Geochem Lecture 6 Crystal structure Part 1 скачать в хорошем качестве

Geochem Lecture 6 Crystal structure Part 1

The basic unit in all crystal structures is Atom. The radius measure depends not only on the nature of the element but also on its state of ionization and the manner in which it is linked to adjacent atoms. The different kinds of inter atomic linkage are classed into 4 bond types as metallic, ionic,covalent, vanderwaals bond. More than one type of bond occurs in a single compound: Heterodesmic If only one bond is present they are known as Homodesmic. For elements in the same group of periodic table the ionic radii increases as the atomic numbers increases. For positive ions of the same electronic structure the radii decreases with increasing charge. For an element that can exist in several valence states i.e from ions of different charge the higher the positive charge on the ion, the smaller the radius. As At.no increases there should be increase in radius. But there is decrease in radius. This is known as Lanthanide contraction. Coordination number of an atom in a molecule is the number of its nearest neighbors. High temperature, low pressure favor low coordination number Low temperature, high pressure favor higher coordination number Radius Ratio: radius of cation/radius of anion