As per this theory

 

  • All Matter is made up of tiny particles called Atoms, which participate in chemical reactions
    (All types of substances whether compound or mixture are made up of atoms)

Dalton Atomic Theory (Matters) - Teachoo-01.jpg

  • These atoms are indivisible; they cannot be created or destroyed in a chemical reaction
    (They cannot be broken down further)

Dalton Atomic Theory (ndivisible Atom)-Teachoo-01.jpg

  • All atoms of one element have same mass and chemical properties
    (Example - Mass of an atom of oxygen and the chemical properties it displays will always be same, in any different compounds it is present in)

Dalton Atomic Theory (Same Mass) - Teachoo-01.jpg

  • Atoms of different elements have different masses and chemical properties
    (Example - Mass of an atom of oxygen will always be different from mass of one atom of Hydrogen)

Dalton Atomic Theory (Different Mass) - Teachoo-01-01.jpg

  • Atoms combine in ratio of whole number to form compounds

    (Example -2 Atoms of Hydrogen combine with 1 atom of Oxygen to form one molecule of water H 2 O. These 2 and 1 are always whole numbers and not fractions)

Dalton Atomic Theory (Different Elements) - Teachoo-01.jpg

  • In a compound, number and kinds of different elements are constant
    (Example -Water whether obtained from tap or sea will always have 2 atoms of Hydrogen and 1 atom of Oxygen, this ratio of 2:1 will not change)

Dalton Atomic Theory (Chemical Formulas) - Teachoo-01.jpg

Drawbacks of Atomic Theory

 

  • Dalton viewed atoms as indivisible hard spheres that cannot be broken down further.


Dalton Atomic Theory (ndivisible Atom)-Teachoo-01.jpg

But this was not correct. Further studies showed that Atoms are further composed of protons, neutrons and electrons.

Atoms can be broken down into Protons, Neutrons and Electrons - Teachoo-01.jpg

Drawbacks of Atomic Theory

  • Another finding we say in Dalton's theory was that all atoms of one element have same mass and chemical properties

Dalton Atomic Theory (Same Mass) - Teachoo-.jpg

But this was proved to be wrong when isotopes were discovered. Discovery of isotopes proved that atoms of one element can have different masses also.
These are known as Isotopes.

ISOTOPES (Different Mass) -Teachoo-01.jpg

Drawbacks of Atomic Theory

  • Dalton’s theory also suggested that Atoms of different elements have different masses.

Dalton Atomic Theory (Different Mass) - Teachoo-01-01.jpg

  • However, 2 different elements can also have the same mass.
    These are known as Isobars.

2 diffrent elements can also have the same mass-ISOBARS-Teachoo-01.jpg

Drawbacks of Atomic Theory

Example -

In text Question -Page 33 Q3, Q4

NCERT Question -

 

 

 

  1. Class 9
  2. Chapter 3 Class 9 - Atoms And Molecules (Term 2)

About the Author

CA Maninder Singh's photo - Founder at Teachoo
CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo