Chemistry is, the branch of science concerned with the properties, composition and structure of substances and the changes they undergo when they combine or react under specified conditions. Chemistry can be divided into branches according to either the substances studies or the types of study conducted. The primary division of the first type is between inorganic and organic chemistry. Divisions of the second type are physical chemistry and analytical chemistry. The original distinction between organic and inorganic chemistry arose as chemists gradually realized that compounds of biological origin were quite different in their general properties from those of mineral origin.