Defining Cohesion
Cohesion is the intermolecular attractive force that exists between molecules of the *same* substance. It is essentially what makes a material 'stick to itself' or holds its constituent parts together.
The Underlying Forces
These attractive forces stem from various types of intermolecular bonds, such as hydrogen bonds, dipole-dipole interactions, or London dispersion forces. The strength of cohesion varies greatly depending on the specific substance and the nature of these intermolecular forces. For instance, water exhibits strong cohesive forces due to extensive hydrogen bonding between its molecules.
Practical Examples of Cohesion
A common illustration of cohesion is the formation of water droplets. The water molecules are strongly attracted to one another, causing them to pull inward and create a spherical shape. Another example is why a glass can be filled slightly above its rim without immediately spilling, as cohesive forces hold the liquid surface together.
Importance and Applications
Cohesion plays a critical role in numerous natural and industrial processes. In biology, it is essential for the transport of water from roots to leaves in plants, a process known as transpiration. In materials science, strong cohesive forces contribute significantly to a material's tensile strength and overall structural integrity.