Soap consists of a polar (anionic), hydrophilic head and a non-polar hydrophobic tail. Soaps are usually sodium or potassium salts of long chain fatty acids and are biodegradable hence have little negative impact on environment. On the other hand, there are 3 classes of synthetic detergents:
1) Anionic: negatively charged head, usually a sulfonate or sulfate ion and a non-polar hydrocarbon tail (note that the end of this tail has a benzene ring attached).
2) Cationic: positively charged head, usually ammonium compounds with hydrogen atoms replaced by alkyl groups and a non-polar hydrocarbon tail.
3) Non-ionic: no charged head but rather a non-polar hydrocarbon tail and a polar end with many oxygen atoms attached that allow it to form hydrogen bonds with water.
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