Question:medium
The first ionization enthalpy of Na, Mg and Si, respectively, are : 496, 737 and 786 kJ mol–1. The first ionization enthalpy (kJ mol–1) of Al is:
The first ionization enthalpy of Na, Mg and Si, respectively, are : 496, 737 and 786 kJ mol–1. The first ionization enthalpy (kJ mol–1) of Al is:
Updated On: Mar 25, 2026
- 487
- 768
- 577
- 856
Show Solution
The Correct Option is C
Solution and Explanation
The question asks for the first ionization enthalpy of aluminum (Al), given the first ionization enthalpy values of sodium (Na), magnesium (Mg), and silicon (Si) as 496 kJ mol–1, 737 kJ mol–1, and 786 kJ mol–1, respectively. Let's solve this step-by-step:
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Understanding Ionization Enthalpy:
Ionization enthalpy is the energy required to remove the outermost electron from a gaseous atom in its ground state.
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Periodic Trends in Ionization Enthalpy:
- Generally, ionization enthalpy increases across a period from left to right due to an increase in nuclear charge, which strengthens the attraction between the nucleus and the valence electrons.
- However, there are exceptions due to atomic structure and electron configurations.
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Analyzing the Elements:
- Sodium (Na), Magnesium (Mg), Aluminum (Al), and Silicon (Si) are in the same period of the periodic table.
- Based on the usual trend, ionization enthalpy increases from Na to Mg to Si.
- Aluminum (Al) is positioned between magnesium (Mg) and silicon (Si) in the periodic table.
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Reason for Ionization Enthalpy of Aluminum:
- The configuration of Al is such that its outer electron is in a new orbital (3p1), which requires less energy for removal compared to the filled 3s level of Mg.
- Hence, Al has a lower ionization enthalpy than Mg despite being further to the right on the periodic table.
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Conclusion:
Based on these considerations, the first ionization enthalpy of aluminum (Al) is close to the given value for sodium (Na), but greater.
The correct option is 577 kJ mol–1.
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