d-block contraction
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The d-block contraction (sometimes called scandide contraction[1]) is a term used in chemistry to describe the effect of having full d orbitals on the period 4 elements. The elements in question are gallium, germanium, arsenic, selenium, bromine, and krypton[citation needed]. Their electronic configurations include completely filled d orbitals (d10). The d-block contraction is best illustrated by comparing some properties of the group 13 elements to highlight the effect on gallium.
Element | Atomic electron config. | Sum 1st – 3rd | M3+ electron config. | M3+ radius (pm)[1] |
---|---|---|---|---|
Boron, B | [He] 2s2 2p1 | 6887.4 | [He] | |
Aluminium, Al | [Ne] 3s2 3p1 | 5139 | [Ne] | 53.5 |
Gallium, Ga | [Ar] 3d10 4s2 4p1 | 5521.1 | [Ar] 3d10 | 62 |
Indium, In | [Kr] 4d10 5s2 5p1 | 5083 | [Kr] 4d10 | 80 |
Thallium, Tl | [Xe] 4f14 5d10 6s2 6p1 | 5438.4 | [Xe] 4f14 5d10 | 88.5 |
Gallium can be seen to be anomalous. The most obvious effect is that the sum of the first three
Element | Atomic electron config. | Sum 1st – 3rd | M3+ electron config. | M3+ radius (pm)[2] |
---|---|---|---|---|
Boron, B | [He] 2s2 2p1 | 6887.4 | [He] | |
Aluminium, Al | [Ne] 3s2 3p1 | 5139 | [Ne] | 53.5 |
Scandium, Sc | [Ar] 3d1 4s2 | 4256.7 | [Ar] | 74.5 |
Yttrium, Y | [Kr] 4d1 5s2 | 3760 | [Kr] | 90 |
Lanthanum, La | [Xe] 5d1 6s2 | 3455.4 | [Xe] | 103.2 |
Other effects of the d-block contraction are that the Ga3+ ion is smaller than expected, being closer in size to Al3+. Care must be taken in interpreting the ionization potentials for indium and thallium, since other effects, e.g. the inert-pair effect, become increasingly important for the heavier members of the group.
The cause of the d-block contraction is the poor shielding of the nuclear charge by the electrons in the d orbitals. The outer valence electrons are more strongly attracted by the nucleus causing the observed increase in ionization potentials. The d-block contraction can be compared to the lanthanide contraction, which is caused by inadequate shielding of the nuclear charge by electrons occupying f orbitals.
See also
- Periodic table
- Electronegativity
- Electron affinity
- Effective nuclear charge
- Electron configuration
- Exchange interaction
- Lanthanide contraction
References
- ^ "Lanthanide Contraction- D Block Contraction (Scandide Contraction)". chem.libretexts.org. Chemistry Libretexts. August 22, 2020. Retrieved December 6, 2020.
The d block contraction, also known as the Scandide Contraction, describes the atomic radius trend that the d block elements (Transition metals) experience.
- ISBN 978-0-08-037941-8.