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Question: What is the correct order of atomic/ionic size?...

What is the correct order of atomic/ionic size?

A

Cu+^+ < Cu < Zn2+^{2+} < Ag

B

Zn2+^{2+} < Cu+^+ < Cu < Ag

C

Ag < Cu < Cu+^+ < Zn2+^{2+}

D

Cu+^+ < Zn2+^{2+} < Cu < Ag

Answer

Zn2+^{2+} < Cu+^+ < Cu < Ag

Explanation

Solution

The correct order of atomic/ionic size can be determined by considering the following principles:

  1. Cation vs. Parent Atom: A cation is always smaller than its parent neutral atom because the loss of electrons reduces electron-electron repulsion and increases the effective nuclear charge, pulling the remaining electrons closer to the nucleus.
    Therefore, Cu+^+ < Cu.

  2. Isoelectronic Ions: For isoelectronic species (those with the same number of electrons), the size decreases as the nuclear charge (number of protons) increases. This is because a higher nuclear charge pulls the electron cloud more strongly towards the nucleus.

    • Cu+^+ has 29 protons and 28 electrons ([Ar] 3d10^{10}).
    • Zn2+^{2+} has 30 protons and 28 electrons ([Ar] 3d10^{10}).
      Since Zn2+^{2+} has a higher nuclear charge than Cu+^+ while having the same number of electrons, Zn2+^{2+} is smaller than Cu+^+.
      Therefore, Zn2+^{2+} < Cu+^+.

  3. Elements in the Same Group: Atomic size generally increases down a group in the periodic table due to the addition of new electron shells.

    • Cu is in Period 4, Group 11.
    • Ag is in Period 5, Group 11.
      Since Ag is below Cu in the same group, Ag is larger than Cu.
      Therefore, Cu < Ag.

Combining the relationships:

  • From (1) and (2): Zn2+^{2+} < Cu+^+ < Cu
  • From (3): Cu < Ag

Putting all these together, the complete order of increasing size is:
Zn2+^{2+} < Cu+^+ < Cu < Ag