Solids Flashcards
(35 cards)
Coordination of both cubic and hexagonal close packing?
12
Types of cubic close packed structures?
Face centred cubic
Primitive cubic
Body centred cubic
Fcc
atoms on each of the faces of the cube in addition to each of the eight vertices. Coordination number of 12.
Primitive
Atoms only on the vertices. Coordination number of 6, not close packed. Example of polonium.
Body centred
Atoms on vertices and one in the centre of he cube. Coordination number of 8, not close packed. Examples include sodium and potassium.
How many atoms contribute to the vertex and face in the cubic close packed unit cell?
Vertex 8 - share of 1/8 in the unit cell so contribute 8 x 1/8 to the unit cell
Face 6 - share of 1/2 in the unit cell so contribute 6 x 1/2 to the unit cell
Where do octahedral interstitials occur?
Lie between a triangle of atoms in the row love and another triangle of atoms in the two below
Where do tetrahedral interstitials occur?
Lie between a triangle of atoms in one row and a single atom in the other
Sodium chloride structure coordination numbers?
Both anions have coordination number of 6 and both have octahedral geometries, cubic close packed structure. Most group 1 halides have this structure and many oxides such as magnesium oxide and iron disulphide.
Fluorite structure coordinations numbers?
Based on cubic close packed, each Ca2+ has a coordination number of 8 in a cubic environment, each F- has a coordination number of 4 and is in a tetrahedral environment. Contains 4 Ca2+ ions and 8 F- ions, zirconium (IV) oxide and barium chloride adopt this structure.
Antifluorite is where the anions and cations switch place examples include sodium oxide and silver sulphide.
Nickel Arsenide structure coordination numbers?
Also called nickelling, based on hexagonal close packing, both nickel arsenic atoms have coordination number of 6 with nickel atoms having octahedral geometry, and trigonal prismatic around the arsenic atoms. Examples include cobalt (II) selenide, and nickel (II) telluride.
Spahlerite and wurtzite information?
Polymorphs of ZnS. Sphalerite is based on cubic close packing, wurtzite based on hexagonal close packing. In both cases the ions have coordination numbers of 4 and have tetrahedral geometry. Copper(I) chloride and silver(I) iodised adopts sphalerite. Zinc oxide, silicon carbide and boron nitride all adopt wurtzite structures.
Cadmium chloride and cadmium iodide information?
CdCl2 based on cubic close packing, CdI2 based on hexagonal close packing. Cd2+ ions with a coordination of 6 have octahedral geometry and fill alternating layers of octahedral sites, both form layered structures. The halide ions have a coordination number of 3 and trigonal pyramidal geometry.
Magnesium chloride and tantalum sulfide ave CdCl2 structuren. Lead(II) iodide and iron(II) bromide form the CdI2 structure.
Caesium chloride information?
Based on primitive close packing, all interstitial sites are equivalent. Have cubic geometry. Coordinations our both ions are 8. Formed by halides of singly charged cations, caesium bromide, thallium chloride.
Rutile information?
Polymorph of titanium dioxide, unit cell not cubic, titanium ions have coordination number of 6 with distorted octahedral geometry, oxide has coordination number of 3 and adopt trigonal planar geometries.
Perovskite structure A information?
CaTiO3, two possible structures. One potential is a primitive cubic Ca2+ on vertices, O2- on faces and Ti4+ in the centre. Ca2+ hs 8 atoms in unit cells, shares 1/8 to unit cell so total contribution is 1/8 x 8, Ti4+ has 1 atom in unit cell, and has a contribution of 1 to the unit cell, O2- has 6 atoms in the unit cell, shares 1/2 so contributes 6 x 1/2 to the unit cell.
Perovskite structure B information?
Described as primitive close packing of Ti4+ ions on the vertices, O2- anions on the edges and Ca2+ ion in the centre.
Ti4+ hs 8 atoms in unit cells, shares 1/8 to unit cell so total contribution is 1/8 x 8, Ca2+ has 1 atom in unit cell, and has a contribution of 1 to the unit cell, O2- has 12 atoms in the unit cell, shares 1/4 so contributes 12 x 1/4 to the unit cell.
Radius ratio rule?
r+/r-
Linear radius ratio?
< 0.155
Trigonal radius ratio?
0.155 - 0.225
Tetrahedral radius ratio?
0.225 - 0.414
Octahedral radius ratio?
0.414 - 0.732
Cubic radius ratio?
0.732 - 1.000
Cuboctahedral radius ratio?
> 1.000
