Problem 106 - A Complete Resource Book in Chemistry for JEE Main

Question

The electronic configuration of four elements are (i) \([\mathrm{Xe}] 6 \mathrm{~s}^{1}\) (ii) \([\mathrm{Xe}] 4 \mathrm{f}^{14} 5 \mathrm{~d}^{1} 6 \mathrm{~s}^{2}\) (iii) \([\mathrm{Ar}] 4 \mathrm{~s}^{2} 4 \mathrm{p}^{5}\) (iv) \([\mathrm{Ar}] 3 \mathrm{~d}^{7} 4 \mathrm{~s}^{2}\) Which one of the following statements about these elements is not correct? (a) (i) is a strong reducing agent (b) (ii) is a d block element (c) (iii) has high electron affinity (d) (iv) shows variable oxidation state

Step-by-Step Solution

Answer

Option (b) is not correct; (ii) has more f-electrons, resembling f-block elements.

Step 1: Analyzing the Configuration for (i)

The electronic configuration of (i) is \([\mathrm{Xe}] 6 \mathrm{~s}^{1}\), which belongs to Group 1 elements (alkali metals). Elements in this group are known to be strong reducing agents due to their single electron in the outermost shell, which they tend to lose easily.

Step 2: Identifying the Block for (ii)

The electronic configuration of (ii) is \([\mathrm{Xe}] 4 \mathrm{f}^{14} 5 \mathrm{~d}^{1} 6 \mathrm{~s}^{2}\). This configuration ends in the d-block (5d), indicating it belongs to the d block elements.

Step 3: Checking Electron Affinity for (iii)

Element (iii), with configuration \([\mathrm{Ar}] 4 \mathrm{~s}^{2} 4 \mathrm{p}^{5}\), is in Group 17, the halogens. Halogens typically have high electron affinities as they are one electron short of a complete valence shell.

Step 4: Determining Oxidation States for (iv)

The electronic configuration of (iv) \([\mathrm{Ar}] 3 \mathrm{~d}^{7} 4 \mathrm{~s}^{2}\) corresponds to a transition metal in the d-block, specifically in Group 9 (cobalt group). Transition metals are known for exhibiting variable oxidation states.

Key Concepts

Reducing Agents

Reducing agents are substances that lose electrons easily, allowing them to reduce other substances by transferring electrons to them. Think of them as electron donors. They are incredibly important in various chemical reactions.

• Characteristics: Typically, metals are good reducing agents because they have a tendency to lose electrons.
• Group 1 alkali metals, such as those with a configuration like \([\mathrm{Xe}] 6 \mathrm{~s}^{1}\), are strong reducing agents. This is because they have only one electron in their outermost shell, and they prefer to lose this electron to achieve a more stable electron configuration.
• Significance: Reducing agents are crucial in processes like corrosion, energy production, and synthesis reactions where electron transfer is essential.

In summary, reducing agents are vital players in chemistry, working towards achieving stability through electron transfer.

Electron Affinity

Electron affinity measures the tendency of an atom to accept an electron. It is the energy released when an electron is added to a neutral atom in the gas phase, forming a negative ion.

• High Electron Affinity: Elements like the halogens (Group 17), characterized by configurations such as \([\mathrm{Ar}] 4 \mathrm{~s}^{2} 4 \mathrm{~p}^{5}\), have high electron affinities. This is because they are just one electron short of a full p subshell, making them eager to gain that electron.
• Trends: Electron affinity generally increases across a period (left to right on the periodic table) and decreases down a group. This correlates with how close the added electron comes to the nucleus.
• Applications: Electron affinity is important in predicting the reactivity of elements and helps in understanding bond formation and energy changes during reactions.

Overall, understanding electron affinity aids in explaining the reactivity and chemical behavior of elements.

D Block Elements

D block elements, also known as transition metals, occupy the central block of the periodic table. They include elements in groups 3 to 12 and are characterized by a partially filled d orbital.

• Electronic Configuration: Many d block elements have a general configuration that involves the "d" subshell, such as \([\mathrm{Xe}] 4 \mathrm{f}^{14} 5 \mathrm{~d}^{1} 6 \mathrm{~s}^{2}\).
• Characteristics: These elements are known for their ability to form colorful compounds, exhibit magnetism, and have high melting and boiling points.
• Catalytic Ability: Transition metals are often used as catalysts in chemical reactions due to their ability to lend and take electrons from reaction intermediates.

D block elements are pivotal in industrial applications and biological systems due to their unique properties and versatility.

Oxidation States

Oxidation states indicate the degree of oxidation (loss of electrons) of an atom in a chemical compound. It's a useful concept for understanding redox (reduction-oxidation) reactions.

• Variety: Transition metals, which include elements with configurations like \([\mathrm{Ar}] 3 \mathrm{~d}^{7} 4 \mathrm{~s}^{2}\), are renowned for having multiple oxidation states. This is due to the involvement of both their "s" and "d" electrons in bonding.
• Significance: The ability to exist in multiple oxidation states allows these elements to form a wide variety of compounds with different properties and colors. This is especially notable in processes such as catalysis and electron transfer reactions.
• Examples: Elements like iron, which can exist in the +2 or +3 oxidation state, are examples where oxidation states are critical in their chemical behavior and applications.

Understanding oxidation states helps in the analysis of chemical reactions and the properties of compounds formed by elements.