Problem 39 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Amongst the following elements (whose electronic configurations are given below), the one having the highest ionization energy is: (a) \([\mathrm{Ne}] 3 s^{2} 3 p^{1}\) (b) \([\mathrm{Ne}] 3 s^{2} 3 p^{3}\) (c) \([\mathrm{Ne}] 3 s^{2} 3 p^{2}\) (d) \([\mathrm{Ne}] 3 d^{10} 4 s^{2} 4 p^{3}\)

Step-by-Step Solution

Answer

(b) \\(\mathrm{[Ne]} 3 s^{2} 3 p^{3}\\).

Step 1: Understand Ionization Energy

Ionization energy is the energy required to remove an electron from an atom. Elements with stable electronic configurations, such as half-filled or fully filled subshells, typically have higher ionization energies because they are more stable.

Step 2: Identify Electronic Configurations

Review the given electronic configurations: (a) \([ ext{Ne}] 3s^2 3p^1\), (b) \([ ext{Ne}] 3s^2 3p^3\), (c) \([ ext{Ne}] 3s^2 3p^2\), (d) \([ ext{Ne}] 3d^{10} 4s^2 4p^3\). These represent elements with sequentially increasing atomic numbers.

Step 3: Recognize Stability of Configurations

Elements with half-filled or fully-filled orbitals are particularly stable. Thus, out of the given configurations, option (b) \([ ext{Ne}] 3s^2 3p^3\) is half-filled and option (d) \([ ext{Ne}] 3d^{10} 4s^2 4p^3\) is also half-filled. These two are of interest.

Step 4: Analyze for Highest Ionization Energy

Between options (b) and (d), option (b) \([ ext{Ne}] 3s^2 3p^3\) corresponds to phosphorus, which has a higher ionization energy compared to the element corresponding to configuration (d), due to its position on the periodic table (higher in energy across a period relates to higher IE).

Step 5: Confirm the Answer

Finally, according to periodic trends: elements further right in the same period or at the top of the periodic table tend to have higher ionization energies. Phosphorus (part of option b) fits this description.

Key Concepts

Electronic Configuration

Electronic configuration is a fundamental concept that helps us understand how electrons are arranged in an atom. Normally, electrons are filled into various energy levels or shells, starting from the lowest energy level and moving upwards. The electrons fill the orbitals in a sequence guided by the Aufbau principle. The order is determined by increasing energy levels of orbitals, which typically follows the pattern of

• s: 2 electrons
• p: 6 electrons
• d: 10 electrons
• f: 14 electrons

An important rule when detailing electronic configuration is that an atom is typically in a stable state when its outer shell is filled or half-filled. Stability is associated with lower energy states, which are achieved when electrons are paired in orbitals. Hence, configurations such as \(3s^2 3p^3\), where \(p\) orbitals are half-filled, result in greater stability due to lower energy content. Understanding the electronic configuration helps in predicting and explaining the properties of elements, such as ionization energy.

Periodic Trends

Periodic trends are patterns observed in the periodic table that help predict the behavior of an element. These trends arise due to the layout of the periodic table, where elements are arranged by increasing atomic number and similar properties in columns (groups). Key periodic trends affecting ionization energy include:

• Moving Across a Period: As you move from left to right across a period, the ionization energy generally increases. This happens because additional protons in the nucleus exert a stronger electrostatic force on the electrons, pulling them closer and requiring more energy to remove one.
• Moving Down a Group: As you move down a column in the periodic table, the ionization energy decreases. This is because the outer electrons are further from the nucleus and are thus more shielded by inner electrons, lessening the nuclear attraction.

These trends enable predictions about the reactivity of elements, including how easily an atom might lose an electron in a chemical reaction. Elements in the upper right corner of the periodic table, like phosphorus in this exercise, tend to have higher ionization energies due to their electronic configuration and positions on the periodic table.

Half-Filled Orbitals

Half-filled orbitals play a crucial role in the stability of elements, which in turn affects their ionization energy. An orbital is considered half-filled when it has an equal number of electrons and available slots. For example, the \(p\) subshell can hold up to 6 electrons, so having 3 electrons results in half-filled stability. The enhanced stability of half-filled orbitals is due to electron exchange energy, which is maximized in such configurations. The electron exchange energy arises from the symmetrical distribution of electrons that minimizes repulsion between them, thus lowering the energy of the atom. Consequently, atoms with half-filled orbitals, like phosphorus with \(3s^2 3p^3\), require more energy to disrupt the balance by removing an electron. That adds to their higher ionization energies compared to other configurations with fewer or more electrons in the same subshell. Recognizing elements with half-filled orbitals is critical for understanding why they might exhibit particular chemical reactivity or stability.