Problem 27 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The orbital diagram in which the Aufbau principle is violated is: (b) \begin{tabular}{|l|l|l|l|} \cline { 2 - 5 } & \(\uparrow \downarrow\) & \(\uparrow\) & \(\uparrow\) \\ \hline \end{tabular} \begin{tabular}{l|l|l|l|l|} (c) & \(\uparrow \downarrow\) & \(\uparrow\) & \(\uparrow\) & \(\uparrow\) \\ \hline \end{tabular}

Step-by-Step Solution

Answer

Orbital diagram (c) violates the Aufbau principle.

Step 1: Understanding the Aufbau Principle

The Aufbau principle states that electrons fill orbitals starting with the lowest energy levels before moving to higher ones.

Step 2: Analyzing Orbital Diagram (b)

The diagram shows two orbitals, the first with a pair of electrons (spin up and down), and the second and third with one electron (both spin up). This follows the Aufbau principle, as it starts filling the lowest energy orbitals first.

Step 3: Analyzing Orbital Diagram (c)

Diagram (c) also has a pair of electrons in the first orbital, and then one electron each in the next three orbitals (all spin up). This violates the Aufbau principle as higher orbitals seem to be filled prematurely, without completing the second lower energy orbital.

Step 4: Conclusion

Orbital diagram (c) violates the Aufbau principle because all orbitals at a certain energy level must be half-filled before moving to the next energy level, and this rule is not being followed.

Key Concepts

Electron Configuration

Electron configuration is the way we describe how electrons are arranged in an atom. Each electron occupies a specific region around the nucleus known as an orbital. The positioning of electrons follows a specific order based on increasing energy levels. This helps predict the properties and chemical behaviors of an atom.

When writing electron configurations, we start filling the lowest energy orbitals first, following the sequence provided by the Aufbau principle. It's essential to follow the sequence correctly to provide the most stable and accurate picture of how an atom's electrons are distributed.

• The general format displays the principal energy level and the type of orbital (s, p, d, or f).
• The number of electrons in those orbitals is noted as a superscript.

For example, the electron configuration of carbon is written as: \(1s^2 2s^2 2p^2\).

By adhering to proper electron configurations, we can better understand how atoms form bonds and interact with each other.

Orbital Diagram

Orbital diagrams provide a visual representation of the electron configuration of an atom. These diagrams use boxes to represent orbitals within an atom, and arrows to denote the spin of electrons within those orbitals.

Constructing an orbital diagram involves placing electrons into their designated orbitals following specific rules like the Aufbau principle, Hund’s rule, and the Pauli exclusion principle.

• The Aufbau principle instructs filling orbitals from the lowest available energy level first.
• Hund’s rule states that every orbital in a subshell gets one electron before any gets a second, and all electrons in singly occupied orbitals have the same spin.
• The Pauli exclusion principle indicates that no two electrons in the same atom can have identical quantum numbers, meaning that an orbital can hold a maximum of two electrons with opposite spins.

By following these principles, orbital diagrams help visualize the sequential filling of electrons in an atom's orbitals.

Energy Levels

Energy levels, or electron shells, are layers around the atom's nucleus where electrons with similar energy reside. They are organized into principal quantum levels denoted by numbers like 1, 2, 3, and so on. Each level holds a set of orbitals grouped by their energy and shape (s, p, d, f).

As electrons fill up these energy levels, they follow low to high energy order, adhering to the Aufbau principle. This means before occupying a higher energy orbital, electrons will fill up all the lower ones. For example, the electrons will fill the 1s orbital before the 2s, and so forth.

An accurate understanding of these energy levels is crucial because:

• They determine an atom's electron configuration.
• They establish an atom’s chemical properties and reactivity.
• They predict how atoms will interact with each other in chemical reactions.

This knowledge of energy levels is foundational for understanding the rules followed by electrons in orbital filling and the properties of elements.