Page 50 - Science Class 07
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Chemical Changes
• Ma er • Elements • Metals
• Non-metals • Metalloids • Atoms
• Compounds and Molecules • Elements and Molecules • Mixture s
• Chemical Compounds • Chemical Reac ons • Chemical Equa ons
• How to Balance an Equa on?
A large number of substances are found around This classifica on is based on the internal
us. Each substance has its own unique composi on of that ma er. Using composi on
proper es. However, we can group them into to describe ma er is be er than using its state,
solid, liquid and gas. Have you ever thought because the internal makeup makes ma er
why iron is solid while alcohol is liquid? Why unique and not its phase or state.
gases spread all around in the room while solid For example, water (symbol for water) can be
can not? This is because of the structural vapour, solid or the usual liquid. This means
difference of solid, liquid and gas. In this that scien fically, it is not correct to say water
chapter, you will study about basic structure of is a liquid, even though we all know that water
ma er and how do various things react with is usually a liquid.
each other and form a new substance.
In a similar vein, classifying ma er only
MATTER according to its colour, size or weight is not
Ma er is anything, such as a solid, liquid or enough because two iden cal objects can be of
gas, that has weight (mass) and occupies space. the same colour, but their internal makeup may
For anything to occupy space, it must have be different.
volume. Thinking about it, everything on the For example, a glass of water from a lake may
earth has weight and takes up space and that look and weigh the same as another iden cal
means everything on the earth is ma er.
glass of water from another lake, but it does
Classifica on of Ma er not mean they are the same. They are all water,
Ma er can be classified into two categories: but the chemical composi ons may be very
v Pure substances v Mixtures different.
50 Science-7
