Why is the first ionization energy of Al less than that of Mg and less than that of Si?

The first ionization energy of aluminum (Al) is less than that of magnesium (Mg) because Al has a higher principal quantum number (n=3) compared to Mg (n=2), resulting in greater electron shielding and a weaker attraction between the nucleus and the outer electrons. Additionally, Al has a more complex electron configuration, which introduces repulsion among electrons, further lowering the ionization energy. Compared to silicon (Si), Al has a lower ionization energy due to its position in the Periodic Table, where Si has a stronger nuclear charge and a more stable electron configuration that requires more energy to remove an electron.