Question

of the choices below, which one gives the order of highest to lowest ionization energies? (highest being listed first)
a. cl, s, al, si, ar
b. al, si, s, cl, ar
c. ar, cl, s, si, al
d. cl, s, al, ar, si

Explanation:

Step1: Recall ionization - energy trend

Ionization energy generally increases across a period from left - to - right and decreases down a group. Ar is a noble gas in period 3, which has a very stable electron configuration, so it has the highest ionization energy among these elements. O and S are in group 16, with O having a higher ionization energy than S because the outermost electrons in O are closer to the nucleus. Si and Al are in period 3, with Si having a higher ionization energy than Al as it has more protons in the nucleus attracting the electrons.

Step2: Analyze the options

Based on the above - mentioned trend, the correct order of ionization energies from highest to lowest is Ar > O > S > Si > Al.

Answer:

C. Ar, O, S, Si, Al