Question

In second period of the modern periodic table, two elements X and Y have higher first ionization enthalpy values than the preceding and succeeding elements. X and Y are respectively

• A. B, C
• B. Al, S
• C. Be, N
• D. Na, S

Hint:

The two main exceptions to the increasing trend of first ionization enthalpy across a period occur when removing an electron from a fully-filled s-orbital (Group 2, e.g., Be) and a half-filled p-orbital (Group 15, e.g., N). These configurations are extra stable, requiring more energy for ionization.

Answer 1

The Correct Option is C

To solve the problem regarding ionization enthalpy values in the second period of the periodic table, let's analyze the situation step-by-step:

1. The periodic table is organized in a way that elements with similar properties recur at regular intervals or periods. The second period consists of the elements: Lithium (Li), Beryllium (Be), Boron (B), Carbon (C), Nitrogen (N), Oxygen (O), Fluorine (F), and Neon (Ne).
2. First ionization enthalpy refers to the energy required to remove an electron from an atom in its gaseous state. As we move across a period from left to right, the ionization energy generally increases due to the increasing nuclear charge, which holds the electrons more tightly.
3. However, within this overall trend, there are exceptions. It is known that:
   • Beryllium (Be) has a higher ionization enthalpy than its preceding element, Lithium (Li), and even its successive element, Boron (B), due to its stable filled 2s orbital.
   • Nitrogen (N) also has a higher ionization enthalpy compared to its preceding element, Carbon (C), and its successive element, Oxygen (O), because of its half-filled p subshell, which provides extra stability.
4. These anomalies are explained by electronic configurations: A fully or half-filled subshell offers more stability and thus, requires more energy to remove an electron from such stable configurations. 
5. Therefore, in the second period, elements Beryllium (Be) and Nitrogen (N) have higher ionization enthalpies compared to their neighbors.

Thus, the correct answer is Be, N.