In this chapter, we learned about the ionization energy (IE) and electron affinity (EA) of atoms. Ionization energy is the energy required to remove an electron from an atom, while electron affinity is the energy change for adding an electron to a gaseous atom to form an anion. We also discussed how these energies vary across a period and down a group in the periodic table.

The IE of an element decreases as the atomic number increases within a period, due to the increasing nuclear charge and the resulting penetration and shielding effects. Similarly, the EA of an element becomes more negative as the atomic number increases within a period, due to the increased effective nuclear charge. However, there are some deviations from these trends, such as the decrease in IE for boron compared to beryllium, despite the greater nuclear charge of boron.

The EA values also show some systematic deviations, such as the rapid increase in EA for Sc and Ga after the third ionization, due to the removal of core electrons. Additionally, we saw that the atom at the top of each group tends to have the most negative EA, which suggests that these atoms have the largest effective nuclear charges.

Overall, the properties discussed in this section are central to understanding chemical reactivity, as they determine the ease with which electrons can be removed from an atom and the resulting metallic character of an element.