How does the size of a Ba^{2+} ion compare to the size of a neutral barium atom?

• A. Ba^{2+} is larger than a neutral barium atom.
• B. Ba^{2+} is larger because it has more electrons.
• C. Ba^{2+} and a neutral barium atom are the same size.
• D. Ba^{2+} is smaller than a neutral barium atom.

Answer: (D)

Verified step by step guidance

1. Recall that the size of an atom or ion is often described by its atomic or ionic radius, which depends on the number of electrons and the effective nuclear charge experienced by those electrons.
2. Understand that a neutral barium atom (Ba) has 56 electrons, while the Ba^{2+} ion has lost 2 electrons, leaving it with 54 electrons.
3. Recognize that when electrons are removed to form a cation like Ba^{2+}, the remaining electrons experience a stronger effective nuclear charge because the number of protons (56) remains the same but there are fewer electrons to shield each other.
4. This increased effective nuclear charge pulls the electrons closer to the nucleus, resulting in a smaller ionic radius for Ba^{2+} compared to the neutral Ba atom.
5. Therefore, Ba^{2+} is smaller than the neutral barium atom because it has fewer electrons and a stronger attraction between the nucleus and the remaining electrons.