Book cover for Objective Chemistry for Engineering and Medical Entrance Examinations

Objective Chemistry for Engineering and Medical Entrance Examinations

K Rama Rao

ISBN #9789332541771

1st Edition

2,463 Questions

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12,716 Students Helped

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

The chapter on the Boron Family of Group-III (13) elements highlights that despite a common outer electronic configuration (ns2 np1), differences in penultimate electron counts result in significant variations in reactivity, physical properties, and abundance among boron, aluminium, gallium, indium, and thallium. In particular, thallium's ability to exist in both +1 and +3 oxidation states underlines its unique chemical behavior, leading to various specialized applications. Recognizing these subtle differences is crucial for understanding their roles in industrial and technological contexts.

Learning Objectives

1

Describe the outer electronic configuration (ns2 np1) common to Group-III (13) elements.

2

Explain how differences in penultimate electron counts lead to varied reactivity, physical properties, and natural abundance among boron, aluminium, gallium, indium, and thallium.

3

Analyze the significance of thallium's ability to exhibit both +1 and +3 oxidation states and its impact on chemical behavior.

4

Evaluate the diverse industrial and technological applications of the boron family elements.

Key Concepts

CONCEPT

DEFINITION

Boron Family

A group of elements in Group-III (13) of the periodic table that includes boron, aluminium, gallium, indium, and thallium, sharing a common outer electronic configuration of ns2 np1.

Outer Electronic Configuration (ns2 np1)

The arrangement of electrons in the outermost shell of the element, determining many of its chemical properties.

Penultimate Electron Count

The number of electrons in the second-to-last electron shell, which influences the reactivity and physical properties of an element.

Oxidation State

The degree of oxidation of an atom in a chemical compound, representing the number of electrons lost, gained, or shared during chemical reactions, with thallium capable of adopting +1 and +3 states.

Example Problems

Example 1

Which of the following statements is falsc? (1) Thallium shows different oxidation states because of inert pair effect. (2) Stable compounds in $+1$ oxidation state are formed by thallium. (3) Inert pair is a pair of outmost electrons which act as inert. (4) Among III A group elements, aluminium is present in cations only.

Example 2

Boron diffcrs from the other members of III $\Lambda$ group because it (1) has much lesser radius. (2) is non-metal. (3) is covalent in its compounds. (4) has maximum covalency of 6 .

Example 3

Which of the following statements is false? (1) The most abundant metal in the Earth crust is aluminium. (2) Boron never form $\mathrm{B}^{3-}$ ion. (3) Among III A elements, boron has the lowest melting point. (4) Owing to small size and more charge on $\mathrm{M}^{3-}$ ion of III A group elements, their aqueous solutions are acidic, and their acidic nature increases from $\mathrm{A} 1^{3-}$ to $\mathrm{Tl}^{3+}$

Example 4

$\Lambda$ n clement $R$ is in III $\Lambda$ group. Which is true with respect to $\mathrm{R} ?$ (1) It is a gas at room temperature. (2) It has an oxidation state of $+4$. (3) It forms an oxide of the type $\mathrm{R}_{2} \mathrm{O}_{3}$. (4) It forms a halide of the type $\mathrm{RX}_{2}$.

Example 5

Boron differs from other members of III A because of its (1) small size, high ionization potential and absence of $d$ -orbitals. (2) large size, low ionization potential and presence of $d$ -orbitals. (3) small size, low ionization potential and absence of $d$ -orbitals. (4) large size, high ionization potential and absence of $d$ -orbitals.
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Step-by-Step Explanations

QUESTION

How does thallium exhibit both +1 and +3 oxidation states, and what factors contribute to this behavior?

STEP-BY-STEP ANSWER:

Step 1: Identify thallium's outer electronic configuration and note its ns2 np1 configuration.
Step 2: Consider the energy difference between removing one electron versus three electrons from thallium, paying special attention to the stability provided by electron removal from the penultimate shell.
Step 3: Understand that the ability of thallium to lose only one electron to form the +1 state is due to lower energy requirements compared to removing additional electrons required for the +3 state.
Step 4: Recognize that relativistic effects and electron shielding also play a role in stabilizing the +1 state more in some chemical environments.
Final Answer: Thallium's dual oxidation states result from its nuanced electronic structure where differences in energy needed to remove electrons, combined with relativistic effects and shielding, enable the stability of both +1 and +3 states.

Oxidation State Variation in Thallium

QUESTION

Why do differences in the penultimate electron counts among boron family elements affect their physical and chemical properties?

STEP-BY-STEP ANSWER:

Step 1: Recognize that while all Group-III elements share a common outer electronic configuration (ns2 np1), the number of electrons in the inner (penultimate) shell varies among them.
Step 2: Explain that variations in penultimate electrons influence electron-electron interactions, chemical reactivity, and atomic size.
Step 3: Connect these differences to observable properties such as melting point, density, conductivity, and reactivity, which vary among the elements in the boron family.
Final Answer: The differences in the penultimate electron counts lead to variations in electron shielding and bonding characteristics, thereby affecting the reactivity, physical properties, and natural abundance of the elements within the boron family.

Impact of Penultimate Electron Count

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Common Mistakes

  • Assuming that all Group-III elements have identical chemical and physical properties due only to their ns2 np1 configuration.
  • Overlooking the impact of penultimate electron counts on the reactivity and stability of each element.
  • Misunderstanding the significance of thallium's dual oxidation states, often attributing its unusual behavior to experimental anomalies rather than its electronic structure.
  • Neglecting the real-world applications and industrial importance of these elements by focusing solely on theoretical electronic configurations.