Problem 60 - Chemistry The Science in Context

Question

In which of the following compounds is the bond between the atoms expected to have the most covalent character? \(\mathrm{AlCl}_{3} ; \mathrm{AlBr}_{3} ; \mathrm{AlI}_{3} ; \mathrm{GaF}_{3}\).

Step-by-Step Solution

Answer

Answer: The compound with the bond that has the most covalent character is AlI3.

Step 1: List Electronegativity Values

Look up the electronegativity values for the elements found in each of the compounds given: Aluminum (Al): 1.61 Chlorine (Cl): 3.16 Bromine (Br): 2.96 Iodine (I): 2.66 Gallium (Ga): 1.81 Fluorine (F): 3.98

Step 2: Calculate Electronegativity Differences

Calculate the difference in electronegativity values for each bond in the compounds: - \(\mathrm{AlCl}_{3}\) : |3.16 - 1.61| = 1.55 - \(\mathrm{AlBr}_{3}\) : |2.96 - 1.61| = 1.35 - \(\mathrm{AlI}_{3}\) : |2.66 - 1.61| = 1.05 - \(\mathrm{GaF}_{3}\) : |3.98 - 1.81| = 2.17

Step 3: Determine the Bond with the Most Covalent Character

Identify the bond with the smallest difference in electronegativity, as this bond will have the most covalent character: The bond with the smallest difference in electronegativity is the Al-I bond in \(\mathrm{AlI}_{3}\), with a difference of 1.05. Thus, the compound with the bond that has the most covalent character is \(\mathrm{AlI}_{3}\).

Key Concepts

Electronegativity Difference

Electronegativity is a chemical property that describes how strongly atoms attract bonding electrons to themselves. The electronegativity difference between two atoms is a strong indicator of the type of bond they will form. Generally, the larger the difference in electronegativity, the more polar the bond will be, exhibiting more ionic character. Conversely, a smaller difference indicates a bond that is less polar, and therefore more covalent.

When determining the character of the bond, it's important to simply calculate the absolute difference between the electronegativity values of the two elements involved. For example, in the exercise provided, \( \mathrm{AlI}_{3} \) has the smallest electronegativity difference and is therefore predicted to have the most covalent character among the given compounds.

Students can grasp this concept more effectively by visualizing electronegativity on the periodic table, where it generally increases from left to right and from bottom to top. It is also helpful to memorize or have a reference for common electronegativity values when comparing elements.

Chemical Bonding

Chemical bonding is the process by which atoms combine to form compounds. There are three primary types of chemical bonds: ionic, covalent, and metallic. Understanding the differences between these types of bonds is crucial to predicting the properties of compounds.

To determine the bonding type, you must consider factors such as electronegativity difference, as previously mentioned, and also the overall context, for example, whether the elements involved are metals, nonmetals, or a mixture of both.

Role of Electronegativity in Bonding

Electronegativity plays a key role in determining the type of bond formed: ionic bonds generally form between elements with a high electronegativity difference, while covalent bonds form between elements with similar electronegativities. The exercise on \( \mathrm{AlI}_{3} \) demonstrates this concept elegantly by showing a comparison between several pairs of elements and their resulting bond types.

Covalent Bonds

Covalent bonds are a type of chemical bonding where two atoms share one or more pairs of electrons. This bond forms when the elements involved have similar electronegativity values, as there is no dominant atom to take the electrons completely. Instead, the electrons are shared, allowing each atom to acquire a stable electron configuration.

Shared electron pairs are often referred to as 'bonding pairs' or 'shared pairs,' forming a stable molecule. Covalent bonding is found in many non-metallic elements and compounds, such as water (H2O), carbon dioxide (CO2), and methane (CH4).

The concept of covalent bonding is well-illustrated by looking at molecules with low electronegativity differences. In the Al-I bond within \( \mathrm{AlI}_{3} \) from our exercise, the small difference signifies that the electrons are more equally shared between the aluminum and iodine atoms, which is the hallmark of covalent character in a bond.