Problem 1 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

In the sixth period, the orbitals that are filled are: [Main Sep. \(\mathbf{0 5}, \mathbf{2 0 2 0}\) (I)] (a) \(6 s, 4 f, 5 d, 6 p\) (b) \(6 s, 5 d, 5 f, 6 p\) (c) \(6 s, 5 f, 6 d, 6 p\) (d) \(6 s, 6 p, 6 d, 6 f\)

Step-by-Step Solution

Answer

Option (a) is correct: 6s, 4f, 5d, 6p are filled in the sixth period.

Step 1: Identify the Period and Principal Quantum Number

We are looking at the sixth period of the periodic table. The principal quantum number ( ) corresponding to this period is 6. This means that energy levels of orbitals beginning with '6' will be filled in this period.

Step 2: Determine the Order of Filling Using Aufbau Principle

Application of the Aufbau principle helps in determining the order of filling electron orbitals. In the sixth period, electrons fill the orbitals in order: \(6s\), \(4f\), \(5d\), and finally \(6p\).

Step 3: Check Each Option Against the Filling Order

Review each option to see if it matches the filling order determined in the previous step:- (a) \(6s, 4f, 5d, 6p\)- (b) \(6s, 5d, 5f, 6p\)- (c) \(6s, 5f, 6d, 6p\)- (d) \(6s, 6p, 6d, 6f\)Option (a) correctly follows the order: \(6s\), \(4f\), \(5d\), \(6p\).

Key Concepts

Electron Configuration

The term 'electron configuration' describes the arrangement of electrons within an atom's orbitals. Electrons orbit the nucleus in specific energy levels, or shells, which are divided into different subshells labeled as s, p, d, and f.
Each subshell can accommodate a specific number of electrons as follows:

• The s subshell can hold up to 2 electrons
• The p subshell can hold up to 6 electrons
• The d subshell can hold up to 10 electrons
• The f subshell can hold up to 14 electrons

Electron configuration follows a set of rules that help in predicting the distribution of electrons in atoms. This distribution plays a vital role in determining the chemical properties of an element.
Understanding how electrons are configured allows scientists to understand and predict chemical behavior and bonding characteristics of the elements.

Quantum Numbers

Quantum numbers provide an important framework for understanding the configuration of electrons. They define the position of an electron in an atom and provide a unique address for each electron, much like a postal code system.
There are four quantum numbers:

• The Principal Quantum Number ( ) indicates the main energy level and can be any positive integer (1, 2, 3, ...). In the sixth period, is 6.
• The Azimuthal Quantum Number (l) defines the subshell of the electron and can be 0, 1, 2, 3,... up to ( -1). Values correspond to s, p, d, and f orbitals.
• The Magnetic Quantum Number (m) shows the specific orbital within a subshell, ranging from -l to +l.
• The Spin Quantum Number (s) indicates the spin of the electron, either +1/2 or -1/2.

By understanding these numbers, you can pinpoint where each electron resides in the atom's electron cloud, ensuring a full grasp of the electron's role in atomic structure.

Aufbau Principle

The Aufbau Principle is a key concept for determining electron configuration. It states that electrons occupy the lowest energy orbitals first before moving to higher ones.
This principle is represented visually using an aufbau diagram, illustrating the sequence in which electrons populate atomic orbitals. For the sixth period, this means:

• Electrons fill the 6s orbital first
• Followed by the 4f orbital
• Then the 5d orbital
• Finally, the 6p orbital

This step-by-step filling order is essential for correctly describing the structure of the electron cloud in atoms.
By applying this principle, learners can easily follow the logical sequence of electron filling and accurately write the electron configuration of elements within the periodic table.