There are very few elements that make up organic compounds, besides carbon, there are also a few elements such as hydrogen, oxygen, sulfur, nitrogen, phosphorus, and halogens. But the number of organic compounds is extremely large, with over 10 million species so far. The number of newly synthesized or isolated and identified organic compounds collected and organized by the Medical Education Network is still increasing day by day. The total number of inorganic compounds composed of over 100 elements other than carbon is less than one tenth of that of organic compounds. There are numerous organic compounds, which is also one of the reasons why we study organic chemistry as an independent discipline.

Definition of organic compounds：
Narrowly defined, organic compounds are mainly composed of carbon and hydrogen elements, and are compounds that contain a certain amount of carbon, but do not include carbon oxides, sulfides, carbonic acid, carbonates, cyanides, thiocyanates, cyanates, carbides, carboranes, alkyl metals, carbonyl metals, organic ligand complexes of metals, and other substances.
Organic matter is the material basis for the production of life, and all living organisms contain organic compounds. Fats, amino acids, proteins, sugars, hemoglobin, chlorophyll, enzymes, hormones, etc. The metabolism and genetic phenomena within living organisms both involve the transformation of organic compounds. In addition, many substances closely related to human life, such as oil, natural gas, cotton, dyes, synthetic fibers, plastics, organic glass, natural and synthetic drugs, etc., are closely related to organic compounds.
Organic compounds are all carbon containing compounds, but carbon containing compounds are not necessarily organic compounds.
The simplest organic compound is methane (CH4), which is widely distributed in nature and is the main component of natural gas, biogas, coal mine tunnel gas, etc., commonly known as gas. It is also the hydrocarbon with the smallest carbon content (the largest hydrogen content), and can be used as a fuel and raw material for producing substances such as hydrogen (H2), carbon black (C), carbon monoxide (CO), acetylene (C2H2), hydrogen cyanide (HCN), and formaldehyde (HCHO).