Physical Properties — Revision Notes

⚡ 30-Second Revision

Metallic Character: — High, due to s and d electron delocalization.
Melting/Boiling Points: — Generally high, peaks at Group 6 (Cr, Mo, W). Exceptions: Zn, Cd, Hg (low, $d^{10}$ config).
Atomic/Ionic Radii: — Decreases across period, then constant, then slight increase. Increases down group. Lanthanoid Contraction (4f shielding) makes $r_{4d} \approx r_{5d}$ (e.g., Zr/Hf).
Density: — High, increases across period and down group. 5d elements are densest due to lanthanoid contraction.
Enthalpy of Atomization: — High, correlates with melting points, strong metallic bonds.
Magnetic Moment: — $\mu = \sqrt{n(n+2)}$ BM, where 'n' = number of unpaired electrons. Paramagnetic (n>0), Diamagnetic (n=0).
Colour: — Due to d-d transitions (partially filled d-orbitals, $d^1-d^9$) or charge transfer ($d^0, d^{10}$ cases like $MnO_4^-$).

2-Minute Revision

Transition elements are metals with distinct physical properties. They are hard, strong, and have high melting/boiling points due to strong metallic bonding involving both s and d electrons. However, Zn, Cd, and Hg are exceptions with low melting points because their d-orbitals are completely filled, limiting d-electron participation in bonding.

Atomic radii generally decrease across a period but show an anomaly in the 5d series known as lanthanoid contraction, where 4d and 5d elements in the same group have nearly identical sizes (e.g., Zr and Hf) due to poor 4f electron shielding.

This contraction also leads to very high densities for 5d elements. Most transition metal ions are coloured, primarily due to d-d electronic transitions where electrons absorb visible light to jump between split d-orbitals.

Their magnetic properties are often paramagnetic, arising from unpaired d-electrons, and can be quantified using the spin-only formula $\mu = \sqrt{n(n+2)}$ BM.

5-Minute Revision

Transition elements exhibit a fascinating array of physical properties, all rooted in their electronic configuration, particularly the presence of partially filled d-orbitals. They are robust metals, characterized by high tensile strength, malleability, and ductility, stemming from strong metallic bonding where both s and d electrons are delocalized.

This strong bonding also accounts for their generally high melting and boiling points, which peak around Group 6 (Cr, Mo, W) due to the maximum number of unpaired d-electrons. A crucial exception are Zn, Cd, and Hg, which have unusually low melting points because their completely filled $d^{10}$ orbitals prevent d-electron participation in metallic bonding.

Atomic and ionic radii show a general decrease across a period, followed by stabilization, and a slight increase. More significantly, the 5d series elements exhibit 'lanthanoid contraction' – a smaller-than-expected size due to the poor shielding of 4f electrons.

This results in 4d and 5d elements in the same group (like Zr and Hf) having almost identical radii, leading to similar chemistry. This contraction also contributes to the exceptionally high densities of 5d elements.

High enthalpies of atomization further confirm the strength of their metallic bonds.

Most transition metal compounds are coloured, a property explained by d-d transitions. When white light interacts with a complex, electrons in lower energy d-orbitals absorb specific wavelengths and jump to higher energy d-orbitals, with the complementary colour being observed.

This requires partially filled d-orbitals ($d^1-d^9$). For $d^0$ or $d^{10}$ ions (e.g., $MnO_4^-$), colour arises from charge transfer. Finally, their magnetic properties are often paramagnetic due to unpaired d-electrons, quantifiable by the spin-only formula $\mu = \sqrt{n(n+2)}$ Bohr Magnetons (BM), where 'n' is the number of unpaired electrons.

Diamagnetic substances have all paired electrons (n=0).

Prelims Revision Notes

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Metallic Character: — All transition elements are metals. High tensile strength, malleability, ductility, high thermal and electrical conductivity. Due to strong metallic bonding involving both valence s-electrons and unpaired d-electrons.
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Melting and Boiling Points: — Generally high. Maxima at Group 6 (Cr, Mo, W) due to maximum unpaired d-electrons. Exceptions: Zn, Cd, Hg have low melting points due to completely filled $d^{10}$ orbitals, leading to weaker metallic bonds.
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Atomic and Ionic Radii:

* Across a period (3d series): Decreases initially (Sc to Cr/Mn), then relatively constant, then slight increase (Cu, Zn). Due to increasing nuclear charge vs. d-electron shielding. * Down a group: Generally increases. Lanthanoid Contraction: Significant decrease in radii for 5d elements compared to 4d elements in the same group (e.g., Zr and Hf have almost identical radii). Caused by poor shielding of 4f electrons, leading to increased effective nuclear charge.

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Density: — High. Increases across a period (increasing mass, decreasing/constant volume) and down a group (increasing mass, relatively smaller volume due to lanthanoid contraction). 5d elements are exceptionally dense.
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Enthalpy of Atomization: — High values, indicating strong metallic bonding. Trend similar to melting points, peaking at Group 6.
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Magnetic Properties:

* Paramagnetism: Presence of unpaired electrons. Attracted to magnetic field. Calculated by spin-only formula: $\mu = \sqrt{n(n+2)}$ BM, where 'n' is the number of unpaired electrons. * Diamagnetism: All electrons paired (n=0). Weakly repelled by magnetic field (e.g., $Sc^{3+}$ ($d^0$), $Ti^{4+}$ ($d^0$), $Cu^+$ ($d^{10}$), $Zn^{2+}$ ($d^{10}$)).

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Colour: — Most transition metal ions/compounds are coloured.

* d-d transitions: Primary reason. Electrons absorb specific wavelengths of visible light to jump between split d-orbitals. Requires partially filled d-orbitals ($d^1$ to $d^9$). * Charge Transfer: For $d^0$ or $d^{10}$ ions (e.g., $MnO_4^-$ (purple), $Cr_2O_7^{2-}$ (orange)). Electron transfer between ligand and metal.

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Electrical Conductivity: — Excellent conductors due to mobile s and d valence electrons.
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Hardness: — Generally hard and strong, linked to strong metallic bonding.

Vyyuha Quick Recall

To remember the key physical properties of transition metals, think of Many Metals Always Display Excellent Magnetic Colour:

Metallic character (high)
Melting/Boiling points (high)
Atomic/ionic radii (trends, Lanthanoid Contraction)
Density (high)
Enthalpy of atomization (high)
Magnetic properties (paramagnetism, $\mu = \sqrt{n(n+2)}$)
Colour (d-d transitions)