Difference Between Isomorphism and Polymorphism

Key Difference – IsomorphismvsPolymorphism

Compoundscan exist in different forms in nature. These different forms can be different morphologies or different structures. The structure of a chemical compound determines the physical properties of that compound. Sometimes the chemical properties are also determined by the structure. “Morphism” is a term used to name the term “morphology”. It describes the external appearance of a compound. The terms isomorphism and polymorphism are used to describe these external appearances. Polymorphism means the existence of a compound in more than onecrystallineform. Isomorphism is the existence of two or more compounds having the same morphology. Thekey differencebetween isomorphism and polymorphism is thatisomorphism refers to the presence of two or more compounds with identical morphologies whereas polymorphism refers to the presence of different morphologies of the same substance.

CONTENTS

1.Overview and Key Difference
2.What is Isomorphism
3.What is Polymorphism
4.并排比较,同构和变形ism in Tabular Form
5.Summary

What is Isomorphism?

Isomorphism refers to the presence of two or more compounds with identical morphologies. This means the existence of the same crystal structure in different compounds. These compounds are known as isomorphous substances. Isomorphous substances have nearly the same shape and structure.

These compounds have the same ratio between atoms present in those compounds. This indicates that theempirical formulasof isomorphous substances are identical. But the physical properties of the isomorphous substances are different from each other because they have different atomic combinations. Ex:mass, density, chemical reactivity are some of the physical properties that differ in isomorphous substances. Let us consider some examples in order to understand what isomorphism in chemistry is.

• Calcium carbonate (CaCO₃) and sodium nitrate (NaNO₃).

Both calcium carbonate and sodium nitrate are trigonal in shape. The atomic ratio of the atoms present in each compound is 1:1:3. But these compounds have different physical and chemical properties. Theirmolar massesare also different from each other (Calcium carbonate = 100g/mol and sodium nitrate = 85 g/mol).

• Sodium phosphate (Na₃PO₄) and sodium arsenate (Na₃AsO₄).

These compounds exist in tetrahedral shape, and the empirical formula of these compounds have the atomic ratio 3:1:4. But they have different chemical and physical properties.

What is Polymorphism?

Polymorphism refers to the presence of different morphologies of the same substance. The substance that shows polymorphism is known aspolymorphic substances. Here, a particular compound exists in different shapes and crystalline forms.

Polymorphic substance show similarities and differences based on the structure. But most of the time, the chemical properties are the same since it is the same compound that exists in different forms. But the physical properties are different. , CaCO3 (calcium carbonate) exist in either orthorhombic form or in hexagonal form.

Allotropy is a related term to the polymorphism. Allotropy refers to the polymorphism of a particular element. The compounds showing allotropy are known as allotropes.Allotropesoccur when an element forms a crystalline structure with different arrangements. For example carbon form allotropes such as diamond or graphite. These allotropes have different chemical and physical properties.

What is Difference Between Isomorphism and Polymorphism?

Isomorphism vs Polymorphism
Isomorphism refers to the presence of two or more compounds with identical morphologies.	Polymorphism refers to the presence of different morphologies of the same substance.
Shape
Isomorphous substances have identical shapes.	Polymorphic substances have different shapes.
Compound
Isomorphism concerns two or more different compounds.	多态性描述的不同形式same compound or element.
In Elements
Isomorphism is absent in elements.	Polymorphism is present in elements.
Atomic Ratio
Isomorphous substances have the same atomic ration in the empirical formula.	Polymorphic substances have either similar or different atomic ratios.

Summary –IsomorphismvsPolymorphism

Isomorphism and polymorphism express two opposite ideas. The difference between isomorphism and polymorphism is that isomorphism refers to the presence of two or more compounds with identical morphologies whereas polymorphism refers to the presence of different morphologies of the same substance.

Reference:

1.“Crystallization and Polymorphism.” American Chemical Society.Available here
2.“Isomorphism (Crystallography).” Wikipedia, Wikimedia Foundation, 17 Feb. 2018.Available here
3.“Allotropy.” Wikipedia, Wikimedia Foundation, 3 Mar. 2018.Available here

Image Courtesy:

1.’CaCO3-calcite-structure’By Tem5psu – Own work,(CC BY-SA 4.0)viaCommons Wikimedia(Modified)
2.’Sodium-nitrate-unit-cell-3D-balls’By Ben Mills – Own work, (Public Domain) viaCommons Wikimedia(Modified)
3.’Allotropes of Carbon’By Mstroeck (talk) (Uploads) – Own work,(CC BY-SA 3.0)viaCommons Wikimedia