Final answer:
Sizes of ions and atoms can be predicted based on electronic structure and charge. Anions like O2- are generally larger than their respective neutral atoms, while cations are smaller due to fewer electrons. Therefore, O2- is larger than Ne, Be is smaller than Mg, Na+ is smaller than Mg2+, and Ba2+ is larger than Xe.
Step-by-step explanation:
To understand which ions or atoms are larger, we should consider not only the number of electron shells, but also the number of electrons and the charge on the ion. Generally, anions (negatively charged ions) are larger than the neutral atoms they come from because the addition of one or more electrons increases electron-electron repulsion within the ion.
On the other hand, cations (positively charged ions) are smaller than their neutral atoms due to the loss of one or more electrons, which decreases electron-electron repulsion and allows the remaining electrons to be pulled closer to the nucleus by the unchanged positive charge.
- O2- is larger than Ne because O2- has gained two electrons, increasing repulsion among electrons and making it larger than a neon atom, which is neutral.
- Be is smaller than Mg because Be is higher up on the periodic table and has fewer electron shells.
- Na+ is smaller than Mg2+ because the removal of electrons in magnesium to form a doubly positive ion allows the remaining electrons to be drawn even closer to the nucleus.
- Ba2+ is larger than Xe because even though both have the same number of electrons, the barium ion has more protons pulling on the same number of electrons, leading to a larger radius for the ion compared to the xenon atom.