CBSE · Class 9 · Science · Chapter 8

Journey Inside the Atom

Journey inside the atom to examine subatomic particles, atomic models and the arrangement of electrons.

14 lessons 50 min
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Lessons in this chapter

  1. 1Rediscovering the Roots of Atomic TheoryFrom parmanu and atomos to Dalton, the atom changes from a philosophical idea into a scientific model
  2. 2A Short Historical Journey Through Atomic ModelsRadioactivity, cathode rays and Thomson's model reveal that atoms contain smaller particles
  3. 3Testing Thomson's Model: The Gold Foil ExperimentAlpha-particle scattering supplies the evidence that leads to a nuclear atom
  4. 4Rutherford's Model of an AtomA tiny nucleus explains the scattering evidence but creates a new problem of atomic stability
  5. 5Bohr's Model of the AtomAllowed energy levels address the stability problem and introduce shells and stationary states
  6. 6What Components Contribute to the Mass of an Atom?The neutron completes the basic particle picture and explains why proton count alone cannot account for mass
  7. 7Symbols of ElementsStandard element symbols make chemical communication compact and internationally consistent
  8. 8Atomic Number and Mass NumberAtomic number identifies an element while mass number counts its nuclear particles
  9. 9How Are Electrons Distributed in Different Energy Levels?Bohr and Bury rules build the electronic configurations of the first eighteen elements
  10. 10Combining Capacity of an Atom: ValencyValence electrons and stable outer shells explain common combining capacities
  11. 11A Deeper Look into Atomic Structure — IsotopesSame proton number with different neutron count produces isotopes of one element
  12. 12Average Atomic MassNatural isotope abundance determines weighted average atomic mass
  13. 13IsobarsDifferent elements can share the same mass number while having different atomic numbers
  14. 14Chapter Summary and PracticeA connected review of atomic models, particles, shell structure, valency, isotopes, isobars and calculations
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