CBSE Important Questions(Long questions) for Structure of atoms

Given below are the Class 9 Science Important Questions for CBSE Important Questions(Long questions) for Structure of atoms

a) Concepts questions
b) Calculation problems
c) Multiple choice questions
d) Long answer questions
e) Fill in the blank's

1. Helium atom has two electrons in its valence shell but its valency is not two. Explain?
2. Draw a diagram of the Thomson’s model of an atom. Why was it discarded?
3. What are the differences between isotopes and isobars?
4. Compare all proposed models of an atom?
5. An ion M+3  has 10 electrons and 14 neutrons. Find its atomic number and mass number of M?
6. Magnesium has 12 protons and 12 neutrons. Fid the valency of magnesium?
7. Write the conclusions drawn by Rutherford for the following observing during his alpha scattering experiment:
a) Most of the alpha- particle passed straight through the gold foil.
b) Some alpha- particles getting deflected from their path.
c) Very small fraction of alpha- particles getting deflected by 180C.
8. An element is represented as  8X16  Find:
a) The number of electrons in element X.
b) Mass number of an element X.
c) The number of neutrons in element X.
9. With the help of labeled diagram describe in brief the Rutherford’s experiment. Write any three important conclusions drawn from the experiment?
10. The average atomic mass of a sample of element X is 16.2u. What are the percentage of isotopes  8X16   and  8X18   respectively?
11. State the major drawback in Rutherford’s model which helped compensate this drawback?

12. List three differences between electron, proton and neutron?
13. Compare the K and K+ ion on the following parameters:
a) Number of electrons
b) Electronic configuration
c) Atomic structure (energy shells)
14. Give reasons of following:
a) An atom is electrically neutral.
b) Ions are more stable than atoms.
c) Noble gases show low reactivity.
15. Name two elements which have isotopes. Write the symbol of their isotopes and provide an account of the sub-atomic particles present in each of these isotopes.
16. Calculate the number of electrons, protons and neutrons in an atom of an element with atomic number 20 and mass number 40. Write electronic configuration and draw the structure of the atom?
17. An atom has complete K and L shells. Is this an atom of a metal, non-metal or noble gas? Justify?
18. Define the term valency? How is it different from valence electrons? Find the valency of oxygen and fluorine?
19. Write electronic configuration of the following elements and predict their valencies:
a) Fluorine: 9
b) Aluminium: 13
c) Argon: 18
20. What will be the composition of nucleus of the atom of an element with atomic number 19 and mass number 39? Also write its electronic configuration?
21. Which of the two elements given below would be chemically more reactive:
22. ‘X’ of atomic number 18 or element Z of atomic number 16? And why?
23. An element has electronic configuration of 2,8,7:
a) What is the atomic number of the element?
b) What is the name of the elements?
c) Which of the following elements have same number of valence electron? N(7), F(9), P(15) and Ar(18).
24. State reasons for the following statements:
a) Some elements possess fractional atomic mass.
b) Isotopes of an element have similar chemical properties.
c) Noble gases are inert.
25. There are two elements A1326 and B1426. Find the number of sub-atomic particles in each of these elements. What is the relationship between the two?




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