What is the Difference Between Allotrope and Isomer

Elements display different characteristics due to their varying structural arrangements. Allotropes and isomers are two concepts in chemistry that demonstrate differences in structure and properties. This article examines the similarities and differences between allotropes and isomers, providing a brief overview of each.

What is the difference between allotrope and isomer? Allotropes are different structural forms of the same element, while isomers are different molecules with the same molecular formula.

Key Areas Covered

1. What is an Allotrope  
      – Definition, Features 
2. What is an Isomer 
      – Definition, Features 
3. Similarities Between Allotrope and Isomer
      – Outline of Common Features
4. Difference Between Allotrope and Isomer
      – Comparison of Key Differences
5. FAQ: Allotrope and Isomer
      – Frequently Asked Questions

Key Terms

Allotrope, Isomer

Difference Between Allotrope and Isomer - Comparison Summary

What is an Allotrope

Allotropes are different structural forms of the same element, characterized by distinct arrangements of atoms. In simpler terms, they represent various ways in which atoms can be bonded to form a particular element, leading to diverse physical and chemical properties.

Carbon provides a quintessential example of allotropes. Graphite, diamond, and fullerenes are all allotropes of carbon, each with unique structures and properties. Diamond consists of a three-dimensional crystal lattice, offering exceptional hardness, while graphite features layers of hexagonal structures, providing lubricating properties due to its slippery nature. Fullerenes, on the other hand, exhibit a spherical or tubular arrangement, showcasing distinctive conductive and structural qualities.


The existence of allotropes highlights the versatility of elements and their ability to exhibit diverse behaviors under different conditions. For instance, oxygen can manifest as diatomic oxygen (O2) in the atmosphere or as ozone (O3) in the stratosphere, showcasing allotropy. Similarly, phosphorus exists in various allotropes, such as white phosphorus, red phosphorus, and black phosphorus, each with its own set of characteristics.

What is an Isomer

Isomers are compounds that share the same molecular formula but possess different arrangements of atoms, resulting in distinct chemical structures and properties. This phenomenon arises from the diverse spatial orientations or bonding patterns of the constituent atoms within the molecules. The existence of isomers highlights the complexity and versatility of organic compounds.


Structural isomers, the most common type, differ in the arrangement of atoms and the connectivity of bonds. For example, both butane and isobutane have the molecular formula C4H10 but exhibit different structures, leading to contrasting physical and chemical properties. Stereoisomers, on the other hand, maintain the same connectivity but vary in the spatial arrangement of atoms. This category includes cis-trans isomers and enantiomers.

Cis-trans isomers, or geometric isomers, result from restricted rotation around a double bond. In cis isomers, similar groups are on the same side of the molecule, while in trans isomers, they are on opposite sides. Enantiomers, a subtype of stereoisomers, are mirror images of each other, like left and right hands. Despite having identical chemical formulas, enantiomers can display different biological activities, such as enzymes or receptors, due to their interactions with chiral environments.

Similarities Between Allotrope and Isomer

  1. Both allotropes and isomers involve variations in the arrangement of atoms, leading to different properties and structures.
  2. In both cases, the chemical composition remains unchanged.

Difference Between Allotrope and Isomer


  • Allotropes are different structural forms of the same element in the same physical state, while isomers are different compounds with the same molecular formula but different structural arrangements.


  • Allotropes exist within the same substance but in different forms under certain conditions, while isomers represent different chemical compounds that can coexist independently.


  • Examples of allotropes include different forms of carbon like graphite, diamond, and graphene, while examples of isomers include structural isomers like butane and isobutane, which have the same molecular formula but different structures.

FAQ: Allotrope and Isomer

1. Are diamond and graphite isomers or allotropes?

  • Carbon has many different allotropes. Graphite and diamond are two allotropes of carbon. They are both composed entirely of carbon atoms, but they have distinct structures and properties.

2. Which element has the most number of allotropes?

  • Carbon has the most number of allotropes. Some well-known carbon allotropes include diamond, graphite, and amorphous carbon. Other lesser-known allotropes of carbon include fullerene, carbon nanotubes, and graphene.

3. Does hydrogen have any allotropes?

  • Yes. Hydrogen has two allotropes as atomic and diatomic hydrogen. Atomic hydrogen consists of individual hydrogen atoms, while diatomic hydrogen consists of pairs of hydrogen atoms bonded together.

4. What is an example of an isomer?

  • Ethyl alcohol and dimethyl ether are isomers of each other as both compounds have the same molecular formula – C2H6O but different structural formulae.

5. Is graphite 100% carbon?

  • Yes. It is 100% pure carbon. Graphite is indeed one of the two naturally occurring forms of pure carbon, the other being diamond. Graphite consists entirely of carbon atoms arranged in a hexagonal lattice structure.


Allotropes demonstrate how elements can take on different forms, as seen in carbon’s graphite and diamond. Isomers, meanwhile, reveal the diversity possible within organic compounds, such as butane and isobutane. Although both involve changes in atomic arrangements, allotropes are variations in the structure of the same element, while isomers are entirely different compounds sharing the same molecular formulas. This difference between allotrope and isomer highlights the ability of elements and molecules to generate a wide range of distinct structures and properties.


1. “Allotropy.” Encyclopedia Britannica.
2. “Isomerism” Encyclopedia Britannica.

Image Courtesy:

1. “Diamond and graphite” By User:Itub – Self-made derivative work (see below) (CC BY-SA 3.0) via Commons Wikimedia
2. “Isomerism” By Vladsinger – Own work (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Hasini A

Hasini is a graduate of Applied Science with a strong background in forestry, environmental science, chemistry, and management science. She is an amateur photographer with a keen interest in exploring the wonders of nature and science.

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