The atomic radius represents the size of an atom, while the ionic radius denotes the size of an ion.

The atomic radius is defined as the distance from the nucleus to the outermost electron shell of an atom. It is typically measured in picometers (pm) and varies depending on the specific element. Generally, the atomic radius tends to increase as one moves down a group in the periodic table and decrease as one moves across a period. This trend is primarily attributed to the increasing nuclear charge and the number of electrons in the outermost shell.

In contrast, the ionic radius refers to the distance from the nucleus to the outermost electron shell of an ion. Like the atomic radius, it is also measured in picometers (pm) and its value varies based on the charge of the ion. Cations, which are positively charged ions, possess a smaller ionic radius compared to their parent atoms. This reduction in size occurs due to the loss of electrons, which results in decreased electron-electron repulsion. On the other hand, anions, which are negatively charged ions, exhibit a larger ionic radius than their parent atoms. This increase is due to the gain of electrons, leading to heightened electron-electron repulsion.

In summary, while the atomic radius and ionic radius are related concepts, they are distinct. The atomic radius pertains to the size of an atom, whereas the ionic radius pertains to the size of an ion. The atomic radius typically increases down a group and decreases across a period, while the ionic radius is influenced by the ion’s charge.