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3d Series Elements

Trends in Properties from Scandium (Z=21) to Zinc (Z=30).

By chemca Team • Updated Jan 2026

The 3d series (First Transition Series) involves the filling of the 3d subshell. These elements exhibit characteristic properties due to the presence of unpaired d-electrons.

1. Electronic Configuration

General Configuration: $[Ar] 3d^{1-10} 4s^{1-2}$.

Element	Symbol	Z	Configuration	Note
Scandium	Sc	21	$3d^1 4s^2$	-
Titanium	Ti	22	$3d^2 4s^2$	-
Vanadium	V	23	$3d^3 4s^2$	-
Chromium	Cr	24	$3d^5 4s^1$	Half-filled Stability
Manganese	Mn	25	$3d^5 4s^2$	Half-filled d-subshell
Iron	Fe	26	$3d^6 4s^2$	-
Cobalt	Co	27	$3d^7 4s^2$	-
Nickel	Ni	28	$3d^8 4s^2$	-
Copper	Cu	29	$3d^{10} 4s^1$	Fully-filled Stability
Zinc	Zn	30	$3d^{10} 4s^2$	Not a transition metal

2. Atomic Radii Trends

The Curve

The variation in atomic radii across the 3d series is not uniform.

• Sc to Cr (Decrease): As nuclear charge increases, the shielding by d-electrons is not effective enough to counter it. Radius decreases.
• Mn to Ni (Constant): The increasing nuclear charge is balanced by the screening effect of d-electrons. Radius remains almost constant.
• Cu to Zn (Increase): At the end of the series, electron-electron repulsion in the fully filled d-orbitals dominates over nuclear attraction. Radius increases.

3. Oxidation States

Variable Valency

Transition metals show variable oxidation states because the energy difference between $(n-1)d$ and $ns$ orbitals is very small.

• Common State: +2 (due to loss of $4s^2$). Exception: Sc usually shows +3.
• Highest State: Increases from Sc to Mn, then decreases. The maximum oxidation state is given by the sum of $ns$ and unpaired $(n-1)d$ electrons.
• Manganese: Shows the widest range (+2 to +7).
• Zinc: Only shows +2 (stable $3d^{10}$ configuration).

Common High Oxidation States: $Cr(+6)$ in $Cr_2O_7^{2-}$, $Mn(+7)$ in $MnO_4^-$.

4. Standard Electrode Potentials ($E^\circ_{M^{2+}/M}$)

Irregular Trend

Generally, the values are negative (metals are reducing agents). However, the trend is irregular due to variations in Sublimation Enthalpy, Ionization Enthalpy ($IE_1 + IE_2$), and Hydration Enthalpy.

The Copper Anomaly: Copper has a positive $E^\circ$ value (+0.34 V). This is because the high energy required to remove an electron (high $IE$) is not balanced by its Hydration Enthalpy. Thus, Cu does not liberate $H_2$ from acids.

Mn and Zn: Have more negative $E^\circ$ values than expected due to the stability of half-filled ($d^5$) and fully-filled ($d^{10}$) configurations in the +2 state.

5. Ionization Enthalpy (IE)

Generally increases from left to right due to increased nuclear charge.

• The increase is not as steep as in representative elements due to shielding by d-electrons.
• Exceptions: The $IE_1$ of Zn is very high (stable $d^{10}s^2$). The $IE_2$ of Cr and Cu are unusually high because removal of the second electron disrupts stable $d^5$ and $d^{10}$ configurations.

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