NCERT Class 9 Science

NCERT Class 9 Science Solution, Notes, Atoms and molecules

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Atoms and molecules 1.        Laws of chemical combination Law of conservation of mass: Mass can neither be created nor destroyed in a chemical reaction Law of constant proportion or Law of definite proportion:  In a chemical substance the elements are always present in definite proportions by mass 2.        Postulates of Dalton’s atomic theory All matter … Read more

NCERT Class 9 Science Lesson Structure of atom Solution and Notes

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Structure of atom Ionisation of gases in the discharge tube proved that atoms have subatomic particles Summary of characteristics of electrons, protons and neutrons Particle Electron Proton Neutron Symbol e p n Relative charge -1 +1 0 Nature Negatively charged Positively charged Neutral Discovered by JJ Thomson E. Goldstein Chadwick Thomson model of atom: An … Read more