Lanthanide contraction

The lanthanide contraction is the greater-than-expected decrease in atomic radii and ionic radii of the elements in the lanthanide series, from left to right. It is caused by the poor shielding effect of nuclear charge by the 4f electrons along with the expected periodic trend of increasing electronegativity and nuclear charge on moving from left to right. About 10% of the lanthanide contraction has been attributed to relativistic effects.^[1]

A decrease in atomic radii can be observed across the 4f elements from atomic number 57, lanthanum, to 70, ytterbium. This results in smaller than otherwise expected atomic radii and ionic radii for the subsequent d-block elements starting with 71, lutetium.^[2]^[3]^[4]^[5] This effect causes the radii of transition metals of group 5 and 6 to become unusually similar, as the expected increase in radius going down a period is nearly cancelled out by the f-block insertion, and has many other far ranging consequences in post-lanthanide elements.

The decrease in ionic radii (Ln³⁺) is much more uniform compared to decrease in atomic radii.

Element	Atomic electron configuration (all begin with [Xe])	Ln³⁺ electron configuration	Ln³⁺ radius (pm) (6-coordinate)
La	5d¹6s²	4f⁰	103
Ce	4f¹5d¹6s²	4f¹	102
Pr	4f³6s²	4f²	99
Nd	4f⁴6s²	4f³	98.3
Pm	4f⁵6s²	4f⁴	97
Sm	4f⁶6s²	4f⁵	95.8
Eu	4f⁷6s²	4f⁶	94.7
Gd	4f⁷5d¹6s²	4f⁷	93.8
Tb	4f⁹6s²	4f⁸	92.3
Dy	4f¹⁰6s²	4f⁹	91.2
Ho	4f¹¹6s²	4f¹⁰	90.1
Er	4f¹²6s²	4f¹¹	89
Tm	4f¹³6s²	4f¹²	88
Yb	4f¹⁴6s²	4f¹³	86.8
Lu	4f¹⁴5d¹6s²	4f¹⁴	86.1

The term was coined by the Norwegian geochemist Victor Goldschmidt in his series "Geochemische Verteilungsgesetze der Elemente" (Geochemical distribution laws of the elements).^[6]

^ Cite error: The named reference :0 was invoked but never defined (see the help page).
^ Chistyakov, V. M. (1968). "Biron's Secondary Periodicity of the Side d-subgroups of Mendeleev's Short Table". Journal of General Chemistry of the USSR. 38 (2): 213–214. Retrieved 6 January 2024.
^ Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. pp. 536, 649, 743. ISBN 978-0-13-039913-7.
^ Cotton, F. Albert; Wilkinson, Geoffrey (1988), Advanced Inorganic Chemistry (5th ed.), New York: Wiley-Interscience, pp. 776, 955, ISBN 0-471-84997-9
^ Jolly, William L. Modern Inorganic Chemistry, McGraw-Hill 1984, p. 22
^ Goldschmidt, Victor M. "Geochemische Verteilungsgesetze der Elemente", Part V "Isomorphie und Polymorphie der Sesquioxyde. Die Lanthaniden-Kontraktion und ihre Konsequenzen", Oslo, 1925

[:0-1] Cite error: The named reference :0 was invoked but never defined (see the help page).

[Chistyakov-2] Chistyakov, V. M. (1968). "Biron's Secondary Periodicity of the Side d-subgroups of Mendeleev's Short Table". Journal of General Chemistry of the USSR. 38 (2): 213–214. Retrieved 6 January 2024.

[Housecroft-3] Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. pp. 536, 649, 743. ISBN 978-0-13-039913-7.

[Cotton-4] Cotton, F. Albert; Wilkinson, Geoffrey (1988), Advanced Inorganic Chemistry (5th ed.), New York: Wiley-Interscience, pp. 776, 955, ISBN 0-471-84997-9

[Jolly-5] Jolly, William L. Modern Inorganic Chemistry, McGraw-Hill 1984, p. 22

[Goldschmidt-6] Goldschmidt, Victor M. "Geochemische Verteilungsgesetze der Elemente", Part V "Isomorphie und Polymorphie der Sesquioxyde. Die Lanthaniden-Kontraktion und ihre Konsequenzen", Oslo, 1925

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