Atoms and Molecules Class 9 PPT

 Page 1


Atoms and
Molecules
Page 2


Atoms and
Molecules
History of Atom
· Ancient Indian and Greek philosopher have wondered about unknown and 
unseen form of matter. Around 500 BC, An Indian Philosopher Maharishi 
Kanad postulated that if we go on  dividing matter (padarth) we shall get 
smaller and smaller particles. Ultimately, a stage will come across the smallest 
particles beyond which further division will not be possible.
· He named these particles Parmanu. Another philosopher Pakudha Katyayama, 
elaborated this doctrine and said that these particles exist in combined form.
· Around the same era, ancient Greek philosophers– Democritus and Leucippus 
suggestion the same and coined the term atom. They just postulated.
· Antoine L. Lavoisier laid the foundation of chemical science by establishing 
two important laws of Chemical combination.
Page 3


Atoms and
Molecules
History of Atom
· Ancient Indian and Greek philosopher have wondered about unknown and 
unseen form of matter. Around 500 BC, An Indian Philosopher Maharishi 
Kanad postulated that if we go on  dividing matter (padarth) we shall get 
smaller and smaller particles. Ultimately, a stage will come across the smallest 
particles beyond which further division will not be possible.
· He named these particles Parmanu. Another philosopher Pakudha Katyayama, 
elaborated this doctrine and said that these particles exist in combined form.
· Around the same era, ancient Greek philosophers– Democritus and Leucippus 
suggestion the same and coined the term atom. They just postulated.
· Antoine L. Lavoisier laid the foundation of chemical science by establishing 
two important laws of Chemical combination.
Laws of Chemical combination.
· There are two laws of chemical combinations given after 
much experimentations by ANTOINE L. LAVOISER and 
JOSEPH L. PROUST.
· Two laws are:
1. Law of conservation of masses
2. Law of constant proportion.
Page 4


Atoms and
Molecules
History of Atom
· Ancient Indian and Greek philosopher have wondered about unknown and 
unseen form of matter. Around 500 BC, An Indian Philosopher Maharishi 
Kanad postulated that if we go on  dividing matter (padarth) we shall get 
smaller and smaller particles. Ultimately, a stage will come across the smallest 
particles beyond which further division will not be possible.
· He named these particles Parmanu. Another philosopher Pakudha Katyayama, 
elaborated this doctrine and said that these particles exist in combined form.
· Around the same era, ancient Greek philosophers– Democritus and Leucippus 
suggestion the same and coined the term atom. They just postulated.
· Antoine L. Lavoisier laid the foundation of chemical science by establishing 
two important laws of Chemical combination.
Laws of Chemical combination.
· There are two laws of chemical combinations given after 
much experimentations by ANTOINE L. LAVOISER and 
JOSEPH L. PROUST.
· Two laws are:
1. Law of conservation of masses
2. Law of constant proportion.
Law of Conservation of Masses
· Law of conservation of masses states that masses can niether be created nor 
destroyed in a chemical reaction. 
We can verify by doing an activity:
· Take 1.25g of copper sulphate in an ignition tube an mark it as A.
· Take 1.43g of sodium carbonate in a conical flask and mark it as B.
· Make the arrangement as shown in adjoining figure.
· Measure the weight.
· Now tilt and swirl the flask
· Now measure.
Conclusion:
· The mass of the flask doesn’t change after chemical reaction.
Page 5


Atoms and
Molecules
History of Atom
· Ancient Indian and Greek philosopher have wondered about unknown and 
unseen form of matter. Around 500 BC, An Indian Philosopher Maharishi 
Kanad postulated that if we go on  dividing matter (padarth) we shall get 
smaller and smaller particles. Ultimately, a stage will come across the smallest 
particles beyond which further division will not be possible.
· He named these particles Parmanu. Another philosopher Pakudha Katyayama, 
elaborated this doctrine and said that these particles exist in combined form.
· Around the same era, ancient Greek philosophers– Democritus and Leucippus 
suggestion the same and coined the term atom. They just postulated.
· Antoine L. Lavoisier laid the foundation of chemical science by establishing 
two important laws of Chemical combination.
Laws of Chemical combination.
· There are two laws of chemical combinations given after 
much experimentations by ANTOINE L. LAVOISER and 
JOSEPH L. PROUST.
· Two laws are:
1. Law of conservation of masses
2. Law of constant proportion.
Law of Conservation of Masses
· Law of conservation of masses states that masses can niether be created nor 
destroyed in a chemical reaction. 
We can verify by doing an activity:
· Take 1.25g of copper sulphate in an ignition tube an mark it as A.
· Take 1.43g of sodium carbonate in a conical flask and mark it as B.
· Make the arrangement as shown in adjoining figure.
· Measure the weight.
· Now tilt and swirl the flask
· Now measure.
Conclusion:
· The mass of the flask doesn’t change after chemical reaction.
Law of constant proportion.
· Lavoisier, along other scientist noted that many compounds were composed of two 
or more elements and each each such compound had the same element in the 
same proportions, irrespective of where the compound is comes from.
· Like in compound water (H
2
O), the ratio of the masses of hydrogen and oxygen is 
always 1:8, whatever the source of water. Means if 9g of H
2
O decomposed, 1g of 
Hydrogen and 8g of oxygen are always obtained.
· Similarly, In Ammonia NH
4 
, Nitrogen and Hydrogen are always lresent in the 
ratio of 14:3 by mass.
· So, this law stated by Proust as “In a chemical substance the elements are always 
present in a definite proportion by mass”.