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Some Basic Concepts of Chemistry 5 Fig. 1.1 Arrangement of particles in solid, liquid Fig. 1.2   Classification of matter and gaseous state (iii) Gases have neither definite volume nor completely mix with each other. This means definite shape. They completely occupy particles of components of the mixture are the space in the container in which they uniformly distributed throughout the bulk of are placed. the mixture and its composition is uniform These three states of matter are throughout. Sugar solution and air are the examples of homogeneous mixtures. In interconvertible by changing the conditions contrast to this, in a heterogeneous mixture, of temperature and pressure. the composition is not uniform throughout Solid liquid Gas and sometimes different components are On heating, a solid usually changes to visible. For example, mixtures of salt and a liquid, and the liquid on further heating sugar, grains and pulses along with some dirt (often stone pieces), are heterogeneous changes to gas (or vapour). In the reverse process, a gas on cooling liquifies to the liquidixtures. You can think of many more and the liquid on further cooling freezes to examples of mixtures which you come across the solid. in the daily life. It is worthwhile to mention here that the components of a mixture can 1.2.2. Classification of Matter be separated by using physical methods, In Class IX (Chapter 2), you have learnt that such as simple hand-picking, filtration, at the macroscopic or bulk level, matter can crystallisation, distillation, etc. be classified as mixture or pure substance. These can be further sub-divided as shown Pure substances have characteristics different from mixtures. Constituent particles in Fig. 1.2. of pure substances have fixed composition. Copper, silver, gold, water and glucose are When all constituent particles of a substance are same in chemical nature, it some examples of pure substances. Glucose is said to be a pure substance. A mixture contains carbon, hydrogen and oxygen in contains many types of particles. a fixed ratio and its particles are of same composition. Hence, like all other pure A mixture contains particles of two or more pure substances which may be present substances, glucose has a fixed composition. in it in any ratio. Hence, their composition is Also, its constituents—carbon, hydrogen and oxygen—cannot be separated by simple variable. Pure substances forming mixture physical methods. are called its components. Many of the substances present around you are mixtures. Pure substances can further be classified For example, sugar solution in water, air, into elements and compounds. Particles tea, etc., are all mixtures. A mixture may of an element consist of only one type of be homogeneous or heterogeneous. In a atoms. These particles may exist as atoms or homogeneous mixture, the components molecules. You may be familiar with atoms Reprint 2026-27