What does atomic radius and ionic radius mean?

The atomic radius and ionic radius are measures of the size of atoms and ions, respectively. Here’s a breakdown of each:

Atomic Radius:

The atomic radius is the distance from the nucleus of an atom to the outermost electron shell. It essentially measures the size of an atom.
For atoms, this is typically defined as half the distance between the nuclei of two identical atoms bonded together.
Atomic radius generally decreases from left to right across a period in the periodic table due to increasing nuclear charge, which pulls the electron cloud closer to the nucleus. Conversely, it increases down a group as additional electron shells are added.
Ionic Radius:

The ionic radius refers to the size of an ion, which can be either a cation (positively charged ion) or an anion (negatively charged ion).
When an atom loses electrons to form a cation, the ionic radius is smaller than the atomic radius because the reduced electron-electron repulsion and increased effective nuclear charge pull the remaining electrons closer to the nucleus.
Conversely, when an atom gains electrons to form an anion, the ionic radius is larger than the atomic radius due to increased electron-electron repulsion and a reduced effective nuclear charge.
The ionic radius also varies depending on the charge of the ion: a higher positive charge generally means a smaller ionic radius, while a higher negative charge usually means a larger ionic radius.
In summary, while atomic radius measures the size of an atom, ionic radius measures the size of an ion, reflecting changes in size due to the gain or loss of electrons.