Adhesion and cohesion are two simultaneously used terms, and both refer towards the attraction phenomena of molecules of an element or compound. These two terms are often confused and mixed up with each other as they refer to similar functionality, but in actual they are different in nature and occurrence. Adhesion refers to the attraction between different kinds of molecules. It is usually seen in the compounds where different molecules combine to form a whole new compound. On the other hand, Cohesion is the inter-molecular attraction force between like molecules, or we can say that attraction between similar molecules is referred as cohesion.
What is Adhesion?
Adhesion is the term that is used to for the inter-molecular attraction between unlike molecules. We can also say that adhesion is the phenomena of attraction between different kinds of molecules. It usually happens in the case of compounds. Whenever two different kinds of elements are mixed or reacted with each other, the resulting product after the chemical reaction or chemical combination is a chemical compound which possesses both kinds of molecules from the reacting elements. Different molecules are present in a mixture and compound. They possess their sort of attraction forces between them. The force of attraction between two different kinds of molecules in nature is usually termed as Adhesion. For example, water H2O is a compound that is formed by the combination of hydrogen and oxygen. Inside the water, hydrogen and oxygen molecules are kept bonded with each other by attractive forces; this is adhesion. The force of attraction between hydrogen and oxygen molecules. The basic force of attraction is responsible for initially chemical bonding, and then it makes way for the formation of new products or compounds. By forces of attraction and nature of combination, adhesion force is divided into various kinds that include, Dispersive adhesion, chemical adhesion, and diffusive adhesion. Chemical adhesion is usually the most widely found adhesion kind. It is usually present in the compounds formed due to ionic bonding, hydrogen bonding, and covalent bonding. Regarding Dispersive adhesion, the famous forces of attraction given the name against the scientist to discover them, Van der Waals forces are present between different kinds of molecules that participate in the formation of the compound. Whenever two different sorts of molecules combine with each other and both are mobile in nature and are quite soluble, then the adhesion is termed as diffusive adhesion.
What is Cohesion?
Cohesion is the term that depicts the force of attraction between like molecules. We can also say that cohesion is the phenomena that refer towards the attraction of similar kind of molecules with each other. It is unusually found in the elements. An atom is the basic functional unit of an existing thing. Molecules are the combination of atoms. In the elements the forces of attraction present between the same kind of molecules that keep that element in its particular shape and help in the determination of the state of the element. For example, the forces of attraction between the molecules of gases like oxygen and nitrogen are weak as compared to the forces of attraction between aluminum and iron. That’s why oxygen and nitrogen are easy to break down and thus are in gaseous form, whereas iron and aluminum are in solid form and are more difficult to break down. The word cohesion is derived from a Latin word coherent which means “to stay together or stick together.” It falls on the intrinsic property of an element and defines its shape and state. By the structure of molecules and their arrangement, it is more likely to judge the reactivity and nature of the whole substance. Even in the compounds, where the intermolecular forces are present in different kinds of molecules, the molecules of same nature still do possess the inter-molecular forces in between due to which they sustain as their own and depict their presence inside a compound. The most common example that clarifies both these phenomena is whenever Mercury is placed inside a glass, the cohesive forces between its own like molecules is way greater than the adhesive forces between the unlike molecules of mercury and glass, due to which mercury sustain its shape in the glass.
Adhesion vs. Cohesion
- Adhesion is an attraction between unlike molecules.
- Cohesion is an attraction between like molecules.
- Adhesion is only found in mixtures and compounds.
- Cohesion is present in elements and compounds both.
- Adhesion is responsible for the formation of new compounds.
- Cohesion defines the shape and state of an element.