Chemistry deals with the composition, structure and properties of matter. Anything that has mass and occupies space is called matter. Matter mainly exists in three forms - solid, liquid and gaseous states. These forms are interconvertible by changing temperature and pressure. The chapter touches upon topics such as the importance of chemistry, atomic mass, and molecular mass. Some basic laws and theories in chemistry such as Dalton’s atomic theory, Avogadro law, and the law of conservation of mass are also discussed in this chapter. Chemical properties are characteristic reactions of different substances; these include acidity or basicity, combustibility etc.