Nature of matter

Anything which has mass and occupies space is called matter.
Everything around us, for example, book, pen, pencil, water, air, all living
beings etc are composed of matter. Matters can be exists in three physical
states. They are Solid, Liquid, and Gas.

(i)    Solid have definite volume and definite shape

(ii)  Liquids have definite volume but they don’t have
a definite shape. They take the shape of the container in which they are placed

(iii)  Gases have neither definite volume nor definite
shape. They completely occupies the shape of the container in which they are
placed

These three states of matter can be interconvertible by changing the
conditions of temperature and pressure.

On heating solid usually changes to liquid and the liquid on further
heating changes to gaseous stage or vapor. In the reverse process a gas can be liquefied
by cooling it and liquid on further cooling freezes to the liquid stage.

Matters can be classified as mixtures and pure substances. Mixtures can be both
homogeneous as well as heterogeneous. Milk, air are examples of homogeneous
mixtures. They are uniform throughout. If they are not having uniform
composition, they are heterogeneous mixture. Iron and sand is an example of
heterogeneous mixtures. Elements like Cu, Ag and compounds like Nacl, AgNO₃ constitute
pure substance. Elements consist of only one type of particle. When   two or
more elements combine, they form compounds. The smallest particle of a compound
is a MOLECULE. Thus, copper is an element composed of Cu atoms whereas sodium
chloride is a compound composed of Na⁺Cl⁻ molecule.

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