Question

arrange the following elements in order of increasing first ionization energy: al, cl, cs, s, and na.

Explanation:

Step1: Recall ionization - energy trend

Ionization energy increases across a period and decreases down a group in the periodic table.

Step2: Locate elements in periodic table

Cs is in Group 1 and Period 6, Na is in Group 1 and Period 3, Al is in Group 13 and Period 3, S is in Group 16 and Period 3, Cl is in Group 17 and Period 3.

Step3: Analyze based on trends

Cs has the lowest first - ionization energy as it is the largest atom (lowest effective nuclear charge on outer electrons) among them due to being in the lowest period and left - most group. Na is larger than Al, S, and Cl as it is in Group 1. Among Al, S, and Cl in the same period, Al has the lowest first - ionization energy among them as it has a relatively lower effective nuclear charge compared to S and Cl. S has a lower first - ionization energy than Cl because Cl has a higher effective nuclear charge.

Answer:

Cs - 1, Na - 2, Al - 3, S - 4, Cl - 5