Problem 54 - A Complete Resource Book in Chemistry for JEE Main

Question

The first ionization energy in electron volts of nitrogen and oxygen atoms are respectively given by (a) \(14.6,13.6\) (b) \(13.6,14.6\) (c) \(13.6,13.6\) (d) \(14.6,14.6\)

Step-by-Step Solution

Answer

Option (a) 14.6, 13.6.

Step 1: Understand Ionization Energy

Ionization energy is the energy required to remove an electron from a gaseous atom or ion. It generally increases across a period from left to right due to increasing nuclear charge.

Step 2: Compare Nitrogen and Oxygen Positions

Nitrogen and Oxygen are in the second period of the periodic table. Oxygen comes after nitrogen, but due to electron configuration and increased electron-electron repulsions in oxygen, nitrogen actually has a higher first ionization energy.

Step 3: Recall the Exception in Period 2

Normally, ionization energy increases across a period but between nitrogen and oxygen, there is an exception. Nitrogen, with a half-filled p subshell, has a slightly higher ionization energy than oxygen which has one more electron causing repulsion and a drop in ionization energy.

Step 4: Select the Correct Option

Based on the exception, nitrogen has a higher ionization energy than oxygen. Therefore, the answer must reflect nitrogen having a value of 14.6 and oxygen 13.6. This corresponds to option (a).

Key Concepts

Understanding Periodic Table Trends

The periodic table is structured in such a way that it helps us predict various properties of elements, including ionization energy.
As we move from left to right across a period, the ionization energy generally increases. This happens because the atomic radius decreases, thus increasing the nuclear charge, which pulls electrons in closer. This makes it more difficult to remove an electron.

• The electrons are more strongly attracted to the nucleus due to the higher effective nuclear charge.
• Smaller atomic size contributes to a higher ionization energy.

However, there are exceptions, especially within periods where electron configuration plays a crucial role.

Nitrogen vs Oxygen Ionization

The comparison of ionization energies between nitrogen and oxygen provides an interesting exception in periodic trends.
Although typically the ionization energy increases across a period, nitrogen has a higher first ionization energy than oxygen, even though oxygen is to the right of nitrogen in the periodic table.

• Nitrogen's electron configuration results in a half-filled p subshell, which is especially stable.
• Oxygen's additional electron introduces repulsions because it pairs up in the p orbital, which makes it slightly easier to remove than expected.

This is why nitrogen, despite being earlier in the period, has a higher ionization energy than oxygen.

Electron Configuration and Its Impact

Electron configuration is a key player in understanding ionization energies. It describes how electrons are distributed in an atom.
Each electron is found in orbital shells, and the specific distribution impacts properties such as stability and reactivity.

• A stable configuration, such as a half-filled subshell, results in higher ionization energies.
• An added electron in an otherwise stable configuration can cause repulsion, decreasing ionization energy.

For nitrogen, its electron configuration is such that it has a half-filled p subshell, giving it extra stability and thus higher ionization energy than oxygen, which doesn't benefit from such stability.