Question

Which of the following is correct? (a) The rate of ionic reactions are very slow (b) The number of electrons present in the valence shell of \(\mathrm{S}\) in \(\mathrm{SF}_{6}\) is 12 (c) According to VSEPR theory \(\mathrm{SnCl}_{2}\) is a linear molecule (d) The correct order of stability to form ionic compoundsamong \(\mathrm{Na}^{+}, \mathrm{Mg}^{2+}\) and \(\mathrm{Al}^{3+}\) is \(\mathrm{Al}^{3+}>\mathrm{Mg}^{2+}\) \(>\mathrm{Na}^{+}\)

Short answer

Option (d) is correct.

Step-by-step solution

Analyzing Option (a)

The rate of ionic reactions is generally not slow. Ionic reactions involve transfer of electrons and typically occur faster in solutions with ions moving freely. Therefore, option (a) is incorrect.

Analyzing Option (b)

In the compound \( \mathrm{SF}_{6} \), sulfur forms six bonds with fluorine, but it only has six valence electrons utilized in bonding. The electrons in these bonds do not increase the sulfur's valence shell count beyond its initial six, so option (b) is incorrect.

Analyzing Option (c)

According to VSEPR theory, \( \mathrm{SnCl}_{2} \) has a lone pair of electrons, which results in a bent molecular geometry, not linear. Therefore, option (c) is incorrect.

Analyzing Option (d)

The stability of forming ionic compounds increases with the cation's charge and its ionic potential. \( \mathrm{Al}^{3+} \) has a higher charge and greater polarizing power compared to \( \mathrm{Mg}^{2+} \) and \( \mathrm{Na}^{+} \). Thus, the stability order \( \mathrm{Al}^{3+} > \mathrm{Mg}^{2+} > \mathrm{Na}^{+} \) is correct.

Key concepts

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom. These electrons play a crucial role in chemical bonding because they are the electrons involved in forming bonds with other atoms. In general, atoms will gain, lose, or share valence electrons in order to achieve a more stable electron configuration, often aiming for the same number of valence electrons as the nearest noble gas. The concept of valence electrons helps in predicting the types of bonds that an atom can form and the number of bonds that can be made. For example:

• In the compound \( \mathrm{SF}_{6} \), sulfur uses its six valence electrons to form bonds with six fluorine atoms.
• Each fluorine needs one electron to complete its octet, forming stable covalent bonds with sulfur.

Understanding how valence electrons function is essential to predicting molecular structure and reactivity.

VSEPR Theory

The Valence Shell Electron Pair Repulsion (VSEPR) Theory is used to predict the shape of individual molecules based on the extent of electron-pair electrostatic repulsion. According to VSEPR theory, electron pairs around a central atom are arranged as far apart as possible to minimize repulsion between like charges.Let's look at the molecule \( \mathrm{SnCl}_{2} \):

• \( \mathrm{SnCl}_{2} \) includes a central tin atom that is bonded to two chlorine atoms.
• Besides the bonding pairs of electrons, Sn has one lone pair on it, leading to a bent shape rather than linear.
• This occurs because lone pairs repel more strongly than bonding pairs, adding to the repulsion and bending the molecule.

VSEPR theory is crucial because it helps in understanding molecular geometry, which affects molecular properties and reactions.

Stability of Ionic Compounds

The stability of ionic compounds is influenced by several factors, including the charge on the ions and their ionic potential. Generally, ions with higher charges form more stable ionic compounds due to greater attraction between the positive and negative ions.For example:

• \( \mathrm{Al}^{3+} \), having a greater positive charge than \( \mathrm{Mg}^{2+} \) and \( \mathrm{Na}^{+} \), forms more stable ionic bonds.
• This results in the stability order \( \mathrm{Al}^{3+} > \mathrm{Mg}^{2+} > \mathrm{Na}^{+} \).
• The high charge of \( \mathrm{Al}^{3+} \) means it has greater polarizing power, increasing attraction between ions.

Understanding these principles is valuable for predicting how likely an ionic compound is to form and remain stable.