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In condensed matter physics and inorganic chemistry, the cation-anion radius ratio can be used to predict the crystal structure of an ionic compound based on the relative size of its atoms. It is defined as the ratio of the ionic radius of the positively charged cation to the ionic radius of the negatively charged anion in a cation-anion compound.
For typical ionic solids, the cations are smaller than the anions, and each cation is surrounded by coordinated anions which form a polyhedron.The sum of the ionic radii determines the cation-anion distance, while the cation-anion radius ratio + / (or /) determines the coordination number (C.N.) of the cation, as well as the shape of the coordinated polyhedron of anions.
Although the tetrahedron is a common coordination geometry for silicon(IV) compounds, silicon may also occur with higher coordination numbers. For example, in the anion hexafluorosilicate SiF 2− 6, the silicon atom is surrounded by six fluorine atoms in an octahedral arrangement. This structure is also seen in the hexahydroxysilicate anion Si ...
In these the locations of the anions and cations are reversed relative to fluorite (an anti-structure); the anions occupy the FCC regular sites whereas the cations occupy the tetrahedral interstitial sites. For example, magnesium silicide, Mg 2 Si, has a lattice parameter of 6.338 Å with magnesium cations occupying the tetrahedral interstitial ...
4, it is usually assumed that the cation is the reactive agent and this tetrahedral anion is inert. BF − 4 owes its inertness to two factors: (i) it is symmetrical so that the negative charge is distributed equally over four atoms, and (ii) it is composed of highly electronegative fluorine atoms, which diminish the basicity of the anion.
Ionic radius, r ion, is the radius of a monatomic ion in an ionic crystal structure. Although neither atoms nor ions have sharp boundaries, they are treated as if they were hard spheres with radii such that the sum of ionic radii of the cation and anion gives the distance between the ions in a crystal lattice.
Depending on the cation-to-anion ratio, the species can either be reduced and therefore classified as n-type, or if the converse is true, the ionic species is classified as p-type. Below, the tree is shown for a further explanation of the pathways and results of each breakdown of the substance.
In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are arccos (− 1 / 3 ) = 109.4712206...° ≈ 109.5° when all four substituents are the same, as in methane ( CH 4 ) [ 1 ] [ 2 ] as well as its heavier analogues .