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 the valence and penultimate shells partially filled.

Step 1: Analyzing Element Copper (Cu)

The electronic configuration of copper (Cu) is \([Ar] \ 3d^{10} \, 4s^1\). The 4s subshell is the valence shell, and the 3d subshell is the penultimate shell. The valence shell (4s) is partially filled, while the penultimate shell (3d) is fully filled. Thus, copper does not have both shells partially filled.

Step 2: Analyzing Element Zinc (Zn)

The electronic configuration of zinc (Zn) is \([Ar] \ 3d^{10} \, 4s^2\). The valence shell (4s) is fully filled, and the penultimate shell (3d) is also fully filled. Therefore, zinc does not have both shells partially filled.

Step 3: Analyzing Element Chromium (Cr)

The electronic configuration of chromium (Cr) is \([Ar] \ 3d^5 \, 4s^1\). The valence shell (4s) is partially filled, and the penultimate shell (3d) is also partially filled. Chromium has both the valence shell and the penultimate shell partially filled.

Step 4: Analyzing Element Manganese (Mn)

The electronic configuration of manganese (Mn) is \([Ar] \ 3d^5 \, 4s^2\). The valence shell (4s) is fully filled, but the penultimate shell (3d) is partially filled. Therefore, manganese does not have both shells partially filled.

Key Concepts

Transition Metals

Transition metals are a group of elements found in the center of the periodic table, specifically in the d-block. These elements are unique because:

• They have partially filled d orbitals which contribute to their complex chemistry.
• They often form colored compounds, have variable oxidation states, and are great conductors of electricity.
• Being the metals with partially filled d orbitals, they often act as catalysts in industrial processes due to their ability to easily lend and take electrons.

Examples of transition metals include chromium (\(\mathrm{Cr}\)), copper (\(\mathrm{Cu}\)), manganese (\(\mathrm{Mn}\)), and zinc (\(\mathrm{Zn}\)). These elements are characterized by having electrons filling their d orbitals as they move across the period from left to right. They exhibit unique properties related to their electron configurations, allowing them to form a variety of complex materials.

Valence Shell

The valence shell is the outermost electron shell of an atom. It plays a vital role in chemical reactions and bonding because:

• The electrons in this shell are involved in forming bonds with other atoms.
• A partially filled valence shell makes an element chemically active, more likely to participate in reactions.
• The number of electrons in the valence shell determines the reactivity and the types of bonds an element can form.

For transition metals, the valence shell often includes the s and d orbitals. A great example is chromium (\(\mathrm{Cr}\)) with an electronic configuration of \([Ar] \, 3d^5 \, 4s^1\). Here, the 4s orbital is considered the valence shell, being partially filled, influencing chromium's tendency to form various bonds and compounds.

Partially Filled Shells

Partially filled shells in elements, especially in transition metals, are responsible for much of the diversity in behavior and properties that these elements display. This concept is crucial because:

• Partially filled d and f shells allow elements to exhibit a range of oxidation states, thus influencing their chemistry.
• They contribute to magnetic properties, such as ferromagnetism and paramagnetism.
• They enable the formation of complexes, with metal ions acting as central atoms that form coordination bonds with ligands.

For instance, in the case of chromium (\(\mathrm{Cr}\)), both the 3d and 4s shells are partially filled. This dual partial filling means chromium can engage in various oxidation states and chemical behaviors, making it quite versatile in chemical reactions. Similarly, manganese (\(\mathrm{Mn}\)) has a partially filled 3d shell, which is characteristic of many transition metals, but does not have a partially filled valence shell, which limits some reactivity compared to chromium.