Problem 184 - Introductory Chemistry Atoms First

Question

Using only the periodic table, determine which bond in each pair is more ionic: (a) \(\mathrm{H}-\mathrm{F}\) or \(\mathrm{H}-\mathrm{Cl}\) (b) \(\mathrm{O}-\mathrm{F}\) or \(\mathrm{C}-\mathrm{F}\)

Step-by-Step Solution

Answer

(a) The \(\mathrm{H}-\mathrm{F}\) bond is more ionic, with an electronegativity difference of 1.88 compared to 1.06 for \(\mathrm{H}-\mathrm{Cl}\). (b) The \(\mathrm{C}-\mathrm{F}\) bond is more ionic, with an electronegativity difference of 1.43 compared to 0.54 for \(\mathrm{O}-\mathrm{F}\).

Step 1: Determine electronegativity values from the periodic table

Using the periodic table, we look up the electronegativity values for H, F, Cl, O, and C: - H (Hydrogen) has an electronegativity value of 2.1 - F (Fluorine) has an electronegativity value of 3.98 - Cl (Chlorine) has an electronegativity value of 3.16 - O (Oxygen) has an electronegativity value of 3.44 - C (Carbon) has an electronegativity value of 2.55

Step 2: Calculate the electronegativity differences for each bond pair

Now, we will compute the electronegativity difference for each bond pair: (a) H-F and H-Cl - H-F: 3.98 - 2.1 = 1.88 - H-Cl: 3.16 - 2.1 = 1.06 (b) O-F and C-F - O-F: 3.98 - 3.44 = 0.54 - C-F: 3.98 - 2.55 = 1.43

Step 3: Determine which bond is more ionic in each pair

Now that we have the electronegativity differences calculated, we can identify the more ionic bond in each pair: (a) H-F or H-Cl As the electronegativity difference between H and F (1.88) is greater than the electronegativity difference between H and Cl (1.06), the H-F bond is more ionic. (b) O-F or C-F Since the electronegativity difference between O and F (0.54) is less than the electronegativity difference between C and F (1.43), the C-F bond is more ionic. So, the final answer is: (a) The \(\mathrm{H}-\mathrm{F}\) bond is more ionic. (b) The \(\mathrm{C}-\mathrm{F}\) bond is more ionic.

Key Concepts

Electronegativity

Electronegativity is a fundamental concept in chemistry that helps us to understand how atoms interact with each other.
It is defined as the tendency of an atom to attract a bonding pair of electrons. The higher the electronegativity of an atom, the more it attracts electrons towards itself when forming a bond.

In the exercise, we used electronegativity values to determine which bonds were more ionic. This is because the greater the difference in electronegativity between two bonded atoms, the more ionic character that bond will have.
For instance:

• The H-F bond has a high electronegativity difference of 1.88, making it more ionic.
• A smaller difference like in the O-F bond (0.54) indicates less ionic character in comparison to something like C-F (1.43).

Electronegativity values are typically found using the periodic table, which offers a quick and useful guide for analyzing and predicting the behavior of atoms in molecules.

Periodic Table

The periodic table is not just a chart to memorize elements; it is a tool that organizes information in a way that is extremely useful for understanding atomic properties.
It helps easily find electronegativity values, among other things, which are crucial for predicting how atoms will interact in chemical bonds.

Each element on the periodic table is placed in a manner that highlights recurring chemical properties, and electronegativity is one of these important characteristics. Elements in the same group, or column, often show trends in their behavior.

For example:

• As you move across a period from left to right, electronegativity generally increases.
• As you move down a group, electronegativity tends to decrease.

Using the periodic table, we can quickly identify and compare the electronegativity of various elements, which aids in understanding the nature of chemical bonds and the structure of molecules.

Chemical Bonds

Chemical bonds are the connections between atoms in a molecule. They form as a result of atoms sharing or transferring electrons.
Ionic bonds, specifically, form when one atom donates an electron to another, resulting in a bond between ions with opposite charges. This type of bond is generally strong and results from large differences in electronegativity.

In the exercise, the bonds such as H-F and C-F are evaluated based on how ionic they are.
The more significant the difference in electronegativity between the two atoms in the bond:

• The more ionic character the bond will possess.
• The more likely the bond is to result in a strong ionic connection.

Understanding chemical bonds and their character is essential to many areas of chemistry, from predicting reaction outcomes to designing new materials with specific properties.