Problem 31 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the electronic configuration represents a noble gas? (a) \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{6}\) (b) \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 p^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{3}\) (c) \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{1}\) (d) \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{4}\)

Step-by-Step Solution

Answer

Option (a) represents a noble gas.

Step 1: Understanding Noble Gases

Noble gases have complete electron shells, which usually means their outer shell is filled. In periodic table terms, they have fully occupied s and p orbitals in their highest energy level.

Step 2: Analyzing Option (a)

The configuration given is: \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{6}\). Here, the 3p orbital is fully filled with 6 electrons indicating a stable, full outer shell typical of noble gases (specifically, Argon).

Step 3: Analyzing Option (b)

The configuration given is: \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{3}\). The 3p orbital contains only 3 electrons, meaning it is not fully filled. This configuration does not represent a noble gas.

Step 4: Analyzing Option (c)

The configuration given is: \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{1}\). The 3p orbital is not fully filled, with just 1 electron, so this does not represent a noble gas.

Step 5: Analyzing Option (d)

The configuration given is: \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{4}\). The 3p orbital here has 4 electrons, which means it is partially filled and does not represent a noble gas.

Step 6: Final Step: Conclusion

From the given configurations, option (a) has a full outer shell with the \(3p\) orbital filled with 6 electrons, indicating it matches the configuration of a noble gas, specifically Argon.

Key Concepts

Electronic Configuration

In chemistry, the term "electronic configuration" refers to the arrangement of electrons in an atom's orbitals. Understanding electronic configuration is essential to grasp how elements interact and react to form compounds. Each orbital can hold a specific number of electrons:

• The s orbital can hold up to 2 electrons.
• The p orbital can hold up to 6 electrons.
• The d and f orbitals can hold 10 and 14 electrons, respectively, but are more pertinent in complex atoms.

The configurations are generally written following the Aufbau principle — filling orbitals from lower to higher energy levels. It's also guided by two other rules:

• Pauli Exclusion Principle: No two electrons in an atom can have the same four quantum numbers, effectively allowing only two electrons per orbital with opposite spins.
• Hund's Rule: Electrons will fill empty orbitals of the same energy before doubling up in an orbital.

These guidelines help predict the placement and behaviors of electrons, which is pivotal in identifying the properties of elements.

Periodic Table

The periodic table is an organized chart of chemical elements arranged by atomic number, electron configurations, and recurring chemical properties. Each element is placed based on its atomic number, allowing scientists and students to infer various properties from its position.
The layout of the periodic table shows elements in rows called periods and columns called groups or families:

• Periods: Elements in the same row have the same number of energy levels or electron shells.
• Groups: Elements in the same column have similar valence electron configurations, hence similar chemical behaviors.

The periodic table's design allows for the prediction of an element's properties based on its location. For example, noble gases occupy Group 18, characterized by their complete outer electron shells, making them relatively non-reactive compared to other elements.

Noble Gases

Noble gases are a unique group of elements found in Group 18 of the periodic table. This group includes helium, neon, argon, krypton, xenon, and radon. They are characterized by their full valence electron shells, which typically renders them inert.
Here are some fascinating properties of noble gases:

• They have complete outer s and p valence electron shells, which makes them stable and unlikely to partake in chemical reactions.
• Due to their stability, they are non-flammable and have no color, odor, or taste under standard conditions.
• Noble gases are used in various applications, such as helium in balloons or neon in lighting, due to their low reactivity and unique luminescent properties.

Learning about noble gases introduces students to concepts of chemical stability and electron shell completion, which is pivotal in comprehending how atoms achieve stable configurations like those of noble gases.