Question

"Pairing of electrons in orbitals starts only when the available degenerate orbitals are singly filled" is stated by

• A. Hund's Rule
• B. Pauli's Principle
• C. Aufbau Principle
• D. Bohr's theory

Answer 1

The Correct Option is A

To determine which principle or rule states that "pairing of electrons in orbitals starts only when the available degenerate orbitals are singly filled," we need to analyze the given options and their respective principles.

1. Understanding the Principles:

• Hund's Rule: This rule states that electrons will occupy degenerate orbitals (orbitals with the same energy) singly before pairing up. Each orbital must have one electron with parallel spin before any orbital is occupied by a second electron with opposite spin.
• Pauli's Exclusion Principle: This principle states that no two electrons in an atom can have the same set of four quantum numbers. It restricts the number of electrons that can occupy a single orbital to two, with opposite spins.
• Aufbau Principle: This principle describes the order in which atomic orbitals are filled as protons are added to form the neutral atoms of the elements. Electrons fill the lowest-energy orbitals first.
• Bohr's Theory: This theory, proposed by Niels Bohr, explains the structure of the atom and the behavior of electrons in terms of quantized energy levels. It does not directly address the filling of orbitals or electron pairing.

2. Identifying the Correct Principle:
The statement "pairing of electrons in orbitals starts only when the available degenerate orbitals are singly filled" directly corresponds to Hund's Rule. This rule ensures that electrons maximize the total spin of the system by occupying different orbitals before pairing.

3. Conclusion:
The principle that states this rule is Hund's Rule.

Final Answer: $ {\text{Hund's Rule}} $