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Allotropes Chemistry Tutorial

Key Concepts

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Allotropes of Oxygen

There are two main allotropes of oxygen:

Both allotropes of oxygen are made up only of oxygen atoms, but they differ in the arrangement of the oxygen atoms:

Molecular oxygen, O2, and ozone, O3, have different physical properties such as colour, odour, melting and boiling point, density and solubility.
Some properties of the allotropes of oxygen are shown in the table below:

  Allotropes of Oxygen
Property Molecular Oxygen (O2) Ozone (O3)
Structure O=O


Colour colourless gas
pale blue liquid
pale blue solid
pale blue gas
deep blue liquid
deep violet solid

Odour odourless sharp, pungent

Melting Point (°C) -219 -193

Boiling Point (°C) -183 -111

Density (20°C) 1.3 g L-1 2.0 g L-1

Solubility in Water slightly soluble more soluble that O2

Chemical Stability stable decomposes to O2 easily

Uses common oxidiser sterilising agent
(it is poisonous to many living things)

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Allotropes of Carbon

The two most common, naturally occurring allotropes of carbon:(1)

Both graphite and diamond are made up of carbon atoms, but the arrangement of atoms is different in each allotrope which results in different physical properties.
In particular, the presence of delocalised electrons in the structure of graphite results in it being soft and a good electrical conductor whereas diamond is very hard and an electrical insulator.

Some properties of graphite and diamond are shown in the table below:

  Allotropes of Carbon
Property Graphite Diamond
Each carbon atom is bonded to 3 other carbon atoms in layers with delocalised electrons between the layers.
Each carbon atom is bonded to 4 other carbon atoms in a 3-dimensional covalent network. All valence electrons are used in bonding.

Colour black colourless

Melting Point (K) sublimes at ≈3500 sublimes at ≈4000

Electrical Conductivity good
Delocalised electrons between the layers allow an electric current to pass through
poor (an insulator)
No delocalised electrons to allow for the flow of electrical current

Hardness (Mohs Scale) 1-2 (soft)
Delocalised electrons allow the sheets to move over each other
Hardest known natural mineral.

Chemical Stability stable decomposes slowly over time

Uses lubricant
because it is soft
because it is so hard

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Allotropes of Phosphorus

There are three allotropes of phosphorus:

Some properties of the allotropes of phosphorus are given in the table below:

Property White Phosphorus Red Phosphorus Black Phosphorus
Structure P4 molecules packed into a crystal Chains of P4 molecules
Puckered layers of phosphorus atoms

Colour white red black

Chemical Stability least

Allotropes of Sulfur

Sulfur has several allotropes:

Allotropes of Tin

There are three allotropes of tin:

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(1) This statement is probably not as "true" as it once was.
You might like to read about Graphene and Fullerenes, nanoscale allotropes of carbon.