Structure of atoms class 9 worksheet

Given below are the CBSE Structure of atoms class9 worksheet
(a) Fill in the blank's
(b) True and False
(c) Very short answer type
(d)Short answer type
(e)Long answer type
(f) Foundation level
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Fill in the blanks:

Question 1.
  1. According to Maharishi Kanad, the tiniest to tiny particle of a pure substance is called _________.
  2. An atom is the smallest unit of an element which takes part in a _________.
  3. Mass of an electron is 1/1837 times less than the mass of one atom of__________.
  4. The K-shell of any atom cannot have more than _________ electrons.
  5. Isotopes are the atoms of ___________ element, having same atomic number but different mass number.
  6. An atom of an element has 11 protons 11 electrons and 12 neutrons. The atomic mass of the atom is __________.
  7. Almost all the mass of an atom is concentrated in a small region of space called the _______.
  8. The subatomic particle not present in a hydrogen atom is________.
  9. Cathode ray are a beam of fast moving ______ .
  10. ________and________ more or less complexly make up the mass of an atom.
  11. The number of neutrons in the neutrons in the neutrons of an atom can be calculated by _______ the atomic number of _______its mass number.
  12. The isotopes of an element do not differ in the number of _______ but do differ in the number of _______.
  13. The type of radiations, which are not deflected in presence of electric or magnetic field are termed as rays.
  14. The penetrating power of B-rays is_______ times more than a-rays.
  15. Synthetic elements are those which are prepared by _________.
  16. The control rods in a nuclear reactor are made up of _________.
  17. _______ are stored in deep mines which are not in use.
  18. When an elements emits B-particle, its mass number________.
  19. Y-rays are________ radiations.
  20. The difference between the actual isotopic mass and the sum of masses of protons, neutrons and electrons is called_________.
  21. _______ are the best dombarding particles.
  22. ________ is used for the treatment of leukaemia.


Fill in the blanks:

  1. Anu
  2. Chemical reactin
  3. Hydrogen
  4. Two
  5. Same
  6. 23
  7. Nucleus
  8. Neutron
  9. Electrons
  10. Proton, neutron
  11. Eight
  12. Subtracting, from
  13. Gamma
  14. 100
  15. Artificial transmutation
  16. Cadmium
  17. Radioactive material
  18. Remains unchanged
  19. Electromagnetic
  20. Mass detect
  21. Neutrons
  22. Phosphorus

True and False

Question 2.
  1. Radioactive isotope of iodine is used for making the medicine called tincture iodne.
  2. Thomson proposed that the nucleus of an atom contains protons and neutrons.
  3. J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
  4. An electron has a mass that is much less than a proton.
  5. There is no particle of matter smaller than an atom.
  6. Atoms of an element may have more or less neutrons or electrons than other atoms of the same element.
  7. The innermost atomic shell can hold a maximum of 18 electons.
  8. B- Particles are fast moving electrons carrying negative charge.
  9. Nuclear chemistry has nothing to do with the electrons present in an atom.
  10. B- particles are nothing but electrons.
  11. a-particles are same thing as helium atoms.
  12. Out of a, B and y- rays travel with the highest speed and have highest ionizing power.
  13. A loss of B-particle result n the production of isobars.
  14. There is no difference between ‘artificial radioactivity’ and ‘induced radioactivity’.
  15. Iodine- 131 is used in the treatment of thyroid disorders.
  16. In a given electric field, B-particles are deflected more than a- particles in spite of a- particles having larger charge.


True / False:

  1. False
  2. False
  3. False
  4. True
  5. False
  6. True
  7. False
  8. True
  9. True
  10. True
  11. True
  12. True
  13. True
  14. True
  15. True
  16. True

Very Short anwer type

Question 3.
Who discovered the neutral particles present in an atom?


J. Chadwick

Question 4.
What conclusion would you derive from the observation, that in Rutherford's scattering experiment, most of the alpha- particles passed through gold foil without any deflection?


(a)Most of the space inside the atom is empty because most of the alpha-particles passed through the gold foil without getting deflected.
(b)Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.

Question 5.
Which shell is closest to the nucleus of an atom?


K shell

Question 6.
Which energy level would accommodate the 17th electron?
Question 7.
Select the isotopes from the following?
21/10A; 22/10B; 23/11C; 23/12D

Short Answer type

Question 8.
If an atom contains one electron and one proton, will it carry any charge or not?
Question 9.
If K and L shells of an atom are full, then what would be the total number of electrons in the atom?
Question 10.
Hydrogen exists in the three isotopic forms. Why are the isotopes of hydrogen chemically alike?
Question 11.
Why alpha- particle scattering experiment was possible by using gold foil only and not by foil of any other metal?
Question 12.
Write electronic configuration of the following elements and predict their valencies:
(a)Fluorine: 9
(b)Aluminium: 13
(c)Argon: 18

Long Answer type

Question 13.
Define the term valency? How is it different from valence electrons? Find the valency of oxygen and fluorine?
Question 14.
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?
Question 15.
Which of the two elements given below would be chemically more reactive:
'X' of atomic number 18 or element Z of atomic number 16? And why?
Question 16.
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).
Question 17.
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.
Question 18.
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?

Foundation Level

Question 19.
Name the following processes:
(i)13AI27 + 2He4 -> 15P30 + 0n1 ->14Si30 + 1e0
(ii)5B10 + 2He4->7N13 + 0n1 ->6C13 + 1e0
(ii)5B10 + 2He4 -> 6C13 + 1e0
Question 20.
Complete the nuclear reaction expression:
(i)59/27Co (d, p)…………
(ii)27/13AI (a, n)………...
Question 21.
Complete the following nuclear reaction equations by supplying the missing information:
(i)23/11Na +……. _____23/12Mg + 1/0n
(ii)27/13AI +…….______30/15P + 1/0n


This Structure of atoms class9 worksheet with answers is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.

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