Compounds have certain characteristics and usually have certain composition. Example: Water is a compound, which is liquid at room temperature and has a boiling point of100℃; The freezing point is 0℃, which consists of two elements: hydrogen and oxygen. H2O has 1 water molecule and consists of 2 hydrogen atoms and 1 oxygen atoms. (Water molecules are composed of hydrogen atoms and oxygen atoms) Example: Sodium chloride (NaCl) is a compound formed by the chemical action (neutralization reaction) of hydrochloric acid (HCl) and sodium hydroxide (NaOH). HCl (AQ)+NaOH (AQ) → NaCl (AQ)+H2O (L) compounds are mainly divided into organic compounds, inorganic compounds and polymer compounds [1], ionic compounds and * * * valence compounds. Organic compounds contain hydrocarbons (or hydrocarbons), such as methane (CH4), which can be divided into sugars, nucleic acids, lipids and protein. Inorganic compounds do not contain hydrocarbons, such as lead sulfate (II, PbSO4), which can be divided into compounds separated from acids, bases, salts and oxides, and generally contain metal elements, such as sodium oxide * * * valence compounds, such as water. Note: Some compounds, such as acetic acid (CH3COOH) and acetate, are also patents of organic compounds. Honestly, I don't understand either!