ATOMIC-ENVIRONMENT CLASSIFICATION OF THE CHEMICAL-ELEMENTS

Of the 103 known chemical elements, 96 crystallize in 52 different cry stal structures. Included in these 52 structures are those which are s table under normal (298 K, 100 kPa) conditions (NC) as well as high or low temperature (HT/LT) and high pressure (HP) conditions, but with t he O-, N-, and C-stabilized structures excluded as well as structures observed in thin films. Of the 275 experimentally found and reported e lement modifications, 95% can be classified with just seven different atomic environment types (AETs), all belonging to the single-environme nt type. A single-environment type encompasses all structures in which all atoms present in the structure have the same AET. The seven AETs observed are the octahedron, the cubo-octahedron, the twinned cubo-oct ahedron and the rhombic dodecahedron for metals, and the dumb-bell, th e double link and the tetrahedron for non-metals. With modified struct ural stability diagrams (SSDs) we show that under normal conditions th e elements are simply separated into different AET domains. With the H T/LT and HP crystal structure data included in our SSDs, we predict fo r 31 elements the AET modification (so far unknown) to be found under HP or HT/LT conditions, based on our SSD-AET domains. Finally, our inv estigation includes a comprehensive, critically evaluated crystallogra phic data set for all element modifications as well as a recommended a tomic volume table. These volumes are calculated from the unit cell vo lume divided by the number of atoms per unit cell.