What term describes the outermost shell of an electron?

The outermost shell of an electron is referred to as the valence shell. This term is crucial in understanding the behavior of electrons in chemical bonding and reactivity. The valence shell is responsible for the chemical properties of an element because it contains the electrons that are involved in bonding with other atoms.

Electrons in the valence shell can be shared or transferred between atoms to form chemical bonds, making it essential for determining how atoms interact. Elements with a full valence shell are typically more stable and less reactive, while those with incomplete valence shells tend to be more reactive as they seek to achieve stability through bonding.

Understanding the valence shell is fundamental in chemistry and helps explain phenomena such as periodic trends, electronegativity, and the formation of covalent and ionic bonds.