CHAPTER-4 STRUCTURE AND ATOMS (CLASS-9th) SCIENCE

Chapter Structure and Atoms

  1. Which subatomic particle is absent in an ordinary hydrogen atom?
  2. J. Chadwick discovered a subatomic particle which has no charge and has mass nearly equal to
    that of a proton. Name the particle and give its location in the atom.
  3. Is it possible for the atom of an element to have one electron, one proton and no neutron? If so, name the element.
  4. Electron attributes negative charge, protons attribute positive charge. An atom has both but why there is no charge?
  5. Which of the following pairs are isotopes?
    (i) 20984x,21084x
    (ii) 23290Z,23191Z
  6. Out of elements 3417X and 4018Y, which is chemically more reactive and why?
  7. One electron is present in the outermost shell of the atom of an element X. What would be the
    nature and value of charge on the ion formed if this electron is removed from the outermost shell?
  8. The atomic number of Al and Cl are 13 and 17, respectively. What will be the number of
    electrons in Al3+ and Cl–?
  9. Write down the electron distribution of chlorine atom. How many electrons are there in the L
    shell? (Atomic number of chlorine is 17).
  10. Define valence electrons. Which electrons of an atom are involved in the chemical bond
    formation with other atoms?
  11. Find out the valency of the atoms represented by the Figs. (a) and (b) [NCERT Exemplar]figure 11.1 Class 9th Science Chapter 4
  12. Identify the Na+ ion from the following figures. What is the valency of sodium atom? Give reason.Figure 12 Class 9th Science Chapter 4
  13. In the gold foil experiment of Geiger and Marsden, that paved the way for Rutherford’s model of an atom, ~ 1.00% of the a-particles were found to deflect at angles > 50°. If one mole of aparticles were bombarded on the gold foil, compute the number of a-particles that would deflect at angles less than 50°.
  14. Predict the valency of the following elements
    (i) A (Atomic number 5)
    (ii) B (Atomic number 12)
    (iii) C (Atomic number 14)
    (iv) D (Atomic number 17)
  15. An element ‘X’ contains 6 electrons in ‘M’ shell as valence electrons:
    (a) What is the atomic number of ‘X’?
    (b) Identify whether ‘X’ is a metal or non-metal.
  16. What is the gold foil experiment? Name the scientist who performed this experiment. Write the
    conclusions and shortcomings of Rutherford’s model of atom.
  17. In what way is the Rutherford’s atomic model different from that of Thomson’s atomic model?
  18. What are the postulates of Bohr’s model of an atom?
  19. The ratio of the radii of hydrogen atom and its nucleus is ~105. Assuming the atom and the
    nucleus to be spherical,
    (i) what will be the ratio of their sizes?
    (ii) If atom is represented by planet Earth ‘Re’ = 6.4 × 106 m. Estimate the size of the nucleus.
  20. Calculate the number of neutrons present in the nucleus of an element X which is represented
    as 3115X
  21. Why do isotopes show similar chemical properties?
  22. An element ‘X’ has a valency 3(+):
    (a) Write the formula of its phosphide.
    (b) Write the formula of its carbonate.
  23. List any three distinguishing features between the models of an atom proposed by J.J. Thomson and Ernest Rutherford.
  24. An element ‘X’ contains 6 electrons in ‘M’ shell as valence electrons:
    (a) What is the atomic number of ‘X’?
    (b) Identify whether ‘X’ is a metal or non-metal.
  25. In the atom of an element ‘Z’, 5 electrons are present in the outermost shell. It requires noble gas configuration by accepting requisite number of electrons, then what would be the charge on the ion so formed? Write the formula of the compound which will be formed when ‘Z’ reacts with Na atom.
  26. 222 86 Rn is an isotope of noble gas, radon. How many protons, neutrons and electrons are there in one atom of this radon isotope?
  27. What information do you get from the figures about the atomic number, valency of atoms X, Y
    and Z? Give your answer in a tabular form.Figure 27 Class 9th Science Chapter 4
  28. Write the molecular formulae for the following compounds:
    (a) Copper (II) bromide
    (b) Aluminium (III) nitrate
    (c) Calcium (II) phosphate
    (d) Iron (III) sulphide
    (e) Mercury (II) chloride
    (f) Magnesium (II) acetate
  29. Write the molecular formulae of all the compounds that can be formed by the combination of
    following ions Cu2+, Na+, Fe3+, Cl–, so2−4,PO3−4
  30. Write the formula of the compounds formed by the following ions.
    (a) Mg2+ and S2-
    (b) Cu2+ and OH
    Name the compounds formed in each case.

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