In the most simple terms organic chemistry is the study of carbon based compounds while inorganic chemistry is the study of everything else. The reason we treat carbon based chemistry separately is because the carbon atom provides the backbone for almost all compounds found in living things. There are very specific rules for the way carbon bonds with other atoms and we can understand most of the chemistry based on these few rules. Inorganic chemistry mostly deals with metals which have somewhat different rules regarding bonding. The reason for these differences on the atomic level has to do with the arrangement of the electrons. Carbon has four valence electrons (electrons in its outermost shell) which means it typically forms four bonds. Inorganic atoms have different numbers of valence electrons (depending on its position in the periodic table/atomic number) and the electrons are found in different shells. These electrons bond differently than they do in carbon.

Organic chemistry is the study of compounds made of carbon,particularly hydrocarbons (molecules made up of carbon and hydrogen atoms). Compounds studied in organic chemistry can also have nitrogen,oxygen, sulfur, phosphorus, silicon, chlorine, fluorine, and other halogens.Inorganic chemistry deals with basically all of the other elements.Sometimes when a compound has both organic and inorganic parts, it is classified as organometallic. A common example of this is a transition metal with organic ligands.Although most biological molecules are purely organic, organometallic compounds play an important part in biochemistry and biological processes. For instance, hemoglobin in your blood is mostly organic,but it also contains iron so it does not fall strictly into the definition of organic chemistry.