Concept: Ionization Energy Trends in the Periodic Table
Ionization energy is the energy required to remove the most loosely bound electron from an isolated gaseous atom. For the elements Na (Sodium), Mg (Magnesium), Al (Aluminum), and Si (Silicon), which are all in the third period, the ionization energy generally increases across the period from left to right due to increasing nuclear charge. However, there are exceptions due to electron configuration stability.
Step 1: Identify the Atomic Numbers and Electron Configurations
- Na (Z=11): 1s² 2s² 2p⁶ 3s¹
- Mg (Z=12): 1s² 2s² 2p⁶ 3s²
- Al (Z=13): 1s² 2s² 2p⁶ 3s² 3p¹
- Si (Z=14): 1s² 2s² 2p⁶ 3s² 3p²
Step 2: Understand the General Trend and Exceptions
Moving from Na to Si, the nuclear charge increases, which should increase ionization energy. However:
- Mg (3s²) has a stable full s-subshell, so it has higher ionization energy than Al.
- Al (3p¹) has a single electron in the p-orbital, which is easier to remove, so its ionization energy is lower than Mg.
- Si (3p²) has a higher ionization energy than Al due to increased nuclear charge and greater stability with two electrons in the p-orbital.
Thus, the order of ionization energy is: Na < Al < Mg < Si.
Step 3: Match with Given Values
The known ionization energies (in kJ/mol) are:
- Na: 496
- Mg: 737
- Al: 577
- Si: 786
So the correct sequence is 496 (Na), 577 (Al), 737 (Mg), 786 (Si).
Final Answer
The correct option is: 496, 577, 737, 786
Related Topics
- Periodic Trends: Ionization Energy, Electron Affinity, Atomic Radius
- Electron Configuration and Stability
- Exceptions in Period 2 and Period 3 Elements
Formulae and Theory
Ionization energy for the first electron removal is given by:
where is the energy of the neutral atom and is the energy of the cation.
Factors affecting ionization energy:
- Nuclear Charge: Higher nuclear charge increases ionization energy.
- Atomic Size: Larger atoms have lower ionization energy.
- Shielding Effect: Inner electrons shield the outer electrons, reducing ionization energy.
- Stability of Half-filled or Full-filled Orbitals: Atoms with stable configurations have higher ionization energy.
