NCERT Class 9 Science Solution, Notes, Atoms and molecules

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

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