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) \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{3}\) (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

(a) represents a noble gas configuration.

Step 1: Define a Noble Gas

Noble gases are characterized by having a complete valence shell, making them very stable and non-reactive. This typically means their outer shell configuration is full. For noble gases, the p orbital is completely filled, with 6 electrons.

Step 2: Analyze Configuration (a)

Consider the configuration (a): \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{6}\). The 3p orbital is filled with 6 electrons, indicating a complete outer shell, typical of a noble gas configuration.

Step 3: Analyze Configuration (b)

For configuration (b): \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{3}\). The 3p orbital contains only 3 electrons, which does not indicate a full outer shell.

Step 4: Analyze Configuration (c)

Examine the configuration (c): \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{1}\). Here, the 3p orbital contains only 1 electron. This also does not represent a full outer shell.

Step 5: Analyze Configuration (d)

Check the configuration (d): \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{6}, 3 \mathrm{~s}^{2}, 3 \mathrm{p}^{4}\). The 3p orbital has 4 electrons, which is not a full orbital.

Step 6: Conclude the Noble Gas Configuration

The electronic configuration that represents a noble gas is the one where the outermost p orbital is completely filled, which is configuration (a).

Key Concepts

Electron Configuration

Electron configuration refers to the arrangement of electrons distributed among the various orbitals around the nucleus of an atom. Each element has a unique electron configuration that determines its chemical properties. These configurations are denoted by numbers and letters where numbers indicate energy levels, and letters (s, p, d, f) indicate the type of orbital. In an electron configuration, the superscript shows how many electrons are in each orbital. For example, in the electron configuration \(1s^2 2s^2 2p^6\), the superscript tells us that the 1s orbital contains 2 electrons.

• The order of filling the electrons into these orbitals is governed by the Aufbau principle, starting from the lowest energy level to higher levels.
• Electron configurations help us understand the chemical reactivity and properties of an element.

Understanding electron configurations can aid in identifying the type of element, such as metals, non-metals, and noble gases, based on their stability patterns.

Valence Shell

The valence shell is the outermost shell of an atom in which the valence electrons reside. These electrons are crucial because they determine how an element will react chemically with other elements. The valence shell's capacity to hold electrons is a major factor in an atom's chemical properties.

• For instance, in the electron configuration \(1s^2 2s^2 2p^6 3s^2 3p^6\), the electrons in the 3s and 3p orbitals are in the valence shell.
• Elements with a full valence shell, like noble gases, are typically non-reactive because they have a stable electron arrangement.

The desire of atoms to achieve a full valence shell is the driving force behind chemical bonding, where atoms either lose, gain, or share electrons to reach stable electron configurations similar to those of noble gases.

Stability of Noble Gases

Noble gases are known for their exceptional stability and non-reactivity, which can be attributed to their complete valence electron shells. These elements' electron configuration results in fully filled outermost shells, making them chemically inert.

• For example, Argon has an electron configuration of \(1s^2 2s^2 2p^6 3s^2 3p^6\), with 6 electrons in the 3p orbital, completing its outer shell.
• This complete configuration minimizes energy and maximizes stability, making further electron gain or loss unnecessary.

Because of their stability, noble gases are used in environments requiring non-reactive atmospheres, such as in lighting and welding industries. Their inert nature stems from the lack of tendency to form bonds due to their full electron orbitals.

p Orbital Electron Filling

The filling of electrons into p orbitals follows specific rules to achieve the lowest energy configuration. P orbitals can hold a maximum of six electrons, making them significant in determining an atom's chemical behavior. As electrons fill these orbitals, they adhere to Hund's rule and the Pauli Exclusion Principle to achieve a stable configuration.

• In a p orbital configuration, electrons will first fill an empty orbital before pairing up in a half-filled orbital as seen in, for example, nitrogen (\(1s^2 2s^2 2p^3\)).
• Once a p orbital is fully filled, as in noble gases, the element achieves maximum stability due to the electron pairing and minimized repulsion.

The full filling of the p orbital, especially in the valence shell, leads to a "noble gas configuration," characterized by chemical inertness and stability. The understanding of this concept is crucial for predicting the reactivity and bonding of different elements.