Arsenic pentachloride
Encyclopedia
Arsenic pentachloride is a chemical compound
of arsenic
and chlorine
. This compound was first prepared in 1976 through the UV irradiation of arsenic trichloride
, AsCl3, in liquid chlorine at −105°C. AsCl5 decomposes at around −50°C. The structure of the solid was finally determined in 2001. AsCl5 is similar to phosphorus pentachloride, PCl5 in having a trigonal bipyramidal
structure where the equatorial bonds are shorter than the axial bonds (As-Cleq = 210.6pm, 211.9 pm; As-Clax= 220.7pm).
The pentachlorides of the elements above and below arsenic in group 15, phosphorus pentachloride and antimony pentachloride
are much more stable and the instability of AsCl5 appears anomalous. The cause is believed to be due to incomplete shielding of the nucleus in the elements following the first transition series (i.e. gallium, germanium, arsenic, selenium and bromine) which leads to stabilisation of their 4s electrons making them less available for bonding. This effect has been termed d-block contraction
and is similar to the f-block contraction normally termed the lanthanide contraction
.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
and chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
. This compound was first prepared in 1976 through the UV irradiation of arsenic trichloride
Arsenic trichloride
Arsenic trichloride is an inorganic compound with the formula AsCl3, also known as arsenous chloride or butter of arsenic. This poisonous oil is colourless, although impure samples may appear yellow. It is an intermediate in the manufacture of organoarsenic compounds.-Structure:AsCl3 is a...
, AsCl3, in liquid chlorine at −105°C. AsCl5 decomposes at around −50°C. The structure of the solid was finally determined in 2001. AsCl5 is similar to phosphorus pentachloride, PCl5 in having a trigonal bipyramidal
Trigonal bipyramid molecular geometry
In chemistry a trigonal bipyramid formation is a molecular geometry with one atom at the center and 5 more atoms at the corners of a triangular dipyramid...
structure where the equatorial bonds are shorter than the axial bonds (As-Cleq = 210.6pm, 211.9 pm; As-Clax= 220.7pm).
The pentachlorides of the elements above and below arsenic in group 15, phosphorus pentachloride and antimony pentachloride
Antimony pentachloride
Antimony pentachloride is a the chemical compound with the formula SbCl5. It is a colourless oil, but typical samples are yellowish due to impurities...
are much more stable and the instability of AsCl5 appears anomalous. The cause is believed to be due to incomplete shielding of the nucleus in the elements following the first transition series (i.e. gallium, germanium, arsenic, selenium and bromine) which leads to stabilisation of their 4s electrons making them less available for bonding. This effect has been termed d-block contraction
D-block contraction
d-block 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 Br. Their electronic configurations include completely filled d orbitals...
and is similar to the f-block contraction normally termed the lanthanide contraction
Lanthanide contraction
Lanthanide contraction is a term used in chemistry to describe the decrease in ionic radii of the elements in the lanthanide series from atomic number 58, Cerium to 71, Lutetium, which results in smaller than otherwise expected ionic radii for the subsequent elements starting with 72, Hafnium...
.