegativity of S = 2.58, Electronegativity of C = 2.55, Difference = \(|2.58-2.55|\) = 0.03. Since P-C has the greater difference in electronegativity, the most polar bond is P-C.

Step 3: Group c: S-F, S-Cl, S-Br

Compare the difference in electronegativity for each bond: 1. S-F: Electronegativity of S = 2.58, Electronegativity of F = 3.98, Difference = \(|3.98-2.58|\) = 1.40. 2. S-Cl: Electronegativity of S = 2.58, Electronegativity of Cl = 3.16, Difference = \(|3.16-2.58|\) = 0.58. 3. S-Br: Electronegativity of S = 2.58, Electronegativity of Br = 2.96, Difference = \(|2.96-2.58|\) = 0.38. Since S-F has the greatest difference in electronegativity, the most polar bond is S-F.

Step 4: Group d: Ti-Cl, Si-Cl, Ge-Cl

Compare the difference in electronegativity for each bond: 1. Ti-Cl: Electronegativity of Ti = 1.54, Electronegativity of Cl = 3.16, Difference = \(|3.16-1.54|\) = 1.62. 2. Si-Cl: Electronegativity of Si = 1.90, Electronegativity of Cl = 3.16, Difference = \(|3.16-1.90|\) = 1.26. 3. Ge-Cl: Electronegativity of Ge = 2.01, Electronegativity of Cl = 3.16, Difference = \(|3.16-2.01|\) = 1.15. Since Ti-Cl has the greatest difference in electronegativity, the most polar bond is Ti-Cl.

Key Concepts

Polar Bonds

Polar bonds occur when there is an unequal sharing of electrons between two atoms in a chemical bond. This happens because one atom attracts the bonding electrons more strongly than the other. This unequal sharing results in a partial positive charge on one atom and a partial negative charge on the other, creating a dipole with a positive end and a negative end.
For example, consider the bond between hydrogen and chlorine in hydrochloric acid (HCl). Chlorine, being more electronegative, will pull the shared electrons towards itself more strongly than hydrogen. As a result, the chlorine end of the bond becomes slightly negative, while the hydrogen end becomes slightly positive. This is a classic example of a polar bond.
Understanding polar bonds is crucial because they can significantly influence the physical properties of molecules, such as boiling point and solubility, as well as their interactions with other molecules.

Difference in Electronegativity

The difference in electronegativity between two atoms is key to determining if a bond is polar. Electronegativity is a measure of how strongly an atom attracts electrons towards itself. The greater the difference in electronegativity between two atoms, the more polar the bond they form.
To calculate the difference in electronegativity, you simply subtract the electronegativity value of one atom from the other. For instance, if fluorine has an electronegativity of 3.98 and hydrogen 2.20, the difference is \(|3.98 - 2.20| = 1.78\). This large difference indicates a polar bond.

• Small differences (less than 0.5) suggest a nonpolar bond.
• Moderate differences (between 0.5 and 1.9) suggest a polar bond.
• Large differences (greater than 1.9) can lead to ionic bonding.

Recognizing this difference helps predict molecular behavior, as more polar bonds often lead to polar molecules, which can dissolve in water and participate in hydrogen bonding.

Bond Comparison

Bond comparison involves analyzing different chemical bonds to determine their relative polarity. By comparing the electronegativity differences, we can determine which bond is more polar compared to others.
Let's consider a set of bonds such as Si-F, C-F, and Ge-F. By calculating the differences in electronegativity:
- Si-F: \(3.98 - 1.90 = 2.08\)
- C-F: \(3.98 - 2.55 = 1.43\)
- Ge-F: \(3.98 - 2.01 = 1.97\)
From these calculations, Si-F has the highest electronegativity difference, making it the most polar bond among the group.

• Higher electronegativity differences signal more polar bonds.
• Comparing bonds helps in predicting chemical reactivity and interaction potential.

Bond comparison is an essential skill for understanding molecular structure and property predictions.

Chemical Bonds

Chemical bonds are the forces holding atoms together in molecules and compounds. These bonds are essential for the structure and function of all kinds of matter.
There are several different types of chemical bonds, the most common being:

• Covalent Bonds: where electrons are shared between atoms.
• Ionic Bonds: where electrons are transferred from one atom to another, creating ions.
• Metallic Bonds: where electrons are shared among a lattice of metal atoms.

Each type of bond has distinct characteristics that influence the properties of substances. Covalent bonds can be further classified based on polarity, such as polar and nonpolar covalent bonds. Understanding chemical bonds is foundational to studying chemistry, as it helps in explaining how substances interact, combine, and change. It reveals the underlying framework that supports all chemical reactions and formations in the universe.