Problem 182 - Introductory Chemistry Atoms First

Question

Arrange the following sets of bonds in order of increasing ionic character. Use the symbols \(\delta+\) and \(\delta-\) to indicate partial charges, if any, in the bonds: \(\mathrm{O}-\mathrm{Cl}, \mathrm{C}-\mathrm{F}, \mathrm{N}-\mathrm{Cl}, \mathrm{O}-\mathrm{H}, \mathrm{S}-\mathrm{O}\)

Step-by-Step Solution

Answer

The bonds in order of increasing ionic character are: N-Cl, O-Cl, S-O, O-H, C-F With partial charges assigned as: 1. N\(\delta+\)-Cl\(\delta-\) 2. O\(\delta-\)-Cl\(\delta+\) 3. S\(\delta+\)-O\(\delta-\) 4. O\(\delta-\)-H\(\delta+\) 5. C\(\delta+\)-F\(\delta-\)

Step 1: Electronegativities of the elements involved

First, we need to know the electronegativities of the elements involved in the given bonds, which can be found in a periodic table or related resources. I will provide the approximate electronegativities below: 1. Oxygen (O): 3.44 2. Chlorine (Cl): 3.16 3. Carbon (C): 2.55 4. Fluorine (F): 3.98 5. Nitrogen (N): 3.04 6. Hydrogen (H): 2.20 7. Sulfur (S): 2.58 Now we will calculate the electronegativity differences for each bond.

Step 2: Calculate electronegativity differences

1. O-Cl: \(\Delta EN = 3.44 - 3.16 = 0.28\) 2. C-F: \(\Delta EN = 3.98 - 2.55 = 1.43\) 3. N-Cl: \(\Delta EN = 3.16 - 3.04 = 0.12\) 4. O-H: \(\Delta EN = 3.44 - 2.20 = 1.24\) 5. S-O: \(\Delta EN = 3.44 - 2.58 = 0.86\)

Step 3: Arrange bonds in increasing order of ionic character

Here, higher electronegativity differences correspond to higher ionic characters. Thus, we can arrange these differences in increasing order: 1. N-Cl \(\Delta EN = 0.12\) 2. O-Cl \(\Delta EN = 0.28\) 3. S-O \(\Delta EN = 0.86\) 4. O-H \(\Delta EN = 1.24\) 5. C-F \(\Delta EN = 1.43\) Based on these values, the bonds in order of increasing ionic character are: N-Cl, O-Cl, S-O, O-H, C-F

Step 4: Assign partial charges to the bonds

Next, let's indicate the partial charges in the bonds using the symbols \(\delta+\) (partial positive charge) and \(\delta-\) (partial negative charge): 1. N-Cl: N\(\delta+\)-Cl\(\delta-\), as Cl is more electronegative than N 2. O-Cl: O\(\delta-\)-Cl\(\delta+\), as O is more electronegative than Cl 3. S-O: S\(\delta+\)-O\(\delta-\), as O is more electronegative than S 4. O-H: O\(\delta-\)-H\(\delta+\), as O is more electronegative than H 5. C-F: C\(\delta+\)-F\(\delta-\), as F is more electronegative than C

Key Concepts

Electronegativity

Electronegativity is a key concept when studying chemical bonds. Simply put, it is a measure of how strongly an atom can attract electrons in a chemical bond. Elements with high electronegativity, such as oxygen and fluorine, tend to attract electrons more readily.
To determine the ionic character of a bond, we look at the difference in electronegativity between the bonded atoms. Greater differences result in bonds with higher ionic character. For example, in the bonds given for the exercise, like C-F, the electronegativity difference is quite large (1.43). As a result, the bond is more ionic in nature.
Understanding electronegativity helps in predicting how atoms are going to interact in a compound, which is crucial for understanding the compound's properties.

Partial Charges

In covalent bonds, electrons are not always shared equally. When two different atoms form a bond, the more electronegative atom pulls the shared electrons closer to itself. This leads to partial charges:

• The more electronegative atom carries a partial negative charge, denoted as \(\delta -\).
• The less electronegative atom takes on a partial positive charge, denoted as \(\delta +\).

This concept is important because it explains how ionic character can be present even in otherwise covalent bonds. For instance, in the O-H bond, oxygen is more electronegative than hydrogen, so oxygen gets a \(\delta-\) charge while hydrogen gets a \(\delta+\) charge, contributing to the bond's polarity.

Bond Polarity

Bond polarity arises when there is an unequal sharing of electrons between two atoms in a bond. This happens due to the difference in their electronegativities.
The concept of polarity is crucial because it affects how molecules interact with each other. Polar bonds can form dipoles, which influence the molecule's overall interaction with other molecules. The greater the difference in electronegativity between the two atoms, the more polar the bond becomes.
In the exercise, the C-F bond is highly polar due to fluorine's high electronegativity compared to carbon. Polar molecules tend to exhibit unique properties, such as higher boiling points or the ability to dissolve in water, due to their charged nature.