Rank the following atoms in order of increasing ionization energy, from lowest to highest: S, Se, O, Ne, He

Ionization energy generally increases across a period (from left to right) on the periodic table and decreases down a group (from top to bottom). This is because as you move across a period, the number of protons in the nucleus increases, which increases the positive charge and thus the attraction for the electrons. As you move down a group, the number of energy levels increases, which means the outermost electrons are further from the nucleus and are thus less strongly attracted to it.

Given this, the order of increasing ionization energy for the atoms S (Sulfur), Se (Selenium), O (Oxygen), Ne (Neon), and He (Helium) would be:

Se < S < O < Ne < He

Selenium (Se) has the lowest ionization energy because it is furthest down the periodic table. Sulfur (S) is next, followed by Oxygen (O). Neon (Ne) has a higher ionization energy than Oxygen because it is to the right of Oxygen on the periodic table. Finally, Helium (He) has the highest ionization energy because it is furthest to the right on the periodic table (ignoring the noble gases).