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d-block contraction (sometimes called scandide contraction) 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 the Ga, Ge, As, Se and bromineBr. Their electronic configurations include completely filled d orbitals (d10). d-block contraction is best illustrated by comparing some properties of the group 13 elements to highlight the effect on gallium.
Gallium can be seen to be anomalous. The most obvious effect is that the sum of the first three ionization potentials of gallium is higher than that of aluminium, whereas the trend in the group would be for it to be lower. The second table below shows the trend in the sum of the first three ionization potentials for the elements B, Al, Sc, Y, La. Sc, Y, La are group 3 elements and have three valence electrons above a noble gas electron core. In contrast to the group 13 elements this sequence shows a smooth reduction.
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 ionisation potentials for indium and thallium, other effects e.g. the inert pair effect become increasingly important for the heavier members of the group.
Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "D-block_contraction". A list of authors is available in Wikipedia.|