General Properties of Transition Elements — Revision Notes

⚡ 30-Second Revision

Definition: — Partially filled $(n-1)d$ orbitals in atomic or common ionic state.
Electronic Config: — $(n-1)d^{1-10}ns^{1-2}$ (Exceptions: Cr $3d^54s^1$, Cu $3d^{10}4s^1$).
Oxidation States: — Variable (due to comparable $(n-1)d$ and $ns$ energies).
Colour: — Due to d-d transitions (ions with $d^0$ or $d^{10}$ are colourless).
Magnetic Moment: — $mu = sqrt{n(n+2)}$ BM (n = no. of unpaired electrons).
Lanthanoid Contraction: — Poor shielding by $4f$ electrons $implies$ similar radii for 2nd and 3rd series elements.
Catalysis: — Variable oxidation states, surface area.
Complexes: — Small size, high charge, vacant d-orbitals.
Zn, Cd, Hg: — d-block but NOT true transition elements ($d^{10}$ in common states).

2-Minute Revision

Transition elements, found in the d-block, are defined by having partially filled $(n-1)d$ orbitals in their atomic or common ionic states. This unique electronic structure is the key to their characteristic properties.

They exhibit variable oxidation states because the $(n-1)d$ and $ns$ electrons have similar energies and can both participate in bonding. Most of their compounds are coloured due to d-d electronic transitions, where electrons absorb specific wavelengths of light.

The presence of unpaired d-electrons makes many of them paramagnetic, with the magnetic moment calculated using $mu = sqrt{n(n+2)}$ BM. They are excellent catalysts, often due to their variable oxidation states and ability to form intermediate compounds.

They readily form complex compounds and alloys, and also interstitial compounds. A crucial concept is Lanthanoid Contraction, where the poor shielding of $4f$ electrons leads to a smaller than expected size for elements in the third transition series, making their radii similar to those in the second series.

Remember that Zn, Cd, and Hg are d-block elements but not true transition elements because their d-orbitals are completely filled in their stable ionic states.

5-Minute Revision

Let's consolidate the general properties of transition elements, a high-yield topic for NEET. These elements are defined by having partially filled $(n-1)d$ orbitals in their atomic or common ionic states, with a general electronic configuration of $(n-1)d^{1-10}ns^{1-2}$. Remember the exceptions for Chromium ($[Ar]3d^54s^1$) and Copper ($[Ar]3d^{10}4s^1$).

Their metallic character is pronounced, with high melting points, densities, and good conductivity, attributed to strong metallic bonding involving d-electrons. A key property is variable oxidation states, arising from the close energy levels of $(n-1)d$ and $ns$ electrons, allowing both to participate in bonding. For instance, Manganese shows states from +2 to +7.

Most transition metal compounds are coloured due to d-d transitions. When ligands split the d-orbitals, electrons absorb specific wavelengths of visible light to jump to higher energy d-orbitals, and the complementary colour is observed. Ions with $d^0$ (e.g., $Sc^{3+}$) or $d^{10}$ (e.g., $Zn^{2+}$) configurations are colourless as d-d transitions are not possible.

Many transition metal ions are paramagnetic due to unpaired electrons. The spin-only magnetic moment is calculated as $mu = sqrt{n(n+2)}$ BM, where 'n' is the number of unpaired electrons. For example, $Fe^{3+}$ ($3d^5$) has $n=5$, so $mu approx 5.92$ BM.

Lanthanoid Contraction is vital: the poor shielding of $4f$ electrons leads to a steady decrease in atomic/ionic radii across the lanthanoids, causing elements of the second and third transition series (e.g., Zr and Hf) to have nearly identical sizes. This impacts their chemical similarity and separation.

Transition metals are excellent catalysts (e.g., $V_2O_5$ in Contact process), forming unstable intermediates and providing active surfaces. They readily form complex compounds due to their small size, high charge, and vacant d-orbitals.

They also form interstitial compounds with small non-metals and readily form alloys with each other. Remember the special case of Zn, Cd, and Hg, which are d-block elements but not true transition elements because their d-orbitals are completely filled in their common oxidation states.

Prelims Revision Notes

General Properties of Transition Elements (d-Block)

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Definition: — Elements with partially filled $(n-1)d$ orbitals in their atomic state or any common ionic state.

* Exception: Zn, Cd, Hg are d-block but not true transition elements ($d^{10}$ in common ionic states like $Zn^{2+}$).

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Electronic Configuration: — General: $(n-1)d^{1-10}ns^{1-2}$.

* First Series (Sc-Zn): $3d^{1-10}4s^{1-2}$. * Key Exceptions: * Chromium (Cr): $[Ar]3d^54s^1$ (not $3d^44s^2$) * Copper (Cu): $[Ar]3d^{10}4s^1$ (not $3d^94s^2$)

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Metallic Character: — All are metals. High tensile strength, ductility, malleability, high thermal & electrical conductivity. Strong metallic bonding due to delocalized $ns$ and $(n-1)d$ electrons.

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Atomic & Ionic Radii:

* Across a period: Generally decrease, then become nearly constant, then slightly increase (e.g., for Zn). Less pronounced decrease than s/p-block due to d-electron shielding. * Down a group: Generally increase. * Lanthanoid Contraction: Poor shielding by $4f$ electrons causes the atomic/ionic radii of 2nd and 3rd transition series elements (e.g., Zr/Hf, Nb/Ta) in the same group to be nearly identical. This is a crucial effect.

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Ionization Enthalpy: — Intermediate between s-block and p-block. Generally increases across a period. Irregularities due to $d^5$ and $d^{10}$ stability.

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Oxidation States: — Exhibit variable oxidation states (e.g., Mn: +2 to +7). This is due to the comparable energies of $(n-1)d$ and $ns$ orbitals, allowing both to participate in bonding. The most common state for 1st series is +2 (loss of $4s$ electrons).

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Magnetic Properties:

* Paramagnetism: Caused by unpaired electrons in $(n-1)d$ orbitals. Attracted to magnetic field. * Diamagnetism: All electrons paired. Repelled by magnetic field. * **Spin-only Magnetic Moment ($mu$):** $mu = sqrt{n(n+2)}$ Bohr Magnetons (BM), where 'n' is the number of unpaired electrons. * Ferromagnetism: Strong magnetism (Fe, Co, Ni).

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Colour of Ions & Compounds: — Most are coloured in solid/solution states.

* Reason: d-d electronic transitions. Ligands split d-orbitals; electrons absorb specific wavelengths of visible light to jump to higher energy d-orbitals. The transmitted light is the observed colour. * Colourless Ions: Those with $d^0$ (e.g., $Sc^{3+}$, $Ti^{4+}$) or $d^{10}$ (e.g., $Zn^{2+}$, $Cu^{+}$) configurations, as d-d transitions are not possible.

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Catalytic Properties: — Many act as catalysts (e.g., $V_2O_5$, Fe, Ni).

* Reasons: Variable oxidation states (form unstable intermediates), large surface area (adsorption), ability to form complexes.

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Complex Formation: — Readily form coordination compounds.

* Reasons: Small size, high effective nuclear charge, availability of vacant d-orbitals to accept lone pairs from ligands.

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Interstitial Compounds: — Formed by trapping small non-metal atoms (H, C, N, B) in interstitial voids. Non-stoichiometric, hard, high melting points, retain metallic conductivity.

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Alloy Formation: — Readily form alloys due to similar atomic sizes (e.g., steel, brass, bronze).

Vyyuha Quick Recall

To remember the key properties of Transition Elements, think of VCC-MAFI-CAT:

Variable Oxidation States
Coloured Compounds
Complex Formation
Metallic Character
Alloy Formation
Ferromagnetism (or general Magnetic properties)
Interstitial Compounds
Catalytic Activity
Atomic/Ionic Radii trends (including Lanthanoid Contraction)
Typical Electronic Configuration