awnings Rules Pauling s Rules for lonic Crystals for lonic Crystals 2nd Rule- the electrostatic valence principle 3rd rule The sharing of edges, and particularly of faces, of adjacent poly hedra tend to decrease the stability of an ionic structure dn ISio l, strengths of Si-O=1, Strength=2, stable df l Al replace 1 Si, sTrength= 1+3/4=1.75, unstable af2 Al replace 2 Si, sTrength =3/4+3/4=1.5 very unstable 争争 Polyhedral Linking Paulings Rules 4th Rule: 器樂郎 An a crystal with different cations, those of high valence and small CN tend not to share polyhedral elements 是 n extension of rule3 The stability of structures with different types of lyhedral linking is vertex sharing edgesharing> ice.sharin Eeffect is largest for cations with high charge and low coordination number Especially large when r, /r approaches the lower Sit in Iv coordination is very unlikely to share limit of the polyhedral stabilit edges or faces Paulings rules Polarization of lon for lonic crystals Polarization of an ion is the distortion of the ctron cloud of the anion due to the influence of 5th Rule- Rule of Parsimony the nearby cation. .The number of different kinds of constituents in Perfect model of ionic compound a crystal tends to be small Not a purely ionic compound wards the cation and result in higher stronger bond is resulted8 In [SiO4 ], strengths of Si-O=1, åStrength=2,stable If 1 Al replace 1 Si, åStrength = 1+3/4=1.75, unstable If 2 Al replace 2 Si, åStrength =3/4+3/4=1.5 very unstable Pauling’s Rules for Ionic Crystals •2nd Rule ¾ the electrostatic valence principle 3rd Rule: The sharing of edges, and particularly of faces, of adjacent polyhedra tend to decrease the stability of an ionic structure Pauling’s Rules for Ionic Crystals Polyhedral Linking The stability of structures with different types of polyhedral linking is vertex-sharing > edge-sharing > face-sharing effect is largest for cations with high charge and low coordination number especially large when r+ /r- approaches the lower limit of the polyhedral stability 4th Rule: In a crystal with different cations, those of high valence and small CN tend not to share polyhedral elements An extension of Rule 3 Si4+ in IV coordination is very unlikely to share edges or faces Pauling’s Rules for Ionic Crystals 5th Rule ¾ Rule of Parsimony The number of different kinds of constituents in a crystal tends to be small Pauling’s Rules for Ionic Crystals Polarization of Ion Polarization of an ion is the distortion of the electron cloud of the anion due to the influence of the nearby cation. + – + – Perfect model of ionic compound Electron cloud of anion is attracted towards the cation and result in higher electron density between the ion, stronger bond is resulted. Ionic compound with polarization of ion ¾¾ Not a purely ionic compound