Rank the following elements in order of increasing first ionization energy: Na, Mg, Al.

• A. Mg < Al < Na
• B. Mg < Na < Al
• C. Al < Mg < Na
• D. Na < Mg < Al

Answer: (D)

Verified step by step guidance

1. Recall that the first ionization energy is the energy required to remove one mole of electrons from one mole of gaseous atoms, and it generally increases across a period from left to right in the periodic table due to increasing nuclear charge.
2. Identify the positions of the elements Na, Mg, and Al in the periodic table: all are in the same period (Period 3), with Na in Group 1, Mg in Group 2, and Al in Group 13.
3. Understand that as you move from left to right across a period, the effective nuclear charge increases, which means electrons are held more tightly, leading to higher ionization energies.
4. Compare the elements: Sodium (Na) has the lowest nuclear charge among the three, so it has the lowest first ionization energy; Magnesium (Mg) has a higher nuclear charge than Na, so its ionization energy is higher; Aluminum (Al) has the highest nuclear charge among the three, so it has the highest first ionization energy.
5. Conclude that the order of increasing first ionization energy is Na < Mg < Al, consistent with the trend of increasing ionization energy across a period.