Question

Amongst \(\mathrm{LiCl}, \mathrm{RbCl}, \mathrm{BcCl}_{2}\) and \(\mathrm{MgCl}_{2}\) the compounds with the greatest and least ionic character respectively arc (1) \(\mathrm{LiCl}\) and \(\mathrm{RbC} 1\) (2) \(\mathrm{RbCl}\) and \(\mathrm{BeCl}_{2}\) (3) \(\mathrm{RbC} 1\) and \(\mathrm{MgCl}_{2}\) (4) \(\mathrm{MgC}_{2}\) and \(\mathrm{BeCl}_{2}\)

Short answer

(2) \(\mathrm{RbCl}\) and \(\mathrm{BeCl_{2}}\)

Step-by-step solution

- Understanding Ionic Character

Ionic character in a compound depends on the difference in electronegativity between the elements. The greater the difference, the more ionic the bond is. Therefore, we need to compare the electronegativity values of the elements involved in \(\mathrm{LiCl}\), \(\mathrm{RbCl}\), \(\mathrm{BeCl_{2}}\), and \(\mathrm{MgCl_{2}}\).

- Electronegativity Values

The electronegativity values are approximately: \(\mathrm{Li} = 1.0\), \(\mathrm{Rb} = 0.8\), \(\mathrm{Be} = 1.5\), \(\mathrm{Mg} = 1.2\), and \(\mathrm{Cl} = 3.0\). Calculate the electronegativity differences with chlorine: \begin{align*} \mathrm{LiCl} & : |3.0-1.0| = 2.0 \ \mathrm{RbCl} & : |3.0-0.8| = 2.2 \ \mathrm{BeCl_{2}} & : |3.0-1.5| = 1.5 \ \mathrm{MgCl_{2}} & : |3.0-1.2| = 1.8 \end{align*}

- Identifying Greatest and Least Ionic Character

The compound with the greatest electronegativity difference has the greatest ionic character, while the one with the smallest difference has the least ionic character. From our calculations, \(\mathrm{RbCl}\) has the greatest difference (2.2) and \(\mathrm{BeCl_{2}}\) has the smallest difference (1.5).

- Conclusion

Based on the electronegativity differences, \(\mathrm{RbCl}\) has the greatest ionic character and \(\mathrm{BeCl_{2}}\) has the least ionic character.

Key concepts

electronegativity difference

Electronegativity difference plays a crucial role in determining the ionic character of a compound. Electronegativity is a measure of how strongly an atom attracts electrons in a bond. When two atoms with different electronegativity values form a bond, the electron pair is more attracted to the atom with higher electronegativity. This causes a partial charge separation, making the bond more ionic. The greater the difference in electronegativity between two bonded atoms, the more ionic the bond will be.
For example, in \(\text{LiCl}\), the electronegativity difference between lithium (1.0) and chlorine (3.0) is \( |3.0-1.0| = 2.0 \). This indicates a significant ionic character. Similarly, for \(\text{RbCl}\), the difference is \( |3.0-0.8| = 2.2 \), showing an even higher ionic character.

ionic bond

An ionic bond is formed when one atom completely transfers an electron to another atom, resulting in two ions with opposite charges. These ions attract each other and form a strong bond. This usually happens between metals and nonmetals because metals tend to lose electrons easily (forming positive ions), while nonmetals tend to gain electrons (forming negative ions).
Ionic bonds are characterized by high melting and boiling points, as well as the ability to conduct electricity when dissolved in water. In the context of our exercise, the ionic bond in \(\text{RbCl}\) is stronger and more ionic than in \(\text{BeCl}_2\) due to the larger electronegativity difference. Therefore, \(\text{RbCl}\) exhibits a greater ionic character.

compound comparison

When comparing compounds like \(\text{LiCl}\), \(\text{RbCl}\), \(\text{BeCl}_2\), and \(\text{MgCl}_2\), we need to look at their respective electronegativity differences to determine their ionic character. Based on the electronegativity values:

• Li (1.0) and Cl (3.0): \( 2.0 \)
• Rb (0.8) and Cl (3.0): \( 2.2 \)
• Be (1.5) and Cl (3.0): \( 1.5 \)
• Mg (1.2) and Cl (3.0): \( 1.8 \)

Among these compounds, \(\text{RbCl}\) has the highest electronegativity difference and thus the greatest ionic character. On the other hand, \(\text{BeCl}_2\) has the smallest difference, leading to the least ionic character. This comparison shows how the nature of bonds can vary greatly among compounds even within the same group.

chemical properties

The chemical properties of a compound, such as boiling point, melting point, solubility, and electrical conductivity, are deeply influenced by the type of bond it possesses—ionic or covalent. Compounds with higher ionic character, like \(\text{RbCl}\), typically have higher melting and boiling points because of the strong electrostatic forces between ions. They are usually solid at room temperature and dissolve well in water, conducting electricity in aqueous solutions.
In contrast, compounds with lesser ionic character, such as \(\text{BeCl}_2\), might exhibit properties that are somewhat between ionic and covalent compounds. While they might still dissolve in water, their melting and boiling points might be lower, and their electrical conductivity may be less compared to more ionic compounds. Understanding these chemical properties is essential for predicting how a substance will behave in different conditions, which is a key aspect of chemistry.