Physical Appearance: Silvery white, soft metals, tarnish rapidly in air.
Hardness: Increases with atomic number, Sm is steel-hard.
Melting Points: Range between 1000-1200 K (Sm at 1623 K).
Metallic Structure: Typical metallic structure, good conductors of heat and electricity.
Density: High, no regular trend.
Ionisation Energies: Fairly low, comparable to alkaline earth metals.
Electropositive Character: High due to low I.P.
Complex Formation: Low tendency due to large size and low charge density. $\text{Lu}^{3+}$ is smallest and can form complexes.
Reducing Agent: Readily lose electrons.
Alloy (Misch metals): Lanthanides ($\sim 95\%$) with Fe ($\sim 5\%$), and traces of S, C, Ca, Al.
Basic Nature: $\text{La}(\text{OH})_3$ is most basic, $\text{Lu}(\text{OH})_3$ is least basic.
Carbide: Form MC type carbides with carbon, which on hydrolysis give $\text{C}_2\text{H}_2$.
Eu and Yb dissolve directly in highly concentrated liquid ammonia.

$\text{Ln} + \text{O}_2 \xrightarrow{\text{burns in}} \text{Ln}_2\text{O}_3$
$\text{Ln} + \text{S} \xrightarrow{\text{heated with}} \text{Ln}_2\text{S}_3$
$\text{Ln} + \text{N} \xrightarrow{\text{heated with}} \text{LnN}$
$\text{Ln} + \text{C} \xrightarrow{2773K} \text{LnC}_2, \text{Ln}_2\text{C}_3, \text{Ln}_3\text{C}$
$\text{Ln} + \text{acids} \xrightarrow{\text{with}} \text{H}_2$
$\text{Ln} + \text{halogens} \xrightarrow{\text{with}} \text{LnX}_3$
$\text{Ln} + \text{H}_2\text{O} \xrightarrow{\text{with}} \text{Ln}(\text{OH})_3 + \text{H}_2$

Progressive decrease in size from La to Lu (or $\text{La}^{3+}$ to $\text{Lu}^{3+}$) with increasing atomic number.
Caused by poor shielding effect of $(n-2)f$ electrons.
Enhanced nuclear charge contracts the size of atoms/ions.
Europium and Ytterbium have unexpectedly large atomic volumes due to weaker metallic bonding (they use only two electrons for bonding, like Ba, because of stable $f^7$ and $f^{14}$ configurations).

Close resemblance of Lanthanides: Small increase in ionisation energies, gradual decrease in basic/ionic nature from La to Lu. Explains variations in properties like hydrolysis tendency, complex salt formation, thermal stability.
Similarity of Yttrium with Lanthanides: Yttrium properties are very similar to lanthanides.
Anomalous behaviour of post-lanthanides:
- Atomic size: Ionic radius of $\text{Hf}^{4+}$ is virtually equal to $\text{Zr}^{4+}$ (instead of increasing). This explains similarities between 2nd and 3rd transition series.
- Ionisation potential and electronegativity: Increased IP and electronegativity for 3rd transition series elements due to stronger positive field and tighter electron holding.
- High density: Post-lanthanide elements have very high densities due to compact packing of atoms.

Cerium:
- Ceramic applications: $\text{CeO}_2$, $\text{La}_2\text{O}_3$, $\text{Nd}_2\text{O}_3$, $\text{Pr}_2\text{O}_3$ as decolourizing agents for glasses.
- $\text{CeS}$ (m.p. $\sim 2000^\circ\text{C}$): Used in crucibles and refractories.
- Cerium molybdate, cerium tungstate: Used as paints and dyes.
- Ce salts: Used in textile and leather industries.