Final answer:
The atomic size is typically referred to as the atomic radius, which is half the distance between the nuclei of two identical bonded atoms in a molecule. This size helps explain how molecules interact and bond.
Step-by-step explanation:
The atomic size generally refers to the size of an atom. It is commonly represented by the concept of atomic radius, which is defined as one-half the distance between the nuclei of two identical atoms that are bonded together. The atomic radius can be difficult to measure precisely because electrons exist around the nucleus in a cloud-like appearance with fuzzy boundaries. Nevertheless, chemists often use the distance between nuclei in diatomic molecules, such as Cl2 or H2, to estimate this value.
One way to express atomic size is by the covalent radius of an atom, which is one-half the distance between the nuclei when two atoms are covalently bonded in a molecule. Although there are multiple ways to define atomic radius, the trend in atomic sizes across the periodic table can be observed, with atomic radius generally decreasing across a period and increasing down a group.