(a) Because an exact outer boundary cannot be measured or even calculated for an atom, how are atomic radii determined? (b) What is the difference between a bonding radius and a nonbonding radius? (c) For a given element, which one is larger? (d) If a free atom reacts to become part of a molecule, would you say that the atom gets smaller or larger?

(a) Atomic radii are determined indirectly by measuring the distance between the nuclei of two bonded atoms of the same element and dividing that distance by two. This is done through methods such as X-ray diffraction or electron microscopy. (b) Bonding radius (covalent radius) is the measure of atomic size when an atom is part of a chemical bond, while nonbonding radius (van der Waals radius) is the measure of atomic size when an atom is not bonded to another atom. (c) The nonbonding radius is generally larger than the bonding radius for a given element, as it represents the entire electron cloud surrounding the nucleus without sharing. (d) When a free atom reacts to become part of a molecule, it generally gets smaller due to the sharing of electrons between the two nuclei leading to a more compact arrangement. However, the size may vary depending on the type of bond and interacting atoms.