Khondaker Afrina Hoque presented on isomorphism, beginning with its discovery and definition. Isomorphism refers to substances that are similar in crystalline form and chemical properties, represented by similar formulas. Examples of isomorphic substances include Cu and Ag with cubic structure, and ZnSO4, NiSO4, and BaSO4 which are orthorhombic. For substances to be isomorphic, they must have analogous chemical formulas, similarly sized ions, similar polarization of ions, and the same number and arrangement of positive and negative ions in similar unit cells. The law of isomorphism states that isomorphic crystals have similar constituents with the same total number and arrangement of atoms in the crystal lattice. This law was used historically to

1. PRESENTED BY:
Khondaker Afrina Hoque
Id: 1114015, Reg: 900048
Department of chemistry
Comilla university
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2. PRESENTATION ON
ISOMORPHISM
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3. Isomorphism
Discovery: E.Mistcherlish, 1819 (KH2PO4.H2O and KH2AsO4H2O)
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.
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4. ZnSO4 , NiSO4, BaSO4 - Orthorhombic
Fig: Orthorhombic structure
Other examples:
NaNO3, KNO3, CaCO3- rhombohedra
K2SO4, K2CrO4- Orthorhombic
NO3-, CO3
2- - Trigonal planar.
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5. Conditions of isomorphism:
For two substances to be isomorphous, the following conditions
must be satisfied.
(i) 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 .
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6.  In case of non-polar organic compounds, the following conditions
must be fulfilled before they can make isomorphs:
(i) Their chemical constitution must be analogous.
(ii) their crystal structures must be similar.
(iii) their molecular volumes must be very nearly equal.
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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”
1. Determination of atomic weight:
K2CrO4 is isomrphous with K2SO4 & and is found to contain 26.78% of
Cr.
& Atomic weight is 52.
Application of the law of isomorphism
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8. 1831 Berzelius-Atomic weight of vanadium is 61
and hexavalent
1868 Roscoe – pentavalent
3Pb3(VO4)2.PbCl2 is isomorphous with
Fluoroapatite , 3Ca3(PO4)2.CaF2
pyromorphite , 3Pb3(PO4)2.PbCl2
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.
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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: Ag2S and PbS.
Do not have same crystalline forms but still isomorphous.
example: FeSO4.7H2O (Green vitriol)
ZnSO4.7H2O (white vitriol).
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10. 12/14/2018 10
Thanks to all