A lipid is a substance that is soluble in organic solvents but usually not soluble in water. Lipids play a number of essential roles within biology and in particular are an essential component of cell membranes. Lipids are mainly composed of just four types of atoms: carbon, hydrogen, oxygen and nitrogen.


Carbon is the most biologically important atom, since it forms the backbone of organic molecules such as lipids. Carbon atoms contain six positively charged protons and six neutral neutrons within the nucleus. Six negatively charged electrons surround the nucleus. The outer electron shell in carbon has the potential to store four additional electrons. This crucial detail enables carbon to bond to up to four other atoms and form complex organic compounds. Lauric acid is an example of a simple lipid, which contains 12 carbon atoms.


Hydrogen is the simplest atom in the periodic table and is the most abundant element in the universe. Hydrogen consists of one positively charged proton and one negatively charged electron. In order to fill its outer shell, hydrogen covalently bonds with a number of elements, including carbon. This allows it to be a constituent of lipids. Lauric acid contains 24 hydrogen atoms.


Oxygen is the third-most abundant element in the universe and is essential to life on Earth. Oxygen atoms consist of eight electrons, eight neutrons and eight electrons. The outer electron shell of oxygen can potentially store an additional two electrons, allowing it to combine with up to two other atoms. The most well-known type of oxygen molecule, diatomic oxygen, consists of two oxygen atoms. The two potential bonds allows oxygen to combine with other biologically important elements and form lipids. Lauric acid contains two oxygen atoms.


Nitrogen atoms are not essential to lipids but can be found in select lipid structures. An example of a lipid chemical that contains nitrogen is hexadecyltrimethylammonium chloride. Nitrogen is the most abundant element within the Earth's atmosphere and is a major constituent in biological molecules. Nitrogen atoms contain seven protons, seven neutrons and seven electrons. The outer electron shell of nitrogen can harbor an additional three electrons. These electron shell vacancies can be used to covalently bond with other elements. The simple lipid, lauric acid, contains zero nitrogen atoms.