Question

The correct order of sccond ionisation potential of \(\mathrm{C}, \mathrm{N}, \mathrm{O}\) and \(\mathrm{F}\) is (1) \(\mathrm{C}>\mathrm{N}>\mathrm{O}>\mathrm{F}\) (2) \(\mathrm{O}>\mathrm{N}>\mathrm{F}>\mathrm{C}\) (3) \(\mathrm{O}>\mathrm{F}>\mathrm{N}>\mathrm{C}\) (4) \(\mathrm{F}>\mathrm{O}>\mathrm{N}>\mathrm{C}\)

Short answer

(4) \(\text{F} > \text{O} > \text{N} > \text{C}\).

Step-by-step solution

Understanding Ionisation Potential

Ionisation potential is the energy required to remove an electron from an atom or ion. The second ionisation potential is the energy needed to remove the second electron after the first has been removed.

Electron Configurations

Write the electron configurations for \(\text{C}, \text{N}, \text{O}, \text{F}\) atoms: \(\text{C}: 1s^2 2s^2 2p^2\), \(\text{N}: 1s^2 2s^2 2p^3\), \(\text{O}: 1s^2 2s^2 2p^4\), \(\text{F}: 1s^2 2s^2 2p^5\).

Configuration After First Ionisation

Determine the configurations after removing the first electron: \(\text{C}^+: 1s^2 2s^2 2p^1\), \(\text{N}^+: 1s^2 2s^2 2p^2\), \(\text{O}^+: 1s^2 2s^2 2p^3\), \(\text{F}^+: 1s^2 2s^2 2p^4\).

Removing the Second Electron

Removing the second electron from these ions: \(\text{N}^+ \text{and} \text{O}^+\) have half-filled and more stable configurations compared to \(\text{C}^+\) and \(\text{F}^+\). Thus, their second ionisation energies will be higher relative to \(\text{C}\) and \(\text{F}\).

Ordering the Ionisation Potentials

Arrange based on ease of second electron removal: \(\text{F} > \text{O} > \text{N} > \text{C}\).

Key concepts

ionisation potential

Ionisation potential refers to the energy required to remove an electron from an atom or ion. It is a key concept in understanding the reactivity and stability of elements. There are multiple ionisation potentials for an element, corresponding to the removal of successive electrons.

The second ionisation potential specifically pertains to the energy necessary to remove the second electron after the first has already been removed. This value is usually higher than the first ionisation potential due to the increased positive charge in the ion, which holds the remaining electrons more tightly.

electron configuration

Electron configuration describes the distribution of electrons in an atom's or ion’s orbitals. Each element has a unique configuration that determines its chemical properties.

For example:

• Carbon (C): 1s² 2s² 2p²
• Nitrogen (N): 1s² 2s² 2p³
• Oxygen (O): 1s² 2s² 2p⁴
• Fluorine (F): 1s² 2s² 2p⁵

When an electron is removed, the configuration changes accordingly. For instance, after removing one electron from Carbon (C), its configuration will be 1s² 2s² 2p¹. Understanding these configurations is crucial for predicting ionisation potentials and other chemical behaviors.

ionisation energy trends

Ionisation energy generally increases across a period (left to right in the periodic table) and decreases down a group (top to bottom).

This is due to:

• Increasing nuclear charge as more protons are added, which pulls the electrons closer and makes them harder to remove.
• Decreasing atomic radius across a period, meaning the electrons are closer to the nucleus.
• Increased electron shielding down a group, which means outer electrons are further from the nucleus and more shielded by inner electrons.

For second ionisation energies, these trends still apply, but the impact is also influenced by the stability of the resulting electron configuration after the first electron is removed.

periodic table

The periodic table is an organized tabular arrangement of elements based on atomic number, electron configurations, and recurring chemical properties.

Important aspects include:

• Groups (vertical columns) indicate elements with similar properties and the same number of valence electrons.
• Periods (horizontal rows) show elements with increasing atomic number and consecutive filling of electron shells.

Understanding how ionisation potentials vary across the periodic table is critical. For example, elements in the same group have similar outer electron configurations but changing ionisation energies due to atomic size and shielding effects.