class 9

class 9 science chapter 4 important questions

  1. What are cations and anions.
  2. What is Thomson’s model of atom? What is its drawback?
  3. What are isobars? Comment on their physical and chemical properties.
  4. Give any three important characteristics of cathode rays.
  5. Give any two proofs to show that electrons are universal constituent of all atoms.
  6. What was drawback of Ruttherford’s model of atom?
  7. How was electron discovered? Explain briefly.
  8. How was proton discovered? Explain briefly.
  9. Write the important features of Bohr’s model of atom.
  10. How was neutron discovered? Explain briefly.
  11. What are isotopes? Give their important applications.
  12. Write the electronic configuration of potassium atom (Atomic number of potassium=19). What will be its valency?
  13. Write the isotopes of hydrogen and give their names.
  14. What do you think would be the observation if the alpha-particle scattering experiment is carried out using a foil of a metal other than gold?
  15. Which isotope is used in the treatment of cancer?
  16. The atom of an element has 2 electrons in the M-shell. What is its atomic number? Name the element.
  17. On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.
  18. What do you understand by ground state and excited state of an atom?
  19. Give at least three proofs to show that electrons are present in all atoms.

most important questions, class 9, chapter 3

  1. State the location of electrons and protons in an atom.
  2. Which of the two atomic numbers or atomic mass determines the chemical properties of an element?
  3. What is an orbit, shell or energy level?
  4. What is a valence shell?
  5. What are valence electrons?
  6. Write the electronic configuration of an element X whose atomic number is 12.
  7. What is the maximum number of electrons an M shell of the atom can accommodate?
  8. If both K and L shells of an atom are full,what is the total number of electrons contained in them?
  9. Write the electronic configuration of the element with atomic number 20.Indicate the valency of the element.
  10. How many electrons will be present in K,L and M energy shells of atoms of elements with atomic numbers (i) 11 and (ii) 18?
  11. Who discovered anode (canal) rays?
  12. Which the lighter. A proton or an electron?
  13. Name the gas which gives the lightest positively charged particle.
  14. Name the fruit which resembles Thomson model of atom.
  15. Which metal foil was used by Rutherford in his experiment for the discovery of nucleus?
  16. Electron in an atom jumps from K to L shell. Will the energy be absorbed or evolved?

Changing of solid to liquid state (melting)

When a solid is heated it starts melting at a certain fixed temperature (melting point). At this stage even when the heating is continued, the temperature does not change until the whole of solid is converted into liquid. The state when solid and liquid phases of a substance coexist is called solid-liquid equilibrium. Solid-liquid equilibrium is described as,

  • If no heat is exchanged with the surroundings, then the temperature and the mass of the two phases (solid and liquid) remain constant.

For example, if we place ice and water at 273 K (0°C) under normal atmospheric pressure in a perfectly insulated thermos flask, since the flask is insulated, there will be no exchange of heat between its contents and the surroundings. We notice that

  • The temperature of both the phases remains constant, i.e., temperature of the system does not change.
  • Mass of each phase (ice and water) does not change with time.

Rate of transfer of molecules from ice to water = Rate of transfer of molecules from water to ice