How do the properties of lanthanides change across the series?

The properties of lanthanides change gradually across the series from lanthanum to lutetium. Here’s a overview:

1. Atomic and ionic size:
   • Decreases across the series due to lanthanide contraction (poor shielding by 4f electrons).
2. Density:
   • Increases gradually because the atoms get smaller but the mass increases.
3. Melting and boiling points:
   • Generally increase slightly across the series, but the trend is not perfectly smooth.
4. Electronegativity:
   • Slightly increases across the series as atomic size decreases.
5. Oxidation state:
   • Mostly +3, but a few elements (like cerium, europium, and ytterbium) can show +2 or +4 due to stability of certain electron configurations.
6. Reactivity:
   • Decreases slightly across the series as the atoms become smaller and more tightly bound.
7. Complex formation:
   • Ability to form complexes slightly decreases with decreasing ionic size.

In short: Across the lanthanide series, size decreases, density increases, melting points rise slightly, and reactivity gradually decreases, but all lanthanides generally have similar chemical behavior because of their +3 oxidation state.