Problem 43 - A Complete Resource Book in Chemistry for JEE Main

Question

Why \(\operatorname{Sc}(Z=21)\) is not considered as a transition element? (a) properties of \(\mathrm{Sc}\) are similar to alkali metals (b) \(3 \mathrm{~d}\) orbitals are empty in its stable compound (c) stable oxidation number of \(\mathrm{Sc}\) is \(+2\) (d) atomic volume of \(\mathrm{Sc}\) is very large

Step-by-Step Solution

Answer

(b) 3d orbitals are empty in its stable compound.

Step 1: Understanding Transition Elements

Transition elements are typically defined as elements that have partially filled d orbitals in at least one of their common oxidation states.

Step 2: Configuration of Scandium

The electron configuration of scandium (Sc) is \( [Ar] 3d^1 4s^2 \). In its most stable oxidation state, Sc forms Sc³⁺ by losing three electrons, resulting in an electronic configuration of \( [Ar] \), with empty 3d orbitals.

Step 3: Examining Scandium's Stable Compounds

In its compounds, scandium usually exhibits a +3 oxidation state. This means that in these compounds, the 3d orbitals are empty as all three valence electrons are lost, contradicting the requirement for a transition metal to have partially filled d orbitals.

Step 4: Conclusion to Answer Choice

Since scandium's stable oxidation state has empty 3d orbitals (not partially filled as required for transition elements), the correct answer is that the 3d orbitals are empty in its stable compound.

Key Concepts

d orbitals

Transition elements are defined by the presence of electrons in their d orbitals. These orbitals are a type within the electron structure where electrons can form bonds and reflect various oxidation states. Unlike s and p orbitals, d orbitals have more complex shapes and can hold up to 10 electrons in total. This ability allows transition metals to exhibit multiple oxidation states.

• In transition metals, d orbitals can be partially filled, creating a variety of chemical properties.
• Partially filled d orbitals are crucial during chemical reactions, as they participate in bonding and electron sharing.

Understanding d orbitals is key to comprehending how transition elements behave, especially in forming compounds with distinct colors and magnetic properties. However, scandium lacks this feature in its stable form, which plays a significant role in its classification.

oxidation state

An element’s oxidation state refers to the degree of oxidation, essentially representing the number of electrons an atom loses, gains, or shares during chemical reactions. In transition metals, varying oxidation states are due to the flexible nature of d orbitals.

• Transition metals typically show variable oxidation states, as they can lose different numbers of d electrons.
• The variety in oxidation states allows these elements to form a wide range of compounds.

For scandium (Sc), it primarily exhibits an oxidation state of +3 in its compounds. This +3 state results in the complete removal of electrons from its 3d and 4s orbitals, leading to empty d orbitals—one reason it’s not a transition element by definition.

scandium (Sc)

Scandium (Sc), with an atomic number of 21, is often closely examined in transition metal studies, although it’s technically not a transition metal. Found naturally in rare minerals, scandium is light, soft, and displays characteristics similar to both transition metals and alkaline earth metals.

• Scandium is typically found in its +3 oxidation state.
• Unlike other transition metals, scandium does not have a rich array of oxidation states.

This +3 state results in empty 3d orbitals, setting it apart from the traditional definition of transition metals with partially filled d orbitals. Therefore, despite its position in the periodic table, scandium doesn't satisfy the criteria to be a transition element.

electron configuration

An element's electron configuration describes how electrons are distributed among its atomic orbitals. For scandium (Sc), the electron configuration is typically written as \([Ar] 3d^1 4s^2\) when neutral. This configuration changes when scandium forms ions.

• In its common +3 oxidation state, scandium loses its 3d and both 4s electrons, becoming \( [Ar] \) with no electrons in the 3d orbital.
• This complete loss of electrons in the d orbitals prevents scandium from being classified as a transition metal.

In contrast, true transition metals retain partially filled d orbitals even when forming ions, providing them with unique attributes such as complex ion formation, varied oxidation states, and specific catalytic properties. Scandium's transition to \([Ar]\) in its +3 state fundamentally precludes it from these characteristics.