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Physical Properties - Melting Point

Learning Objective: To study the impact of symmetry, carbon numbers, geometry, and polarity on the melting point of solids.

Skill Level - Intermediate

 

Prerequisites: 

 

Chapter: Physical Properties

Sub-topic: Melting Point 

 

Author's Note: We definitely have witnessed substances burn and boil throughout our lives without giving much thought to their molecular structure. However, as a chemistry student, finding a compound's melting point requires burning a small sample in a capillary attached to a thermometer on a Thiele tube and gradually heating the handle using a flame. You must have noticed how some solids melt almost immediately while others gradually melt across various temperatures, depending on their nature. 

In this section, we will cover the structural aspects of a molecule that affect a solid compound's melting point. We will study the role of symmetry, carbon numbers, geometry, and polarity on the melting point of solids in organic chemistry. Since, two compounds may look similar in their molecular formula but have totally different melting points based on their arrangements. Finding the melting point is usually the first step in investigating an unknown compound, its purity, and its nature.

Physical Properties - Melting Point

Solids have a definite mass, shape, and volume due to strong, attractive forces holding the particles (atoms, ions, or molecules) in place. This rigidity is broken on heating when the particles acquire enough heat energy to vibrate intensely. The strong vibrations can break the attractive intermolecular force and cause the particles to move apart. As the distance between the particles increases, the solid starts to melt and undergoes a phase change to a liquid state. 

 

 

Therefore, the melting point is a characteristic property of solids and represents the temperature at which the transition to the liquid state occurs. The melting point can be a sharp or gradual transition depending on whether the solid is crystalline or amorphous. 

 

Melting Point in crystalline solids

A crystalline solid has particles arranged in fixed positions, and this arrangement.....

Major types of crystalline solids are-....

 

Impact of symmetry, carbon numbers, geometry, and polarity on the melting point

 

Role of symmetry

Symmetry allows solid compounds to pack tightly, allowing fewer vacant spaces. Now, more molecules occupy the volume per unit cell,....

 

Role of Polarity

In the nonpolar molecules, the attractive interactions are mainly due to ....

 

Role of Carbon numbers

Tight packing of molecules also depends on the odd and even number of carbon atoms. The molecules with....

 

Role of Geometry

Molecules’ geometry also impacts the melting point. Molecules with steric crowding pack....

 

Melting point in amorphous solids

The amorphous solid has no fixed arrangement of atoms. The bond lengths and bond angles....

 

Subscribe to learn about factors affecting the melting point of solids.

 

Physical Properties
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Common Types of Reactions

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Drawing Organic Structures

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Functional Groups in Organic Chemistry

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Intermolecular Forces

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Physical Properties

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Fundamentals of Organic Reactions

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Reactive Intermediates

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Stereoisomerism

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