Question

Which of the following statements is wrong? (1) The rule that limits the maximum number of electrons in an orbital to two is Paulis exclusion principle. (2) IIund's rule states that in a set of degenerate orbitals the electrons distribute with parallel spins. (3) The order of filling of electrons in the orbitals of an atom will be \(5 \mathrm{~s}, 4 \mathrm{p}, 3 \mathrm{~d}, 4 \mathrm{~d}, 4 \mathrm{~s}\). (4) The number of unpaired electrons in the electronic configuration \(1 \mathrm{~s}^{2} 2 \mathrm{~s}^{2} 2 \mathrm{p}^{4}\) is 2 .

Short answer

Statement (3) is wrong.

Step-by-step solution

Examine Statement 1

The statement 'The rule that limits the maximum number of electrons in an orbital to two is Pauli's exclusion principle' describes Pauli’s exclusion principle correctly. Each orbital can hold a maximum of two electrons with opposite spins. Therefore, statement (1) is true.

Examine Statement 2

The statement 'Hund's rule states that in a set of degenerate orbitals the electrons distribute with parallel spins' is a correct explanation of Hund’s rule. According to this rule, electrons fill degenerate orbitals singly first, with parallel spins, before pairing up. Statement (2) is true.

Examine Statement 3

Evaluate the order of filling electrons: The correct order of orbital filling based on the Aufbau principle should be based on increasing energies. The order should be 4s, 3d, 4p, 5s, 4d, and so on. The given order '5s, 4p, 3d, 4d, 4s' is incorrect. Therefore, statement (3) is wrong.

Examine Statement 4

The electronic configuration given is '1s² 2s² 2p⁴'. According to this configuration, the 2p orbital has 4 electrons, which means there are 2 unpaired electrons. Therefore, statement (4) is true.

Key concepts

Hund's Rule

In atomic physics, Hund's Rule is crucial for understanding how electrons populate orbitals. According to Hund's Rule, every orbital in a subshell becomes singly occupied before any orbital is doubly occupied.
Electrons placed in singly occupied orbitals must have parallel spins.

• This minimizes electron repulsion because it keeps the electrons as far apart as possible.
• For instance, in the case of the 2p orbital, if it has three electrons, each will occupy a different orbital with parallel spins before any two electrons pair up.

Understanding Hund's Rule can help predict the structure and properties of molecules, as how electrons are arranged affects the chemical behavior of atoms extensively. So, remember: half-fill before pairing, and maintain parallel spins for minimized repulsion.

Aufbau Principle

The Aufbau Principle is fundamental for determining the order in which electrons fill orbitals in an atom. 'Aufbau' is German for 'building up,' which perfectly describes how this principle works.
This principle states that electrons fill orbitals starting from the lowest energy level before advancing to higher levels.
The correct order of filling is often remembered by using the diagonal rule or by following the sequence provided by the periodic table:

• First, fill the 1s orbital, then 2s, 2p, 3s, 3p, 4s, and so on.
• It ensures that the atom remains in its lowest energy state or ground state.

As an example:
The electronic configuration of carbon (6 electrons) can be written as 1s² 2s² 2p². According to Aufbau's Principle, we fill the 1s orbital first, then 2s, and finally start filling the 2p orbitals. This principle helps in predicting the electronic structure of atoms and is significant in understanding chemical reactivity and bonding.

Electronic Configuration

Electronic Configuration refers to the distribution of electrons in an atom's orbitals. This distribution follows a set of rules:

• The Pauli Exclusion Principle states that no two electrons in an atom can have the same four quantum numbers, essentially limiting each orbital to a maximum of two electrons with opposite spins.
• The Aufbau Principle guides the order in which orbitals are filled based on increasing energy levels.
• Hund's Rule ensures that electrons will populate empty orbitals singly with parallel spins before pairing up.

A correct electronic configuration provides insight into the chemical behavior of the element.
For example, the configuration for oxygen (8 electrons) is 1s² 2s² 2p⁴. This tells chemists that oxygen has two unpaired electrons and a propensity to form bonds by pairing these electrons with electrons from other atoms.
Understanding electronic configurations is essential for studying how atoms interact and form molecules, helping anticipate bonding patterns and the resulting properties of a substance.