Question

Consider the elements Mg, Al, S, P and Si, the correct increasing order of their first ionization enthalpy is :

• A. $Al<Mg<Si<S<P$
• B. $Mg<Al<Si<P<S$
• C. $Mg<Al<Si<S<P$
• D. $Al<Mg<S<Si<P$

Hint:

[Image of Ionization Energy trends in the Periodic Table] Always look for half-filled ($p^3, d^5$) or fully filled ($s^2, p^6$) configurations, as they create "kinks" in the general left-to-right increasing trend of Ionization Enthalpy.

Answer 1

The Correct Option is A

Step 1: Generally, IE increases across a period (Mg to P).
Step 2: Mg ($3s^2$) has a stable fully filled subshell, so its IE is higher than Al ($3s^2 3p^1$).
Step 3: P ($3s^2 3p^3$) has a stable half-filled subshell, so its IE is higher than S ($3s^2 3p^4$).
Step 4: Therefore, the order is Al<Mg<Si<S<P.