Atomic / Ionic Radii Trend

Structural Progression: $$\begin{aligned} \text{Sc to Mn:} &\quad \text{Atomic/Ionic Radii Decreases} \\ \text{Fe to Ni:} &\quad \text{Atomic/Ionic Radii Remains Nearly Constant} \\ \text{Cu and Zn:} &\quad \text{Atomic/Ionic Radii Increases Slightly} \end{aligned}$$

Concept: As nuclear charge grows, the electron cloud shrinks; then, a balance between nuclear pull and inner $$d$$-electron shielding stabilizes the atomic size, and lastly, electron-electron repulsions trigger a minor expansion at the very end.

Notation:

• $$\text{Sc to Mn}$$ = Initial contracting phase ($$d^1 \to d^5$$);
• $$\text{Fe to Ni}$$ = Intermediate steady phase ($$d^6 \to d^8$$);
• $$\text{Cu and Zn}$$ = Terminal expansion phase ($$d^{10}$$).