Question

For each of the questions, four choices have been provided. Select the correct alternative. The lesser covalency of \(\mathrm{FeCl}_{2}\) over \(\mathrm{FeCl}_{3}\) is due to (a) lower polarizing power of \(\mathrm{Fe}^{+2}\) than that of \(\mathrm{Fe}^{+3}\) ion (b) lower polarizing power of \(\mathrm{Fe}^{+3}\) than that of \(\mathrm{Fe}^{+2}\) (c) higher polarizability of \(\mathrm{Fe}^{+3}\) than \(\mathrm{Fe}^{+2}\) (d) higher polarizability of \(\mathrm{Fe}^{+2}\) than \(\mathrm{Fe}^{+3}\)

Short answer

Answer: FeCl₂ has a lesser covalency than FeCl₃ due to the lower polarizing power of Fe²⁺ ion compared to that of the Fe³⁺ ion.

Step-by-step solution

Understand the concepts of polarizing power and polarizability

Polarizing power is the ability of a cation to distort the electron cloud of an anion. A cation with a higher charge density will have a greater polarizing power, which can result in a greater degree of covalency in its bond with an anion. Polarizability refers to the degree to which the electron cloud surrounding an anion can be distorted or polarized by a cation. Anions with larger atomic size and greater electron cloud shielding tend to be more polarizable.

Analyze the given alternatives

We will now analyze each of the given alternatives in relation to the concepts of polarizing power and polarizability: (a) lower polarizing power of Fe²⁺ than that of Fe³⁺ ion (b) lower polarizing power of Fe³⁺ than that of Fe²⁺ (c) higher polarizability of Fe³⁺ than Fe²⁺ (d) higher polarizability of Fe²⁺ than Fe³⁺

Determine the correct alternative

In this case, we are concerned with the polarizing power of Fe²⁺ and Fe³⁺ ions. Since Fe³⁺ has a higher charge density compared to Fe²⁺, it should have higher polarizing power. Greater polarizing power can lead to increased covalency. Therefore, the lesser covalency of FeCl₂ compared to FeCl₃ can be attributed to the lower polarizing power of the Fe²⁺ ion. So, the correct alternative is: (a) lower polarizing power of Fe²⁺ than that of Fe³⁺ ion

Key concepts

Understanding Polarizing Power

Polarizing power is a fundamental concept that plays an integral role in understanding chemical bonds, especially in ionic compounds. It is a measure of how strongly an ion can distort the electron cloud of another. In simple terms, cations, which are positively charged ions, have the ability to distort the electron clouds of nearby anions, negatively charged ions. This distortion can lead to a shift in electron density and the formation of bonds with partial covalent character, even in compounds that are principally ionic.

Factors affecting polarizing power include the charge and size of the cation; a higher charge and smaller size result in greater polarizing power because the charge density is much higher. This aspect of chemical bonding is crucial because it directly influences the covalency of a bond—the degree to which electrons are shared between atoms.

Relevance in Ionic Compounds

In ionic compounds, when cations have considerable polarizing power, they create a more pronounced distortion in the electron clouds of anions. This results in increased overlap of electron orbitals and an enhancement in the sharing of electrons—upticking the covalent bond character.

Exercise Connection

Applying this to the given exercise, an iron ion with a +3 charge (Fe³⁺) will inherently have greater polarizing power than its +2 (Fe²⁺) counterpart due to its higher charge density. As a direct consequence, FeCl₃ would exhibit a higher degree of covalency compared to FeCl₂, earning option (a) as the accurate answer because it acknowledges the lower polarizing power of Fe²⁺.

Examining Polarizability

The concept of polarizability is essential to grasp the nuanced behaviors in chemical interactions. It describes the extent to which an electron cloud around an anion can be distorted. Highly polarizable ions are those which easily have their electron clouds shifted by the electric field of nearby ions or molecules. Factors that boost polarizability include having more electrons (larger anions), having a larger atomic or ionic size, and possessing electrons far from the nucleus which are less tightly held and more easily distorted.

The concept of polarizability enhances our understanding of how molecules interact. In the presence of a highly polarizable ion, we can expect greater bond strength and a higher likelihood of dipole interactions, which are vital for the properties and reactivity of molecules.

Implications in Molecular Behavior

Polarizability has direct implications for the physical properties of substances, such as melting and boiling points, solubility, and even color. A notable example is how polarizability affects the boiling and melting points of halogens; the larger the halogen atom (and hence the greater its polarizability), the higher its boiling and melting points are.

Relation to the Provided Exercise

In the context of the given problem, the idea that Fe²⁺ is more easily polarizable than Fe³⁺ is incorrect. Smaller ions or those with fewer electrons—like the Fe³⁺ ion—are typically less polarizable due to a tighter hold on their electrons. Therefore, options (c) and (d) from the exercise can be disregarded when selecting the correct response.

Covalency and Chemical Bonding

Covalency is a central idea in chemical bonding, underscoring the sharing of electron pairs between atoms. When atoms bond covalently, they fill their outer electron shells by sharing electrons, which leads to the formation of a molecule. The degree of covalency indicates how strongly electrons are shared between atoms, and can vary from pure covalent (equal sharing) to polar covalent (unequal sharing due to differences in electronegativity).

Covalent bonding is the glue that holds together many of the molecules essential to life and the compounds that make up the world around us. It is responsible for the formation of water molecules, the structure of diamond, and the DNA helix.

Variations in Covalency

In chemistry, we learn that not all covalent bonds are created equal; some electrons are shared more equally than others. This can be attributed to the differing electronegativities of the atoms involved. For instance, in a molecule of water (H₂O), the oxygen atom has a higher electronegativity than the hydrogen atoms, resulting in a polar covalent bond.

Understanding Through the Exercise

Linking back to the textbook exercise, covalency comes into play when comparing the bonds in FeCl₂ and FeCl₃. The higher polarizing power of the Fe³⁺ ion in FeCl₃ introduces more of a covalent character to the bonding when compared to FeCl₂. Thus, understanding covalency is crucial, as it explains why FeCl₃ bonds have a lesser degree of ionic character and a greater degree of covalency than those in FeCl₂. This exemplifies why option (a) fits as the correct answer provided in the exercise.