Question

The incorrect statement regarding Aluminium \& Thallium: (1) Tl is more electropositive than Al. (2) \(\mathrm{Al}\) is more electropositive than Thallium. (3) \(\mathrm{Tl}^{+3}\) is more stable than \(\mathrm{Al}^{+}\). (4) \(\mathrm{Tl}^{+3}\) is a powerful reducing agent. (a) \(1,2,3\) (b) \(1,3,4\) (c) \(2,3,4\) (d) 1,4

Short answer

The answer is (b) 1,3,4.

Step-by-step solution

Understand Electropositivity

Electropositivity refers to the tendency of an element to lose electrons and form positive ions. A more electropositive element loses electrons more easily.

Compare Electropositivity in Aluminium (Al) and Thallium (Tl)

Aluminium (Al) is located above Thallium (Tl) in Group 13 of the periodic table. In general, electropositivity decreases down a group. Thus, Aluminium is more electropositive than Thallium.

Analyze Statement 1

Statement (1) "Tl is more electropositive than Al" contradicts the known trend that Aluminium is more electropositive. Therefore, this statement is incorrect.

Analyze Statement 2

Statement (2) "Al is more electropositive than Thallium" is consistent with known periodic trends, making it correct.

Assess Stability of Ions

Examine stability across ions. (3) "Tl^{+3} is more stable than Al^{+}": Here, since Tl generally forms +1 oxidation rather than +3 due to inert pair effect, this statement is incorrect.

Evaluate Tl3+ as a Reducing Agent

Statement (4) "Tl^{+3} is a powerful reducing agent" is correct; Tl^3+ can easily gain electrons to become Tl^{+} due to its tendency to revert to a more stable state.

Review Listed Options

Review which statements were marked incorrect in analyzing (1), (3), and (4). Correspond this with given options to find match with incorrect statements.

Identify the Correct Answer

Based on the analysis, Statements (1) and (3) are incorrect, thus the option containing "1,3,4" should be reviewed. Option (b) "1,3,4" is the correct answer.

Key concepts

Aluminium and Thallium comparison

Aluminium (Al) and Thallium (Tl) are both members of Group 13 in the periodic table, making them part of the same chemical family. As we examine these elements, it's important to focus on their similarities and differences, especially regarding electropositivity.

• Location in the Periodic Table: Aluminium sits above Thallium. This relative positioning affects their chemical properties.
• Electropositivity: Electropositivity is the tendency of an atom to lose electrons and form positive ions. Generally, moving down a group in the periodic table results in a decrease in electropositivity. This means Aluminium is more electropositive than Thallium, contradicting any claims that Thallium might be more electropositive.
• Physical State: Both elements are metals. Aluminium is lightweight and has a low density, while Thallium is heavier and denser, reflecting their differing positions in the group.

It is crucial for students to accurately understand the distinctions and commonalities between these two elements to predict and rationalize their behavior in chemical reactions.

Periodic trends

Periodic trends are recurring patterns that help in predicting how an element will behave based on its position in the periodic table. Understanding these trends is key to mastering chemistry.

• Electropositivity Trend: As one moves down a group, atoms have more electron shells, making their valence electrons further from the nucleus. This causes a decrease in electropositivity down the group, contributing to the fact that Aluminium is more electropositive than Thallium.
• Inert Pair Effect: This is particularly relevant for heavier elements like Thallium. It explains why Tl tends to favor a +1 oxidation state over +3, as electrons in the higher s orbital are more "fixed" and less likely to participate in bonding.
• Atomic Radius: The size of atoms increases down a group due to the addition of electron shells. This affects where electrons lie and is a crucial factor in electropositivity, reactivity, and other properties.

Grasping these trends allows students to make informed predictions about element behavior, both individually and in compounds.

Ion stability

Ion stability is a critical concept in chemistry, as it influences how ions form, react, and stabilize in various chemical environments.

• Stability in Group 13: Aluminium typically forms the +3 oxidation state, while Thallium often forms +1. This is due to the inert pair effect, which makes the +1 state more stable for Thallium.
• Inconsistencies: Statement  of the exercise asserts  that Tl^{+3} is more stable than Al^{+} which is incorrect. Thallium prefers the +1 state due to reduced energy from bonding in the stable configuration.
• Thermodynamics: Ion stability can be attributed to bond energies and lattice energies in compounds. More stable ions form more stable compounds with stronger bonds.

Grasping the idea of ion stability helps in understanding why certain reactions occur and the compounds they produce.

Electropositivity in Group 13

In Group 13, electropositivity plays an integral role in defining the chemistry of the elements.

• Trends and Effects: As mentioned earlier, electropositivity decreases down the group. This trend explains why Aluminium, being higher on the table, is more electropositive than Thallium.
• Link to Metal Reactivity: Higher electropositivity indicates a greater tendency to lose electrons and participate in typical metallic reactions like oxidation.
• Role in Reactions: A more electropositive element can serve as a good reducing agent, donating electrons to other elements. However, Thallium's tendency to form the +1 oxidation state due to the inert pair effect tempers its reactivity.

Having a firm understanding of electropositivity within this group provides necessary insights into predicting reaction pathways and determining suitable applications for these group elements.