Which shell of an atom has the lowest binding energy?

The outer shell of an atom, often referred to as the valence shell, is associated with the lowest binding energy compared to the inner and middle shells. This phenomenon occurs because the outer shell is farther from the nucleus, which means that the protons and neutrons within the nucleus exert a weaker attractive force on the electrons located in the outer shell.

As electrons reside in energy levels further from the nucleus, they are less tightly bound due to the effects of shielding and distance. Shielding occurs when inner shell electrons repel outer shell electrons, effectively reducing the nuclear charge felt by those outer electrons. Consequently, this phenomenon contributes to the reduced binding energy in the outer shell compared to the inner and middle shells, where electrons experience a stronger electrostatic attraction to the positively charged nucleus.

Understanding this concept is critical in fields such as atomic physics and chemistry, as it relates to the behavior of electrons during chemical reactions, the formation of ions, and the absorption/emission of energy in various processes.