There are now 109 kinds of substances that make up all matter at and above the atomic level. The simplest molecules have only one kind of atom, e.g., helium molecules, which have one atom per molecule. No chemical reactions take place, and no chemical bonds are formed between molecules. The molecules in the mixture can be separated mechanically. Gasoline is an example of a liquid mixture.
Air is a natural mixture in the gaseous state.
The chief function of the periodic table is to serve as a fundamental framework for the systematic organization of chemistry. The CRC Handbook has an example of the Periodic Table of the Elements inside the cover. The naming conventions in organic chemistry are one of the major obstacles in finding information about organic compounds. Yet, these older names continue to be used in the literature and by working chemists. Inorganic chemists' work often overlaps that of organic chemists in their interest in organometallic compounds.