Question

The first ionization potential of Na, Mg, Al and Si are in the order:

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

Answer 1

The correct option is A

Na < Mg > Al < Si

Na, Mg, Al and Si are the elements of the period II. The ionization potential increases across the period from left to right. Al has lower ionization potential than Mg because Al has one unpaired electron in it's highest energy orbital (3p), and in Mg's highest energy orbital (3s) the electrons are paired. It is energetically favourable for all the electrons in an orbital to be paired, which means that breaking up this pair would require more energy.