Atoms And Molecules Class 9 Notes Science

Atoms and Molecules Class 9 Notes CBSE Science Chapter 3

NCERT Based CBSE Class 9th Revision Notes for Class include physics, chemistry, and biology notes on Chapter 3 atoms and molecules themes from the textbook. 

Science Notes provide an overview of the main points of each concept and topic in the NCERT TextBooks Class 9th Science. This Chapter Notes includes topic/concepts wise explanations for all the topics provided in the book such as Define Molecule, Atoms and Molecules Definition, Laws of Chemical Combination, Dalton's Atomic Theory Atoms, Symbols for Elements, writing chemical formulas, molar concept, 

Well prepared CBSE Class 9th Chapter Wise Science Notes  will guidance students understand the topics ,concepts and themes covered in all the chapters of Ncert Text book of 9th 

Atoms and molecules

Idea of divisibility

Maharishi kanad - 

He postulated that if we keep - on dividing the matter we will get smaller and Smaller particles. Ultimately we will achieve the Smallest particles  which may not divide further.

Pakudha Katyayan- 

He postulated that there are? various forms of matter because the particles of matter exist together in Combinations. Democritus and Leucippus- They suggested that when we Keep on dividing the matter there comes a time when no more  of the can take place.they called these particles atoms (meaning indivisible). 

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Laws of chemical Combination :

1 Low of Conservation of mass - Mass can neither be Created nor destroyed in a chemical reaction.

 Law of Constant Proportion- Elements are always Present in definite proportions by mass in a chemical substance- For example: Hydrogen and oxygen are present in water in a ratio of 1:8. Thus, if 9g of water is decomposed, 19 of hydrogen and of oxygen are always obtained. 89

Dalton Atomic Theory: 

John Dalton & a theory propose af in which he said, all matter whether it is an element, Compound or a mixture consist of tiny invisible particles called "atoms?

Postulates of dalton atomic theory 

(1) The matter is made up of tiny particles called atoms that cannot be divided.

(2.) Atoms are never formed or destroyed during a chemical reaction. (3) Atoms of an element have some nature. They have same size, mass and character

(4.) Atoms of different elements exhibit variant nature They do not have same characteristics.

(5) Alem from compounds by combining in a ratio of whole numbers-

 (6) A Compound Contains constant number and Kinds of atoms. What is an Atom? Atoms are the building blocks of matter. just the backs are the building blocks of building.

What is the size of an atom? 

Atoms are extremely small. More than millions of atoms when stacked would make a layer as thick as sheet of paper. Atomic radius is measured in nanometres 3= 1 nm

1m = 10 nm

Symbols for Atoms 8

Here are some examples of the symbols that used to represent different atoms

The Symbols for representing an atom are generated from the flast two letters of the element name. The first letter is always in uppercase (capital) while the Second letter is written in Lowercase (Small)

for complex-hydrogen

Aluminium, Al not AL Cobalt Co net co

Now-a-days, IUPAC [International Union of Pre and Applied chemistry approves rames of elements.

 

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