Which atom or ion in the following pairs would you expect to be larger? (c) O-or O2-

Atomic radius refers to the size of an atom, typically measured from the nucleus to the outermost electron shell. As you move down a group in the periodic table, atomic radius increases due to the addition of electron shells. Conversely, across a period, atomic radius generally decreases due to increased nuclear charge, which pulls electrons closer to the nucleus.

Ionic radius is the measure of an atom's ion in a crystal lattice. Cations (positively charged ions) are smaller than their neutral atoms because they lose one or more electrons, reducing electron-electron repulsion and allowing the remaining electrons to be pulled closer to the nucleus. Anions (negatively charged ions), like O2-, are larger than their neutral atoms due to the addition of electrons, which increases electron-electron repulsion.

Electron configuration describes the distribution of electrons in an atom's orbitals. For oxygen, the neutral atom has six electrons, while O2- has eight, achieving a more stable electron configuration similar to that of noble gases. This added stability in anions often results in a larger ionic radius compared to their neutral counterparts, as the additional electrons increase repulsion among them.