Summary & Master Memory Capsule

The Whole Chapter in One Glance

The d- and f-block elements owe their family of properties to partially filled d (or f) subshells: variable oxidation states, colour (d-d transitions), paramagnetism (unpaired electrons), catalysis, and complex/interstitial/alloy formation. Two compounds (K$_2$Cr$_2$O$_7$ and KMnO$_4$) are studied in depth, and the f-block is dominated by the lanthanoid contraction and the +3 state.

Slot every fact into one of these branches.

Master Facts Sheet

General config (d-block): $(n-1)d^{1-10}ns^{1-2}$. Exceptions: Cr = $3d^5 4s^1$, Cu = $3d^{10} 4s^1$.

Ions: lose ns before (n-1)d. e.g. Fe$^{3+} = 3d^5$, Mn$^{2+} = 3d^5$, Zn$^{2+} = 3d^{10}$.

Spin-only moment: $\mu = \sqrt{n(n+2)}$ BM (1.73, 2.83, 3.87, 4.90, 5.92 for $n=1$ to 5).

Colour: from d-d transitions; $d^0$ and $d^{10}$ ions are colourless.

Highest oxidation state: up to +7 (Mn); high states appear in oxides/fluorides; +2 grows more stable across the series.

Dichromate (Cr +6): $\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6e^- \rightarrow 2\text{Cr}^{3+} + 7\text{H}_2\text{O}$ (6 e$^-$, equiv mass 49). Acid → orange, base → yellow.

Permanganate (Mn +7): $\text{MnO}_4^- + 8\text{H}^+ + 5e^- \rightarrow \text{Mn}^{2+} + 4\text{H}_2\text{O}$ (acid 5 e$^-$; neutral 3 e$^-$ → MnO$_2$; alkaline 1 e$^-$ → MnO$_4^{2-}$).

Lanthanoid contraction: steady size decrease (poor 4f shielding) → similar 4d/5d radii; lanthanoids mostly +3; actinoids radioactive with more oxidation states.

Quick Comparison Tables

d-block vs f-block

Feature	d-block	f-block
Subshell filled	(n-1)d	(n-2)f
Oxidation states	Many (variable)	Lanthanoids mostly +3
Colour/magnetism	Common	Common (lanthanoids)
Position	Main table groups 3-12	Below the table

Lanthanoids vs Actinoids

Feature	Lanthanoids	Actinoids
Subshell	4f	5f
Common state	+3	Many (up to +6/+7)
Radioactivity	Mostly no	All radioactive
Contraction	Lanthanoid	Actinoid (greater per step)

Last-Minute Memory Hooks

• Cr and Cu exceptions: half-filled $3d^5 4s^1$ and fully-filled $3d^{10} 4s^1$ — the most-tested fact in the chapter.
• Lose ns first when ionising; then count d electrons for unpaired-electron and colour questions.
• $\mu = \sqrt{n(n+2)}$: memorise 1.73, 2.83, 3.87, 4.90, 5.92.
• $d^0$ / $d^{10}$ = colourless and diamagnetic (Sc$^{3+}$, Ti$^{4+}$, Zn$^{2+}$, Cu$^+$).
• Mn = +7 max; high states in oxides/fluorides; +2 grows stable rightward.
• Cu is the odd one out: positive $E^\circ(\text{Cu}^{2+}/\text{Cu})$, no H$_2$ from acids.
• Dichromate = 6 e$^-$ (equiv 49); permanganate = 5 e$^-$ in acid (equiv 31.6); KMnO$_4$ electrons by medium: 5 / 3 / 1.
• Lanthanoid contraction (poor 4f shielding) → similar 4d/5d sizes; +3 dominates; all actinoids radioactive.

One-line revision flow: configurations (Cr, Cu) → sizes & lanthanoid contraction → oxidation states → E values → magnetism & colour → complexes/catalysis/interstitials → dichromate → permanganate → lanthanoids & actinoids.