lanthanide contraction

(noun)

The progressive decrease in the radii of atoms of the lanthanide elements as the atomic number increases; evident in various physical properties of the elements and their compounds.

Related Terms

Examples of lanthanide contraction in the following topics:

  • Lanthanides and Actinides

    • Lanthanides and actinides are elements of the inner transition series of the periodic table.
    • The 14 elements (numbers 58 to 71) of the lanthanide series are also known as the rare earth elements.
    • Most lanthanides are formed when uranium and plutonium undergo nuclear reactions.
    • This phenomenon is known as the lanthanide contraction.
    • All the lanthanide elements exhibit the oxidation state +3.

  • The Bottom of the Periodic Table

    • The atomic number that should be here, 57, is located at the bottom of the table in the row called the Lanthanides.
    • By expanding the horizontal dimensions of the table, the actinide and lanthanide rows can be put into their correct relative positions.
    • In 1934 only 4 actinides were known, all smaller than uranium, so it was not known that they formed a period or family like the lanthanides.
    • The actinides were added along with the lanthanides.
    • The lanthanides and actinides are added as separate but connected rows, building what is called the f-block.

  • Reactions of Coordination Compounds

    • Typically they either have low-charge (Na+), electrons in d orbitals that are antibonding with respect to the ligands (Zn2+), or lack covalency (Ln3+, where Ln is any lanthanide).

  • Diamagnetism and Paramagnetism

    • The size of the magnetic moment on a lanthanide atom can be quite large, as it can carry up to seven unpaired electrons, in the case of gadolinium(III) (hence its use in MRI).

  • General Trends in Chemical Properties

    • The f block, usually offset below the rest of the periodic table, includes the lanthanides and actinides.

  • Variation of Physical Properties Across a Period

    • However, in the d-block, trends across periods become significant, and the f-block elements show a high degree of similarity across periods (particularly the lanthanides).

  • Fused Benzen Ring Compounds

    • Larger fullerenes are found to encapsulate lanthanide metal atoms.

  • Coordination Number, Ligands, and Geometries

    • Due to their large size, lanthanides, actinides, and early transition metals tend to have high coordination numbers.

  • Charles' and Gay-Lussac's Law: Temperature and Volume

    • If a gas contracts by 1/273 of its volume for each degree of cooling, it should contract to zero volume at a temperature of –273°C; this is the lowest possible temperature in the universe, known as absolute zero.
    • The lower a gas' pressure, the greater its volume (Boyle's Law), so at low pressures, the fraction \frac{V}{273} will have a larger value; therefore, the gas must "contract faster" to reach zero volume when its starting volume is larger.
    • This model contains gas molecules on the left side and a barrier that moves when the volume of gas expands or contracts, keeping the pressure constant.

  • Prostaglandins

    • They can lower gastric secretions, stimulate uterine contractions, lower blood pressure, influence blood clotting and induce asthma-like allergic responses.