Carbon-carbon double bonds (unsaturations) are found in naturally occurring fatty acids. There may be one double bond or many, up to six in important fatty acids. Fatty acids with one double bond are the most prevalent in the human body, comprising about half of the total.
The double bond of an alkene consists of a sigma (σ) bond and a pi (π) bond. Because the carbon-carbon π bond is relatively weak, it is quite reactive and can be easily broken and reagents can be added to carbon.
There is no 4 bond formed between carbon because of the carbon electron orbitals. Since it has 4 valence electrons, it needs 4 more to electrons to fill its outer energy level. It does so by forming covalent bonds with another element, in order to complete its Octet rule.
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