Isomorphism

educational purpose

1. PRESENTED BY: Khondaker Afrina Hoque Id: 1114015, Reg: 900048 Department of chemistry Comilla university 11/23/2017 1

2. PRESENTATION ON ISOMORPHISM 11/23/2017 2

3. Isomorphism Discovery: E.Mistcherlish, 1819 (KH 2 PO 4 .H 2 O and KH 2 AsO 4 H 2 O ) Definition: substances are said to be isomorphous which are in similar in crystalline form and in chemical properties, can be represented by similar formulae. Isomorphism: iso = same + morphus = form Examples: Cu, Ag- cubic structure. Fig: cubic structure . 11/23/2017 3

4. ZnSO 4 , NiSO 4 , BaSO 4 - Orthorhombic Fig: Orthorhombic structure Other examples: NaNO 3 , KNO 3 , CaCO 3 - rhombohedra K 2 SO 4 , K 2 CrO 4 - Orthorhombic NO 3- , CO 3 2- - Trigonal planar. 11/23/2017 4

5. Conditions of isomorphism: For two substances to be isomorphous, the following conditions must be satisfied. Chemical formulae must be analogous, (ii) the size of the ions must not be very Different (iii) the polarization of the ions must not be very different , ( iv) the substances must have similar unit cells containing the same number of positive and negative ions in geometrically similar positions. (v) have the same chemical composition and arrangement of atoms or ions . 11/23/2017 5

6. In case of non-polar organic compounds , the following conditions must be fulfilled before they can make isomorphs: Their chemical constitution must be analogous. ( ii) their crystal structures must be similar. (iii) their molecular volumes must be very nearly equal. 11/23/2017 6

7. Law of isomorphism Mitscherlisch (1819) stated as follows: “Isomorphous crystals have similar constituents i.e they contain the same total number of atoms arranged in similar manner in the crystal lattice” Determination of atomic weight: K 2 CrO 4 is isomrphous with K 2 SO 4 & and is found to contain 26.78% of Cr . & Atomic weight is 52. Application of the law of isomorphism 11/23/2017 7

8. 1831 Berzelius-Atomic weight of vanadium is 61 and hexavalent 1868 Roscoe – pentavalent 3Pb 3 (VO 4 ) 2 .PbCl 2 is isomorphous with Fluoroapatite , 3Ca 3 (PO 4 ) 2 .CaF 2 pyromorphite , 3Pb 3 (PO 4 ) 2 .PbCl 2 Corrected atomic weight: 50.92. 2. Correction of atomic weight: 3 . Determination of valancy: Valancy of Be. Mandeleev - it resembles with Al & valancy is 3. Mallard – BeO resembles with ZnO & valancy is 2 not 3. 11/23/2017 8

9. Limitations of law of isomorphism: Same number of atoms, possess similar chemical formula yet are not isomorphous . Possess different structure and contain unequal number of atoms ,yet are isomorphous . example: Ag 2 S and PbS. Do not have same crystalline forms but still isomorphous. example : FeSO 4 .7H 2 O (Green vitriol) ZnSO 4 .7H 2 O (white vitriol ). 11/23/2017 9

10. 11/23/2017 10 Thanks to all