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The process of cooling a hot , concentrated

substance to obtain crystals is called

crystallisation. It·s the method used to purifysolids. Crystallisation is the process that

separates a pure solid in the form of its crystals

from a solution. For e.g. We can obtain a pure

copper sulphate from an impure sample by the

process of crystallization.

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There are several differences between a physical and

chemical change in matter or substances.

The properties which can be observed and specified like

colour ,hardness ,rigidity ,fluidity ,density ,melting

point ,boiling point etc.. are caller physical properties.

Chemical Properties are the properties used tocharacterize materials in reactions that change their

identity

A physical change in a substance doesn't change what

the substance is. In a chemical change where there is a

chemical reaction, a new substance is formed andenergy is either given off or absorbed.

For example, if a piece of paper is cut up into small

pieces it still is paper. This would be a physical change

in the shape and size of the paper. If the same piece of

paper is burned, it is broken up into different

substances that are not paper.

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Physical changes can be reversed, chemical changes cannot be

reversed with the substance changed back without

extraordinary means, if at all. For example, a cup of water canbe frozen when cooled and then can be returned to a liquid

form when heated.

If one decided to mix sugar into water to make sugar water, this

would be a physical change as the water could be left out to

evaporate and the sugar crystals would remain. However, if onemade a recipe for a cake with flour, water, sugar and other

ingredients and baked them together, it would take

extraordinary means to separate the various ingredients out to

their original form.

When heat is given off in a chemical change or reaction, it is

called an exothermic reaction. When heat is absorbed in achemical change or reaction, it is called an endothermic

reaction

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On the basis of chemical composition they can be classified either as

elements or compounds .

It the basic form of matter that cannot be broken down into simpler

substances by chemical reactions .Robert Boyle was the first scientistto use the term element in 1661.

Elements can be normally divided into metals ,non-metals and

metalloids

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1)Metals are lustrous, they shine.

2)They are having silver grey or golden yellow colour.

3)They conduct heat and electricity.

4)They are ductile ,can be drawn into wires,

5)They are malleable ,can be hammerer into thin sheets.6)They are sonorous , make a ringing sound when they are hit.

7)Some examples of metals are gold ,silver ,copper ,iron, etc« .

8)Metals are liquid at room temperature (Exept Mercury it·s the

only metal which is liquid even at the room temperature)

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1)They display a variety of colours.2)They are poor conductor of heat and

electricity.

3)They are not lustrous sonorous or malleable

.

4)Some examples of non-metals are iodine,oxygen ,etc«. .

Some elements which intermediate theproperties of metals and non-metals are

called metalloids.

Example of a metalloid is boron ,silicon

etc«. .

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1)Compound is a substance consisting of 2 or

more elements.

2)The simplest form of a compound is

a molecule.

3)Every molecule of a compound contains 2 of

more atoms.4)Example of a compound is Salt. Send an

electric charge through salt, and it breaks back

down into Chlorine and Sodium.

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