Cohesion (chemistry)
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Repulsion (chemistry)
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intrinsic property of a substance that is caused by the shape and structure of its molecules, which makes the distribution of surrounding electrons irregular when molecules get close to one another, creating electrical attraction that can maintain a macroscopic structure such as a water drop. Cohesion allows for surface tension
, creating a "solid-like" state upon which light-weight or low-density materials can be placed.
van der Waals forces that operate by induced polarity
in non-polar molecules.
Cohesion, along with adhesion (attraction between unlike molecules), helps explain phenomena such as meniscus, surface tension and capillary action.
Mercury in a glass flask is a good example of the effects of the ratio between cohesive and adhesive forces. Because of its high cohesion and low adhesion to the glass, mercury does not spread out to cover the bottom of the flask, and if enough is placed in the flask to cover the bottom, it exhibits a strongly convex meniscus, whereas the meniscus of water is concave. Mercury will not wet the glass, unlike water and many other liquids,[2] and if the glass is tipped, it will 'roll' around inside.
See also
- Adhesion – the attraction of molecules or compounds for other molecules of a different kind
- Specific heat capacity – the amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius
- Heat of vaporization– the amount of energy needed to change one gram of a liquid substance to a gas at constant temperature
- amino acids
- Chemical polarity – a neutral, or uncharged molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end
References
- ^ Neil Campbell, Biology, 9th edition, p.92
- ^ Common science by Carleton Wolsey Washburne
External links
Wikimedia Commons has media related to Cohesion.
- The Bubble Wall[dead link] (audio slideshow from the National High Magnetic Field Laboratory explaining cohesion, surface tension and hydrogen bonds)
- "Adhesion and Cohesion of Water" – US Geological Survey
