CBSE · Class 9 · Science · Chapter 9

Atomic Foundations of Matter

Learn how atoms combine to form molecules and compounds using chemical symbols, formulae and atomic relationships.

14 lessons 55 min
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Lessons in this chapter

  1. 1Law of Conservation of MassNothing vanishes in a reaction; the trick is making sure the whole system stays on the scale.
  2. 2Law of Constant ProportionsA pure compound keeps the same mass ratio of its elements no matter where the sample came from.
  3. 3Dalton's Atomic TheoryThe laws of chemical combination make sense when reactions are viewed as rearrangements of tiny atoms.
  4. 4How Atoms Combine?Atoms form stable groupings by sharing or transferring valence electrons, creating chemical bonds.
  5. 5Bonding by Sharing of Electrons — Covalent BondHydrogen, chlorine and oxygen show how one or more shared electron pairs can hold atoms together.
  6. 6Molecules of CompoundsDifferent elements share electrons to form hydrogen chloride, water and other covalent molecules.
  7. 7Naming Covalent CompoundsA prefix system turns molecular formulae into systematic names while preserving familiar common names.
  8. 8Bonding by Electron Transfer — Ionic BondElectron transfer creates cations and anions whose opposite charges attract.
  9. 9Naming Ionic CompoundsIonic compounds are extended ion lattices, and their names identify cations and anions.
  10. 10Writing Chemical FormulaeValencies and ionic charges can be crossed, simplified and grouped to write correct compound formulae.
  11. 11Properties of the Ionic and the Covalent CompoundsSolubility, conductivity and melting behaviour reveal important differences between ionic and covalent substances.
  12. 12Molecular Mass of Covalent CompoundsA molecular formula becomes a mass calculation when each atomic mass is multiplied by its atom count and the contributions are added.
  13. 13Formula Unit Mass of Ionic CompoundsIonic crystals use formula units, so their mass is calculated from the simplest whole-number ion ratio.
  14. 14Chapter Summary and PracticeEvery law, bond, formula and mass calculation returns for one connected review.
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