The ionic radii of metals are usually

Analysis

This question tests your understanding of atomic structure and the relationship between neutral atoms and their corresponding ions. Specifically, it asks how the size of a metal atom changes when it loses electrons to become a cation.

Concept Explanation

To understand this, we look at two main factors:

1. Electron-Electron Repulsion: In a neutral metal atom, the number of electrons equals the number of protons. When a metal forms an ion, it loses its outermost valence electrons.
2. Effective Nuclear Charge: When electrons are removed, the remaining electrons are held more tightly by the nucleus because the ratio of protons (positive charge) to electrons (negative charge) increases. Furthermore, the loss of an entire outer electron shell significantly reduces the "cloud" of the atom.

Because the remaining electrons are pulled closer to the nucleus and the outermost shell is removed, the resulting ion is always smaller than the neutral atom from which it was formed.

Step-by-Step Solution

1. Identify the process: Metals lose electrons to form positively charged ions (cations). For example, a Sodium atom ($Na$) becomes a Sodium ion ($Na^+$).
2. Compare the structure: • Neutral Atom ($Na$): Has 11 protons and 11 electrons. The electrons occupy three shells. • Cation ($Na^+$): Has 11 protons but only 10 electrons. The loss of the valence electron means the third shell is now empty, leaving only two shells.
3. Evaluate the size: With fewer electrons and one less shell, the electrostatic attraction from the 11 protons pulls the remaining electron cloud much closer to the nucleus.
4. Conclusion: The ionic radius of a metal is always smaller than its atomic radius.

Identifying the Answer

Comparing our conclusion to the options provided:

• A is incorrect because ions are smaller, not larger.
• B is incorrect because the charge directly influences the pull of the nucleus.
• C is incorrect because the loss of electrons changes the size.
• D is correct because the ionic radius is indeed less than the atomic radius.

Exam Tip

Remember the "Shell Loss Rule": When a metal becomes an ion, it loses its outermost shell. Think of it like peeling an orange—if you remove the outer layer, the remaining fruit is smaller! Conversely, non-metals (which gain electrons) form ions that are larger than their atomic radii because the added electrons increase repulsion.