Question

(a) Which of the following compounds has the greatest ionic character: \(\mathrm{PCl}_{5}, \mathrm{SiCl}_{4}, \mathrm{CCl}_{4}, \mathrm{BCl}_{3} ?(\mathrm{~b})\) Which of the following ions has the smallest ionic radius: \(\mathrm{F}^{-}, \mathrm{C}^{4-}, \mathrm{N}^{3-}, \mathrm{O}^{2-} ?(\mathrm{c})\) Which of the following atoms has the highest ionization energy: \(\mathrm{F}, \mathrm{Cl}, \mathrm{Br}, \mathrm{I} ?\) (d) Which of the following oxides is most acidic: \(\mathrm{H}_{2} \mathrm{O}, \mathrm{SiO}_{2}, \mathrm{CO}_{2} ?\)

Short answer

(a) SiCl"]\(\{}4\)\(\)\, (b) F^-\, (c) F\, (d) CO_2\)

Step-by-step solution

Identify Ionic Character in Compounds

To determine which compound has the greatest ionic character, consider the electronegativity difference between the central atom and chlorine (Cl). A larger difference indicates greater ionic character. The electronegativities are: P (2.1), Si (1.9), C (2.5), B (2.0) and Cl (3.0). Calculate the difference for each:- For \mathrm{PCl}_{5}, it is \(3.0 - 2.1 = 0.9\)- For \mathrm{SiCl}_{4}, it is \(3.0 - 1.9 = 1.1\)- For \mathrm{CCl}_{4}, it is \(3.0 - 2.5 = 0.5\)- For \mathrm{BCl}_{3}, it is \(3.0 - 2.0 = 1.0\).The greatest electronegativity difference is for \( ext{SiCl}_{4}\), so it has the greatest ionic character.

Determine the Smallest Ionic Radius for Ions

The ionic radius generally decreases with a decrease in the negative charge for isoelectronic species since electrons are less repelled by less negative charges. The ions to compare are \(\text{F}^{-}, \text{C}^{4-}, \text{N}^{3-}, \text{O}^{2-}\). All these ions are isoelectronic with neon (10 electrons), but as the charge becomes less negative, the radius decreases. Hence, \(\text{F}^{-}\) has the smallest ionic radius as it has the smallest charge.

Identify Atom with Highest Ionization Energy

Ionization energy generally decreases down a group on the periodic table as atomic size increases. Comparing \(\text{F}, \text{Cl}, \text{Br}, \text{I}\), fluorine is at the top of the group, thus has the highest ionization energy due to its small atomic size and high effective nuclear charge.

Determine Most Acidic Oxide

Acidity of oxides increases with the presence of non-metallic character, often related to their position in the periodic table. Observing \(\text{H}_2\text{O}, \text{SiO}_2, \text{CO}_2\), carbon dioxide \(\text{CO}_2\) is a non-metal oxide and forms carbonic acid \(\text{H}_2\text{CO}_3\) in water, making it the most acidic among the options.

Key concepts

Ionic Character

Ionic character in a compound refers to the extent to which electrons are transferred between atoms, creating ions. This is often gauged by the difference in electronegativity between the atoms involved.
- Electronegativity is a measure of an atom's ability to attract bonding electrons.- A greater difference in electronegativity between two atoms indicates a higher ionic character since one atom will more strongly attract the electrons.
In the problem, comparisons were made between compounds like \(\mathrm{PCl}_{5}, \mathrm{SiCl}_{4}, \mathrm{CCl}_{4}, \mathrm{BCl}_{3}\). Each compound involves chlorine (Cl), which has an electronegativity of 3.0. Evaluating each central atom: P (2.1), Si (1.9), C (2.5), and B (2.0), Si has the largest electronegativity difference from Cl, making \(\mathrm{SiCl}_{4}\) have the greatest ionic character. Remember: comparing electronegativity differences allows us to predict ionic character accurately.

Ionic Radius

The ionic radius is the effective distance from the nucleus of the ion to the edge of its electron cloud. It becomes particularly important when comparing ions that have the same number of electrons, known as isoelectronic ions.
Consider the ions given: \(\mathrm{F}^{-}, \mathrm{C}^{4-}, \mathrm{N}^{3-}, \mathrm{O}^{2-}\). - These ions all have neon's electron configuration but vary in their nuclear charge. - The more negative an ion, the more electrons it has compared to protons, increasing repulsion among electrons and thus, a larger radius.
To determine the smallest ionic radius, observe the negative charge; \(\mathrm{F}^{-}\) with a charge of -1 has the least electron repulsion and thus, the smallest ionic radius amongst the compared ions.

Ionization Energy

Ionization energy is the energy required to remove the outermost electron from a neutral atom in its gaseous state. This property reflects how tightly bound an electron is to an atom.
Several factors impact ionization energy:

• Atomic size: Smaller atoms have higher ionization energies as the outer electrons are closer to the nucleus.
• Nuclear charge: Greater nuclear charge can hold the electrons more tightly, meaning more energy is needed to remove them.
• Electron shielding: Increase in inner electron layers can reduce the effective nuclear charge felt by outer electrons, lowering ionization energy.

When comparing \(\mathrm{F}, \mathrm{Cl}, \mathrm{Br}, \mathrm{I}\), notice their positions in the periodic table. - Fluorine, at the top of the group, undergoes the least electron shielding and, being the smallest, possesses the highest ionization energy. Thus, fluorine emerges as the element with the highest ionization energy.

Acidic Oxides

Acidic oxides are formed when nonmetals react with oxygen. They can release acids upon their interaction with water, which is a key characteristic of these oxides.
Consider the options: \(\mathrm{H}_{2} \mathrm{O}, \mathrm{SiO}_{2}, \mathrm{CO}_{2}\).- Water \(\mathrm{H}_{2} \mathrm{O}\) is neutral, not displaying prominent acidic properties.- \(\mathrm{SiO}_{2}\) is a weakly acidic oxide with limited reaction with water.
- \(\mathrm{CO}_{2}\) is a classic acidic oxide; it reacts with water to form carbonic acid, \(\mathrm{H}_2\mathrm{CO}_3\), thus showing strong non-metallic, acidic properties. Non-metal oxide acidity increases across a period and decreases down the group, linking deeply to their position in the periodic table. Hence, \(\mathrm{CO}_{2}\) is the most acidic among the choices due to its vigorous reaction with water.