Radical
A radical is an atom of an element or a group of atoms of different elements that behave as a single unit with a positive or negative charge on it.
Positively charged radicals are called basic
radicals such as Na+, NH4+ etc.
Negatively charged radicals are called acid
radicals such as NO3-, Cl-, etc.
Basic radicals are also known as cations and acid radicals are known as anions.
Radicals are categorised as monovalent, bivalent, trivalent, etc.