Inorganic Lecture 6

Inorganic Lecture 6 - 1 6th Lecture Today s Topics Ionic...

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Unformatted text preview: 1 6th Lecture Today s Topics Ionic radii Ionic Lattice types Ionic Radii Internuclear distance between a cation and the closest anion in the lattice = r cation + r anion Usual method of determining r + and r- is from the analysis of many internuclear distances obtained experimentally When a set of ionic radii are combined (added) the observed internuclear distance should be found Values differ slightly from one source to another There is a dependence of ionic size on CN r ion increases slightly with increasing CN Radii tell us something about expected coordination spheres 2 Trends in Ionic Radii The cation size increases upon descending groups 1 and 2 The anion size increases upon descending group 17 Only a small variation in size for M 3+ and M 2+ ions of the d-block metals Radius Ratio Rule The radius ratio ( ) can be used to determine the coordination number (geometry) of the ion The must be of a certain value in order for a certain coordination geometry to be present geometry CN# cubic 8 >0.7 octahedral 6 0.4 - 0.7 tetrahedral 4 0.2 - 0.4 trigonal planar 3 0.1 - 0.2 linear 2 <0.15 = Radius of smaller ion Radius of larger ion r + /r- 3 A A C A A A A A A A A A A C Similar sizes, We can ft more oF anions around the cation Large size diFFerence We can ft less anions around the cation Common Structure of Ionic Solids A structure-type is usually named after the first compound for which it was determined (discovered) Often the most prevalent minerals...
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Inorganic Lecture 6 - 1 6th Lecture Today s Topics Ionic...

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