Problem 117 - A Complete Resource Book in Chemistry for JEE Main

Question

Properties that are directly or indirectly related to the electronic configuration of the elements and show a regular gradation when we move from left to right in a period or form top to bottom in a group are called periodic properties. Some of these properties are ionization energy, electron affinity and electronegativity Increasing order of second ionization energy is (a) \(\mathrm{Ne}>\mathrm{O}>\mathrm{F}>\mathrm{N}>\mathrm{B}>\mathrm{C}>\mathrm{Be}\) (b) \(\mathrm{Be}<\mathrm{C}<\mathrm{B}<\mathrm{N}<\mathrm{F}<\mathrm{O}<\mathrm{Ne}\) (c) \(\mathrm{Be}<\mathrm{B}<\mathrm{C}<\mathrm{N}<\mathrm{O}<\mathrm{F}<\mathrm{Ne}\) (d) \(\mathrm{B}<\mathrm{C}<\mathrm{N}<\mathrm{O}<\mathrm{F}<\mathrm{Be}<\mathrm{Ne}\)

Step-by-Step Solution

Answer

The increasing order of second ionization energy is option (c) Be < B < C < N < O < F < Ne.

Step 1: Explaining Second Ionization Energy

The second ionization energy is the energy required to remove an electron from an ion with a +1 charge. Elements with stable electron configurations, like those achieving a filled or half-filled shell, tend to have high ionization energies.

Step 2: Order of Second Ionization Energies

Generally, second ionization energy is higher if removing the second electron leads to a stable or noble gas configuration. It increases across a period (left to right on the periodic table) and decreases down a group (top to bottom). It usually reflects the stability of resulting electron configurations after removing two electrons.

Step 3: Analyze Each Element's Configuration

1. Be (1s² 2s²) loses two electrons to become Be²⁺ (a noble gas configuration), very stable. 2. B (1s² 2s² 2p¹). 3. C (1s² 2s² 2p²). 4. N (1s² 2s² 2p³) has half-filled p-orbital after losing, making it stable. 5. O (1s² 2s² 2p⁴). 6. F (1s² 2s² 2p⁵). 7. Ne (1s² 2s² 2p⁶) is a noble gas and very stable.

Step 4: Increasing Order Based on Configuration

From the least to the highest second ionization energy, consider configurations where further ionization pushes them towards or away from stability: Be < B < C < N < O < F < Ne. This order considers the removal of a second electron approaching further stability.

Step 5: Selecting the Correct Answer

Comparing the analyzed order to the options given: The correct sequence that matches our analysis is option (c), which displays the order as Be < B < C < N < O < F < Ne.

Key Concepts

Ionization Energy

Ionization energy refers to the energy required to remove an electron from an atom or ion in its gaseous state. When we speak about the first ionization energy, it involves removing one electron from the neutral atom. The second ionization energy is the energy needed to remove another electron from the ion that already has one positive charge.
For example, the second ionization energy of beryllium (Be) involves removing one electron to form Be²⁺, a configuration resembling a noble gas. It's crucial to recognize that ionization energy is influenced by the electron configuration and the stability of the resulting ion. Noticeably:

• Ionization energy tends to increase across a period from left to right.
• Ionization energy generally decreases as we move down a group.

The increased energy across a period occurs because the electrons are drawn closer to a stronger nuclear charge, making them harder to remove. Conversely, going down a group, electrons lie further away from the nucleus, making them easier to remove.

Electron Configuration

Electron configuration describes the arrangement of electrons within an atom. Electrons populate the atom's energy levels or shells, where inner shells fill first, following the principle of lowest energy first.
This configuration plays a major role in determining an element's chemical properties, including its ionization energy. When an element loses or gains an electron, it adjusts to a more stable electronic structure. For instance:

• Beryllium (Be) has the electron configuration 1s² 2s². When it loses two electrons, it achieves a stable, noble gas configuration.
• Nitrogen (N) possesses a half-filled p-orbital (1s² 2s² 2p³), making it relatively stable.

These configurations help in predicting how easily an atom can undergo ionic changes. The closer an atom is to reaching a stable full or half-full shell, the more stable it becomes. This approach helps explain why elements have varying ionization energies.

Periodic Trends

Periodic trends are recurring patterns observable in the periodic table, related to properties like atomic size, electronegativity, and ionization energy. Understanding these trends can explain the chemical behavior of elements across periods and groups.
Key periodic trends include:

• Ionization Energy: As we move across a period (left to right), ionization energy generally increases due to the increase in nuclear charge holding electrons more tightly.
• Atomic Radius: Atomic size decreases across a period because increased nuclear charge pulls electrons closer, but it increases down a group due to added electron shells.

These trends are essential for predicting how an element will react chemically. They arise due to changes in electron configurations and the interactions between electrons and the nucleus. Recognizing these trends aids in anticipating the chemical reactivities and properties of elements.

Electron Affinity

Electron affinity is the amount of energy released when an electron is added to a neutral atom, forming a negative ion. It's a measure of an atom's ability to accept an electron. Like other periodic properties, electron affinity varies across the periodic table.
Typically, electron affinity becomes more negative across a period, as elements strive to achieve a stable electron configuration. Consider these points:

• Atoms with nearly full valence shells tend to have higher (more negative) electron affinities, as they more readily gain electrons to achieve stability.
• Variation down a group is less predictable. For example, the increased distance from the nucleus can offset other effects, leading to less consistent trends.

Understanding electron affinity helps predict element behavior in reactions, especially for non-metals that tend to gain electrons. It's important for predicting the nature of ions that elements will form.