How is atomic radius defined in the context of atomic size?

• A. Ionization energy
• B. Atomic radius
• C. Electronegativity
• D. Valence electrons

Answer: (B)

Atomic radius measures how large an atom is, reflected by how far the electron cloud extends from the nucleus. In practice, it is defined as half the distance between the nuclei of two identical atoms that are covalently bonded in a molecule. That bond length arises from how the shared electron density places the nuclei at a certain separation, so each atom contributes roughly half of the total distance. This definition makes it a convenient standard for comparing sizes, though in different contexts you may hear about covalent radius, metallic radius, or van der Waals radius, which adjust the boundary to reflect bonding or close-contact interactions. Ionization energy, electronegativity, and valence electrons describe energy or bonding tendencies rather than the actual size, so they aren't used to define atomic radius.