Completar frases U.13: Complete the summaryVersión en línea Complete the summary of unit 13 por Rubén Campos 1 matter atoms Matter substances mass Elements volume matter mixture compound density measured pure International heterogeneous homogeneous System concentrated molecules Every object in the Universe is made by . has and takes up and it is formed by small particles called . Depending on which atoms constitue the substance , it has physical properties such as density , length and mass that can be and the result given in the units of the . The ratio between the mass and the volume of an object is called and it gives the idea of how is in a given volume of the substance . Atoms can join to form . are those substances formed only by one type of atom whereas a is a substance formed by molecules . Both elements and compunds are because they are formed by a single type of particles . When two or more pure substances are mixed , they form a , which can be ( if we can't distinguish the components ) or ( if we can identify the different components ) .