What happens to the energy required to remove electrons as the valence shell becomes more filled?

As the valence shell becomes more filled, the energy required to remove electrons increases. This increase can be attributed to the increased electrostatic attraction between the positively charged nucleus and the negatively charged electrons in the valence shell. When there are more electrons in the valence shell, the repulsion among these electrons also plays a role; however, the dominant factor is the increased effective nuclear charge experienced by the outermost electrons. As the outer electrons experience a stronger pull from the nucleus due to more filled electron shells, it becomes more difficult to remove them, thereby necessitating greater energy for ionization.

Consequently, as an atom’s electronegativity increases with a fuller valence shell, the energy required to remove an electron from that atom also increases. This principle is crucial in understanding trends in the periodic table, particularly when analyzing elements across a period or down a group.