PPT: Atoms and Molecules | Science Class 9 PDF Download

 Page 1


Atoms & Atoms &
Molecules Molecules
Page 2


Atoms & Atoms &
Molecules Molecules
Laws of Laws of  Chemical Combination Chemical Combination
Given by Lavoisier and Joseph L. Proust as follows:
Law of Constant
Proportions
Law of Conservation
of Mass 
Mass can neither be
created nor destroyed in
a chemical reaction
A + B ? C + D
Reactants ? Products
Mass of reactants = Mass of products
Example:
In a chemical substance, the
elements are always present in
definite proportions by mass.
 In water, the ratio of the mass of
hydrogen to the mass of oxygen is
always 1:8 respectively.
Example:
Page 3


Atoms & Atoms &
Molecules Molecules
Laws of Laws of  Chemical Combination Chemical Combination
Given by Lavoisier and Joseph L. Proust as follows:
Law of Constant
Proportions
Law of Conservation
of Mass 
Mass can neither be
created nor destroyed in
a chemical reaction
A + B ? C + D
Reactants ? Products
Mass of reactants = Mass of products
Example:
In a chemical substance, the
elements are always present in
definite proportions by mass.
 In water, the ratio of the mass of
hydrogen to the mass of oxygen is
always 1:8 respectively.
Example:
Dalton’s Dalton’s  Atomic Theory Atomic Theory
Every matter is made up of very small or tiny particles called atoms.
Atoms are not divisible and cannot be created or destroyed in a chemical
reaction.
All atoms of a given element are the same in size, mass and chemical
properties.
Atoms of different elements are different in size, mass and chemical
properties.
Atoms combine in the ratio of small whole numbers to form compounds.
The relative number and kinds of atoms are constant in a given compound.
Atoms are the smallest particles of an element that can take part in a
chemical reaction.
Page 4


Atoms & Atoms &
Molecules Molecules
Laws of Laws of  Chemical Combination Chemical Combination
Given by Lavoisier and Joseph L. Proust as follows:
Law of Constant
Proportions
Law of Conservation
of Mass 
Mass can neither be
created nor destroyed in
a chemical reaction
A + B ? C + D
Reactants ? Products
Mass of reactants = Mass of products
Example:
In a chemical substance, the
elements are always present in
definite proportions by mass.
 In water, the ratio of the mass of
hydrogen to the mass of oxygen is
always 1:8 respectively.
Example:
Dalton’s Dalton’s  Atomic Theory Atomic Theory
Every matter is made up of very small or tiny particles called atoms.
Atoms are not divisible and cannot be created or destroyed in a chemical
reaction.
All atoms of a given element are the same in size, mass and chemical
properties.
Atoms of different elements are different in size, mass and chemical
properties.
Atoms combine in the ratio of small whole numbers to form compounds.
The relative number and kinds of atoms are constant in a given compound.
Atoms are the smallest particles of an element that can take part in a
chemical reaction.
Size of Size of  an Atom an Atom
Atomic radius is Atomic radius is
measured in nanometres. measured in nanometres.
Atomic radii of hydrogen
atom = 1 × 10 m.
-10
Page 5


Atoms & Atoms &
Molecules Molecules
Laws of Laws of  Chemical Combination Chemical Combination
Given by Lavoisier and Joseph L. Proust as follows:
Law of Constant
Proportions
Law of Conservation
of Mass 
Mass can neither be
created nor destroyed in
a chemical reaction
A + B ? C + D
Reactants ? Products
Mass of reactants = Mass of products
Example:
In a chemical substance, the
elements are always present in
definite proportions by mass.
 In water, the ratio of the mass of
hydrogen to the mass of oxygen is
always 1:8 respectively.
Example:
Dalton’s Dalton’s  Atomic Theory Atomic Theory
Every matter is made up of very small or tiny particles called atoms.
Atoms are not divisible and cannot be created or destroyed in a chemical
reaction.
All atoms of a given element are the same in size, mass and chemical
properties.
Atoms of different elements are different in size, mass and chemical
properties.
Atoms combine in the ratio of small whole numbers to form compounds.
The relative number and kinds of atoms are constant in a given compound.
Atoms are the smallest particles of an element that can take part in a
chemical reaction.
Size of Size of  an Atom an Atom
Atomic radius is Atomic radius is
measured in nanometres. measured in nanometres.
Atomic radii of hydrogen
atom = 1 × 10 m.
-10
John Dalton
Symbols of Symbols of  Atoms Atoms
Symbols for some elements as proposed by Dalton: Symbols for some elements as proposed by Dalton: