Page 58 - Science Class 07

v We shall first write number the right hand So, the balanced equa on will be in the form as
side as 2MgO. shown below:

v Then, we shall mul ply Mg by 2 to make it 2Mg + O 2MgO
2
2Mg on the le hand side also.

1. What is the difference between monoatomic and diatomic element?
2. What does the atomicity of an element or compound tell us?

3. What do you mean by chemical formula?

4. What happens when electricity passes through water?
5. How many atoms of hydrogen and oxygen are present in the compound 2H O?
2

When water vapour combines with smoke (containing CO ) carbonic acid is formed. This
2
makes the rain water acidic. This results the acid rain that causes harm to monuments
and plants.

Matter : Anything that occupies space and has mass or weight
Element : The simplest form of a pure substance

Metals : Elements which are malleable, ductile and good conductor of electricity
Non-metals : Elements which are brittle and cannot be beaten into sheets
Metalloids : Elements that possess the characterstics of both metal and non-metals

Atom : The smallest particle of an element
Compound : Pure substance made up of two or more elements
Molecule : The smallest particle of a compound

Mixtures : Substances which contain two or more elements and these elements can
be separated
Chemical reaction : Combining two or more elements or compounds to form a new
compound
Chemical formula : Representation of elements or compounds according to the presence of
the atom in them

58 Science-7