Bismuth atom

For the deterrnination of trace amounts of bismuth, atomic absorption spectrometry is probably the most sensitive method. A procedure involving the generation of bismuthine by the use of sodium borohydride followed by flameless atomic absorption spectrometry has been described (6). The sensitivity of this method is given as 10 pg/0.0044M, where M is an absorbance unit the precision is 6.7% for 25 pg of bismuth. The low neutron cross section of bismuth virtually rules out any deterrnination of bismuth based on neutron absorption or neutron activation. 

In a manner similar to phosphoms, arsenic, and antimony, the bismuth atom can be either tri- or pentacovalent. However, organobismuth compounds are less stable thermally than the corresponding phosphoms, arsenic, or antimony compounds, and there are fewer types of organobismuth compounds. For example, with R MX, R3MX2, R2MX3, and RMX, where M is a Group 15 (VA) element and X is a halogen, only the first two types have been prepared where M = Bi, but all four types are known where M = P, As, or Sb. 

Experiments with unsymmetrical iodonium salts iadicate that the bismuth atom is preferentially arylated by the more electron-attracting aryl group. 

The deep violet color of pentaphenylbismuth and certain other pentaarylbismuth compounds has been the subject of considerable speculation. It has been shown by x-ray diffraction (173) that the bismuth atom in pentaphenylbismuth is square—pyramidal. WeU-formed crystals are dichromic, appearing violet when viewed in one plane but colorless in another plane. The nature of the chromophore has been suggested to be a charge-transfer transition by excitation of the four long equatorial bonds ... 

Self-Test 1.12A Write the ground-state configuration of a bismuth atom. 

Some alloys are softer than the component metals. The presence of big bismuth atoms helps to soften a metal and lower its melting point, much as melons would destabilize a stack of oranges because they just do not fit together well. A low-melting-point alloy of lead, tin, and bismuth is employed to control water sprinklers used in certain fire-extinguishing systems. The heat of the fire melts the alloy, which activates the sprinklers before the fire can spread. 

Eulytite. In his investigation of eulytite, Hz4/Sz3012, Menzer3) used the assumption that each bismuth atom should be equidistant from six oxygen atoms. We, however, believe that trivalent bismuth would form three bonds of considerable covalent character, and would hence have as nearest neighbors only three oxygen atoms, at a distance of about 2.17 A. 

Asl3 and Bils. Heyworth and Braekken4) in their studies of the hexagonal crystals Asls and Bils assigned to them structures in which each arsenic or bismuth atom is surrounded by six equidistant iodine atoms, the interatomic distances reported being As—I = 2.97 A and Bi—I = 3.09 A. As in the case of eulytite, we believe that the trivalent atoms are displaced towards three and away from three of these six atoms, until the smallest interatomic distances become As — 7 = 2.54 A and Bi — I = 2.84 A5). 

Bicyclic Systems with Bridgehead (Ring Junction) Phosphorus, Arsenic, Antimony, or Bismuth Atoms... 

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