Have you ever thought about why a sugar cube dissolves in your coffee? Well, the answer lies in a force called “Cohesion”. It is an invisible force that is present in all matter and is responsible for the attraction between two molecules. Today, in this blog, we will define cohesive force and know about its types and importance along with the difference between Cohesive force and Adhesive force.
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What is Cohesive force?
If you imagine magnets sticking to each other, you are looking at the effect of Cohesive force. These magnets are intermolecular forces just like “hydrogen bonds, dipole-dipole interactions and London Dispersion Forces. They attract molecules of the same substance to each other and create a cohesive force that holds them together.
The force is like an invisible glue. The stronger this glue is the stronger the attraction between the balls and the more tightly they will pack together. This also explains why some substances like liquids have a definite shape while others like gases have no definite shape at all.
Also Read – All About Faraday’s Law
Types of Cohesive Forces
There are many types of Cohesive Forces that act between molecules. They are –
- Intermolecular Forces – These forces are weak interactions between molecules and arise from temporary fluctuations in the electron distribution. For example – Hydrogen Bonds.
- Metallic Bondings – When we talk about metals, the valence electrons are delocalized and are free to move throughout the metal lattice. This creates a strong electrostatic attraction between the positively charged metal ions and the negatively charged sea of electrons that holds them together.
- Covalent Bonding – This type of bonding takes place when there is a sharing of electrons between atoms. The shared electrons create a strong attraction between the atoms and hold the molecules together.
Also Read – Types of Motion: Definition & Examples I
Importance of Cohesive Force
These forces are important in our day-to-day phenomena as they are present everywhere. Thus, the importance of Cohesive force is –
- Transportation of Water in Plants – It is cohesion that allows for the flow of water to travel against gravity through the xylem of plants.
- Shape of Liquids – Cohesion force gives liquids their characteristic shape and allows them to form a shape.
- Boil and Melt Point – The strength of the Cohesive forces determines the temperature at which a substance boils or melts.
- Surface Tension – Cohesion contributes to surface tension which allows insects to walk on water and small objects to float.
What is the difference between Cohesive and Adhesive Force?
|When two same types of molecules attract each other an attraction force is created called a Cohesive Force
|When two different molecules attract each other and an attraction force is created is called an Adhesive Force
|A strong cohesive force in water leads to the formation of water droplets on the surface
|A strong adhesion force in water leads to its spreading over the surface.
|The cohesive force is oten caused by hydrogen bonding or Van der Waals forces.
|The adhesive force is caused by electrostatic or mechanical forces existing between two different molecules.
Examples of Cohesive Force
There are plenty of examples present in front of us that show us the existence of Cohesive force. Some of them are –
- Water Droplets – Cohesion allows water molecules to stick together and form round droplets and create surface tension.
- Oil on Water – Although oil molecules are attracted to each other due to cohesion, they are not attracted to water because of adhesion force. This is why oil forms a separate layer on top of water.
- Mercury Beads – The strong cohesive forces between mercury atoms make them form spherical beads on the surface.
- Solid Objects – The strong cohesive forces in solids hold the atoms and molecules tightly and packed together, giving them their rigid structure.
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