The traditional oil we use to lubricate our car engine is called mineral oil because it is derived from crude oil. Mineral oil consists of hydrocarbon molecules extracted from the distillation of crude oil. They are mainly alkanes in the range of C-15 to C- 40.
An alkane is a saturated hydrocarbon consisting of only carbon and hydrogen atoms. Also called paraffin, it has the general formula of CnH2n+2. The simplest alkane is methane, CH4, where the n=1.
Due to the chemical and physical properties of the hydrocarbon alkanes, they have limited resistance to oxidation and thermal breakdown at very high temperature.
Synthetic oil, on the other hand, consists of synthetic molecules. They are artificially made and specially designed to provide excellent lubrication and stability at very high and also at low temperature. Since these synthetic molecules do not deteriorate easily, they can last longer than mineral oil even at extreme conditions in an engine.
Synthetic oil is more expensive than mineral oil, nevertheless, it is a superior lubricant to keep your car healthy. With mineral oil, it is recommended you change the oil every 5000 to 10,000 miles. Whereas using synthetic oil, you may change the oil every 20,000 miles.
Finally, it is important to note regardless of the type of oil you use, you should change your engine oil based on the recommended interval because it gets contaminated with combustion by-products that accumulate at about the same rate regardless of oil type.