![d-block contraction--EN](https://upload.wikimedia.org/wikipedia/commons/a/aa/D-block_contraction--EN.png)
The 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
Period may refer to:
Common uses
* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
4 elements. The elements in question are
gallium,
germanium,
arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, ...
,
selenium
Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
,
bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
, and
krypton
Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often ...
. Their electronic configurations include completely filled d orbitals (d
10). The d-block contraction is best illustrated by comparing some properties of the
group 13 elements
The boron group are the chemical elements in periodic table group, group 13 of the periodic table, comprising boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl), and nihonium (Nh). The elements in the boron group are characterize ...
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 potential
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...
s 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, and
La.
Sc,
Y, and
La have three valence electrons above a
noble gas
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low ch ...
electron core. In contrast to the
group 13 elements
The boron group are the chemical elements in periodic table group, group 13 of the periodic table, comprising boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl), and nihonium (Nh). The elements in the boron group are characterize ...
, this sequence shows a smooth reduction.
Other effects of the d-block contraction are that the Ga
3+ ion is smaller than expected, being closer in size to Al
3+. Care must be taken in interpreting the
ionization potentials for
indium
Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
and
thallium
Thallium is a chemical element with the symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists William Crookes an ...
, since other effects, e.g. the
inert pair effect The inert-pair effect is the tendency of the two electrons in the outermost atomic ''s''-orbital to remain unshared in compounds of post-transition metals. The term ''inert-pair effect'' is often used in relation to the increasing stability of ox ...
, 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
The lanthanide contraction is the greater-than-expected decrease in atomic radii/ionic radii of the elements in the lanthanide series from atomic number 57, lanthanum, to 71, lutetium, which results in smaller than otherwise expected atomic radii ...
, which is caused by inadequate shielding of the nuclear charge by electrons occupying f orbitals.
See also
*
Periodic table
*
Electronegativity
Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...
*
Electron affinity
The electron affinity (''E''ea) of an atom or molecule is defined as the amount of energy released when an electron attaches to a neutral atom or molecule in the gaseous state to form an anion.
::X(g) + e− → X−(g) + energy
Note that this is ...
*
Relativistic quantum theory
In theoretical physics, quantum field theory (QFT) is a theoretical framework that combines classical field theory, special relativity, and quantum mechanics. QFT is used in particle physics to construct physical models of subatomic particles and ...
*
Effective nuclear charge In atomic physics, the effective nuclear charge is the actual amount of positive (nuclear) charge experienced by an electron in a multi-electron atom. The term "effective" is used because the shielding effect of negatively charged electrons prevent ...
*
Electron configuration
*
Exchange interaction
In chemistry and physics, the exchange interaction (with an exchange energy and exchange term) is a quantum mechanical effect that only occurs between identical particles. Despite sometimes being called an exchange force in an analogy to classic ...
*
Lanthanide contraction
The lanthanide contraction is the greater-than-expected decrease in atomic radii/ionic radii of the elements in the lanthanide series from atomic number 57, lanthanum, to 71, lutetium, which results in smaller than otherwise expected atomic radii ...
References
*{{Greenwood&Earnshaw
Chemical bonding
Atomic radius