The covalent radius is a measure of the size of an atom that forms part of a covalent bond. It is defined as half the distance between the nuclei of two identical atoms bonded together. This radius helps to understand how closely atoms can approach each other when forming molecules, influencing the overall structure and properties of compounds. Covalent radii vary among different elements and are influenced by factors such as atomic number and electron configuration. For example, elements in the same group of the periodic table, like carbon and silicon, generally have increasing covalent radii due to the addition of electron shells.