Problem 104 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following metals have both valence shell and penultimate shell partially filled? (a) \(\mathrm{Cu}\) (b) \(\mathrm{Zn}\) (c) \(\mathrm{Cr}\) (d) \(\mathrm{Mn}\)

Step-by-Step Solution

Answer

Chromium (Cr) has both valence and penultimate shells partially filled.

Step 1: Understand the Periodic Table Configuration

Valence shell refers to the outermost shell of electrons in an atom. The penultimate shell is the shell just before the valence shell. A partially filled shell is one that does not have the maximum number of electrons it can hold.

Step 2: Write the Electron Configuration of Each Metal

To determine whether both the valence shell and penultimate shell are partially filled, we need to look at the electron configuration of each element:- Cu (Copper): [Ar] 3d\(^{10}\) 4s\(^{1}\)- Zn (Zinc): [Ar] 3d\(^{10}\) 4s\(^{2}\)- Cr (Chromium): [Ar] 3d\(^{5}\) 4s\(^{1}\)- Mn (Manganese): [Ar] 3d\(^{5}\) 4s\(^{2}\)

Step 3: Analyze Each Electron Configuration

- Cu: The valence shell (4s) is partially filled, but the penultimate shell (3d) is completely filled. - Zn: Both the valence (4s) and penultimate (3d) shells are completely filled. - Cr: The valence shell (4s) is partially filled and the penultimate shell (3d) is also partially filled. - Mn: The valence shell (4s) is completely filled, but the penultimate shell (3d) is partially filled.

Step 4: Determine the Correct Metal

Based on the electron configurations, Chromium (Cr) is the metal where both the valence shell (4s) and the penultimate shell (3d) are partially filled. This meets the criteria of the exercise.

Key Concepts

Valence Shell

The valence shell is the outermost electron shell of an atom. It plays a crucial role in determining a chemical element's behavior. This shell is significant because the electrons found in it are often the ones involved in chemical bonding and reactions.

Valence electrons can determine if an atom will gain, lose, or share electrons during a chemical reaction. For instance, in the exercise provided, when analyzing Copper (Cu), the valence shell is 4s. It contains only one electron, indicating it is partially filled, which influences how copper behaves chemically.

• Outermost electron shell of an atom
• Involves in bonding and chemical reactions
• Influences reactivity of the element

Understanding the valence shell is fundamental to predicting how each element will interact with others, making it a key concept in chemistry.

Penultimate Shell

The penultimate shell of an atom is the electron shell that lies just before the valence shell. It is also known as the second-to-last shell. Understanding its configuration helps to explain certain chemical properties, especially in transition metals.

For example, in the case of Chromium (Cr), the penultimate shell is the 3d subshell. It is partially filled with five electrons. This partial filling is important because it leads to unique properties such as higher magnetic behavior.

• Located just before the valence shell
• Includes transition metals' characteristic d-orbitals
• Affects chemical and physical properties

This shell is vital in chemistry because it contributes to the bonding and characteristics of transition metals.

Partially Filled Shells

A partially filled electron shell plays a major role in the reactivity and properties of an atom. A shell is considered partially filled if it has spaces available for more electrons, according to the maximum it can hold. This state leads to interesting characteristics such as enhanced affinity to bond and unique magnetic properties.

In the exercise, both the valence and penultimate shells are analyzed for being partially filled. Chromium (Cr) is highlighted because its 3d and 4s are not fully filled, which is uncommon and of profound chemical importance.

• Shells with space for more electrons
• Leads to reactivity and special magnetic properties
• Common in transition metals, causing unique behaviors

Recognizing partially filled shells helps in understanding complex bonding scenarios within chemical reactions.