Problem 67 - A Complete Resource Book in Chemistry for JEE Main

Question

The correct order of first ionization potential is (a) \(\mathrm{F}>\mathrm{He}>\mathrm{Mg}>\mathrm{N}>\mathrm{O}\) (b) \(\mathrm{He}>\mathrm{F}>\mathrm{N}>\mathrm{O}>\mathrm{Mg}\) (c) \(\mathrm{He}>\mathrm{O}>\mathrm{F}>\mathrm{N}>\mathrm{Mg}\) (d) \(\mathrm{O}>\mathrm{F}>\mathrm{He}>\mathrm{N}>\mathrm{Mg}\)

Step-by-Step Solution

Answer

Option (b): He > F > N > O > Mg is correct.

Step 1: Understanding Ionization Potential

Ionization potential is the energy required to remove the most loosely bound electron from an isolated gaseous atom to form a cation. Generally, the first ionization potential increases across a period from left to right due to increasing nuclear charge attracting the electrons more strongly.

Step 2: Analyzing Elements Involved

The elements we are considering are He, F, O, N, and Mg. Helium, being a noble gas, has a complete electron shell and thus a very high ionization potential. Fluorine, being highly electronegative with a nearly full valence shell, also has a high ionization potential. Magnesium, being on the left side of the periodic table, has a relatively low ionization potential compared to the others.

Step 3: Comparing Electron Configurations

By looking at the electron configurations, we see that: - He: 1s² - F: 1s² 2s² 2p⁵ (needs only one electron to complete its shell) - O: 1s² 2s² 2p⁴ - N: 1s² 2s² 2p³ (half-filled p sub-shell) - Mg: 1s² 2s² 2p⁶ 3s² A half-filled or fully-filled subshell gives stability, thus N has higher ionization energy than O.

Step 4: Correct Sequence Analysis

According to periodic trends and electronic configurations, Helium is expected to have the highest ionization potential because it's a noble gas. Following He, F will have the next highest ionization potential because it's highly electronegative. Nitrogen, being half-filled, has higher ionization energy than oxygen. So, O should come after N, and Mg, located further left in the periodic table, will have the lowest ionization potential.

Step 5: Selecting the Correct Option

The correct order established from the analysis is He > F > N > O > Mg. This aligns with Option (b).

Key Concepts

Periodic Trends

Periodic trends refer to patterns observed on the periodic table that help in predicting chemical behavior of elements. One key trend is the ionization potential, which generally increases across a period from left to right. This occurs because the nuclear charge, or the positive charge from the nucleus, increases across a period. Consequently, this stronger attraction allows the atom to hold its electrons more tightly, thereby requiring more energy to remove an electron.

However, one must be aware of anomalies. For instance, despite being to the left of oxygen, nitrogen possesses a higher ionization potential due to its half-filled p sub-shell. This stability from half-filling is unique and emphasizes the importance of understanding not just trends, but also underlying electron arrangements.

Overall, by understanding periodic trends, you can predict the behavior of elements in a chemical context which is extremely useful in chemistry.

Electron Configuration

Electron configuration is the arrangement of electrons in an atom's orbitals. It's crucial in determining the chemical properties and reactivity of elements. Each element follows a specific order defined by the Aufbau principle, Hund's rule, and the Pauli exclusion principle, which helps us understand their attributes, such as ionization potential.

Consider helium, with its electron configuration of 1s², making it extremely stable due to a full shell with electrons. Fluorine (1s² 2s² 2p⁵) is one electron short of a full valence shell, contributing to its high ionization potential, as it strongly desires to gain an electron to achieve stability. Magnesium (1s² 2s² 2p⁶ 3s²), on the other hand, has a lower ionization potential due to its relatively less stable electron configuration.

By examining these configurations, we can infer stability and reactivity, which help in predicting the behavior of elements when they interact.

Noble Gases

Noble gases, located in Group 18 of the periodic table, are characterized by having full valence shells of electrons. This configuration makes them extremely stable, with a high ionization potential, as they have no tendency to gain or lose electrons.

Helium, a noble gas, exemplifies this with its electron configuration of 1s². Its full s subshell makes it one of the most inert elements. Despite being the smallest element in terms of atomic size within its group, helium's ionization potential is the highest, a trait common among noble gases, due to their full electron shells.

As a result, noble gases are often used in situations where reactivity needs to be minimized, like in neon signs or providing inert environments for chemical reactions to occur. Understanding noble gases enhances our comprehension of ionization potential and the exceptional stability of full electron shells.

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold electrons within a chemical bond. In the context of first ionization potential, it signifies how strongly an atom attracts its outermost electron, which affects its ability to retain this electron when energy is applied.

Fluorine is a prime example of high electronegativity at work. With its electron configuration of 1s² 2s² 2p⁵, fluorine has a highly attractive nuclear charge, drawing electrons very close and resulting in a high ionization potential. This makes it one of the most electronegative elements on the periodic table, second only to noble gases in stability.

Hence, understanding electronegativity aids in explaining the relationship between an element's position on the periodic table and its ionization potential, assisting in predictions about how elements interact with others in various chemical contexts.