physical science ,standard vlll

2. BAISIC CONSTITUENTS OF
MATTER

3. ELEMENTS AND COMPOUNDS
 Elements are the pure substance which cannaot be
split into simple components through chemical
process.
 Compounds are the substance formed by the
combination of two or more elements through
chemical reactions

4. Origin of name of elements
Elements The basis of naming
Polonium Polond –country
Curium Marie Curie - scientist
Chromium Chrome – colour
Indium Indigo – colour
Neptunium Neptune – planet
Europium Europe - continent

5. Symbols are used for representing elements.symbols are
assigned to elements in different way.
The first letter of english name is used as the symbol for
elements in the table.The capital letters are used as the symbol.
Elements Symbols
Carbon C
Oxygen O
Nitrogen N
Hydrogen H
Sulphur S

6. Elements Symbols
Carbon C
Oxygen O
Nitrogen N
Hydrogen H
Sulphur S

7. Elements Symbols
Carbon C
Oxygen O
Nitrogen N
Hydrogen H
Sulphur S

8. Periodic table

9. Atoms and molecules
 Atoms is the smallest particle which shows all the
charecteristic propertis of an element
 Molecules are the smallest particles which can exist
independently

10. Method of representing Atoms and
Molecules
 Molecules with only one atom are called mono atomic
molecules.those with two atoms each are called
diatomic and molecules with more than two atoms are
called polyatomic molecules
Monoatomic Diatomic Polyatomic
Helium –He Hydrogen-H2 Phosphorous-P4
Neon-Ne Chlorin-Cl2 Sulphur-S8

11. Chemical formula
Molecules Atoms present Chemical formula
Carbondioxide Carbon-1,oxygen-2 CO2
Water Hydrogen-2,oxygen-1 H2O
Hydrogen chloride Hydrogen-1,chlorin-1 HCl
Sugar Carbon-12,hydrogen-
22,oxygen-11
C12H22O11
Sodium chloride Sodium-1,chloride-1 NaCl
Methane Carbon-4,hydrogen-4 CH4
H2O
CH4

12. Chemical Equation
 The substance taking part in a chemical reaction are
called the reactants.Substance formed as a result of the
reaction are called products
 C + O2 CO2
 H2+Cl2 2HCl
 Zn+2HCl ZnCl2 + H2

13. Balanced chemical equation
when a chemical equation is written,the number of
atoms of same kind,on the side of reactant and that of
product should be equal.this type of chemical equations
are called balanced chemical equations.
Zn + 2HCl ZnCl2 + H2
Atoms No: of atoms in
reactants
No:of atoms in
products
Zn 1 1
H 2 2
Cl 2 2