Catálogo de publicaciones - libros

Trace elements of the Group 14 are: silicon (Si), germanium (Ge), tin (Sn) and lead (Pb). Silicon, in combination with oxygen, is the basic non-metallic component of all rocks and is considered as a trace element only in respect to its biochemical role. It is the second most abundant element in the lithosphere. It performs an important role in connective tissues, especially in bone and cartilage and it is believed to have played, together with carbon, the crucial function in processes of the first synthesis of proteins (Sedlak 1967). The next three elements, Ge, Sn, and Pb are metals, which show chalcophilic properties and occur in the environment in two oxidation states, +2 and +4 (Table II-14.1).

The Group 15 is composed of semi-metallic elements including arsenic (As), antimony (Sb) and bismuth (Bi). The elements have similar structure and the same symmetry and some similar properties (Table II-15.1). Due to decreased electronegativity, proper metallic character has not been bestrode on As and Sb for which they are often referred to as metalloid which means that these elements have both properties of metals and non-metals. In many ways, As is similar to phosphorous (P), especially in aerated systems.

The Group 16 of the Periodic Table is composed of only two stable trace elements: selenium (Se) and tellurium (Te) which resemble S in a number of geochemical properties, however their behavior in the environment is more complex. Polonium (Po), a natural isotope of the U-Ra transformation chain also belongs to this group.

The Group 17 of the Periodic Table is composed of three trace elements: fluorine (F), bromine (Br), and iodine (I). To this group of elements, called halogens, belongs also chlorine (Cl) which is relatively common in the biosphere, but some authors have treated it as a trace element. Iodine is the least reactive of the elements in this group. The last element of this group, astatine (At), occurs as unstable radioactive isotope of very short lives (the longest half-life of At is 8.1 h).