Structure Of Atom Class 9 Chemistry Worksheet Pdf
Class 9 Chemistry students should refer to the following printable worksheet in Pdf for Structure Of Atom in standard 9. This test paper with questions and answers for Grade 9 Chemistry will be very useful for exams and help you to score good marks
Class 9 Chemistry Worksheet for Structure Of Atom
CBSE Class 9 Chemistry Worksheet - Structure Of Atom - Practice worksheets for CBSE students. Prepared by teachers of the best CBSE schools in India.
STRUCTURE OF ATOM
1. Name three sub atomic particles of an atom.
2. Define atomic number and mass number.
3. Describe the particle scattering experiment conducted by Rutherford with a diagram.
4. Describe the model of atom given by J.J.Thomson.
5. What are the limitations of J.J.Thomson’s model of an atom?
6. Describe the Bohr’s model of an atom.
7. What are the drawbacks of Rutherford’s model of atom?
8. Atomic number of chlorine atom is 17. What is the atomic number of Cl- ?
9. If number of electrons and protons in an atom is 9 each, what is the atomic number of the element?
10. Write the distribution of electrons in following atoms- carbon, sodium, oxygen, sulphur, lithium, silicon, phosphorous, nitrogen.
11. What is valency? If z = 4, what is the valency of the element?
12. What are valence electrons? Give example to explain, how it helps in finding the valency of an atom.
13. Compare an electron, proton and neutron in terms of charge and mass.
14. define the following: (a) mass number (b) atomic number (c) isotopes (d) isobars
15. Write difference between isobars and isotopes.
Exam Questions NCERT Class 9 Science Chapter 4 Structure of the Atom
Question. Give the postulates of Dalton’s atomic theory.
(i) Every element is composed of extremely small particles called atoms.
(ii) Atoms of a given element are identical, both in mass and properties. Different chemical elements have different kinds of atoms; in particular, their atoms have different masses.
(iii) Atoms cannot be created, destroyed or transformed into atoms of other elements.
(iv) Compounds are formed when atoms of different lements combine with each other in small whole number ratios.
(v) The relative number and kinds of atoms in a given compound are constant.
Question. Give the mass numbers of A and B, What is the relation between the two species?
Ans : Mass number of A = No. of protons + No. of neutrons = 6 + 6 = 12u
Mass number of B = No. of protons + No. of neutrons = 6 + 8 = 14u
The species A and B are isotopes, as they have same atomic number but different mass number.
Question. Name the three subatomic particles of an atom.
Ans : (i) Electrons (negatively charged particles) which revolve around the nucleus.
(ii) Protons (positively charged particles) which are present in the nucleus.
(iii) Neutrons (having no charge) which are present in the nucleus.
Question. Give four characteristics of isotopes.
Ans : All isotopes of an element consist of the same number of protons inside their nuclei. Hence, they have the same atomic number.
(i) All isotopes of an element consist of different number of neutrons in their nuclei. Hence, they have different mass number.
(ii) All isotopes of an element give identical chemical reactions.
(iii) Isotopes of an element have same electronic configuration.
Question. Write the conclusions drawn by Rutherford for the following observation during his scattering experiment :
(i) Most of the alpha-particles passed straight through the gold foil.
(ii) Some alpha-particles getting deflected from their path.
(iii) Very small fraction of alpha-particles getting deflected by 180°.
(i) Most of the space inside the atom is empty.
(ii) It indicates that the positive charge of the atom occupies a very little space.
(iii) All the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.
Question. What is the difference between Rutherford’s atomic model and Thomson’s atomic model?
Ans : Rutherford proposed a model in which electrons revolve around the nucleus in well-defined orbits.
There is a positively charged centre in an atom called the nucleus. He also proposed that the size of the nucleus is very small as compared to the size of the atom and nearly all the mass of an atom is centred in the nuclei. Thomson proposed the model of an atom to be similar to a christmas pudding. The electrons are studded like currants in a positively charged sphere like Christmas pudding and the mass of the atom wassupposed to be uniformly distributed.
Question. Describe the essential properties of the atomic nucleus. Compare these properties with the properties of electron.
Ans : Nucleus is small positively charged centre located in a very small space. An electron is a very small negatively charged particle with well established charge to mass ratio. The charge on electron forms the smallest unit of charge on atomic particles.
Question. Which is much closer to the nucleus of an atom out of K and L shells?
Ans : K shell is much closer to the nucleus of an atom.
Question. The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements is 40. What is the name given to such a pair of elements?
Ans : Isobars.
Question. Name the radioisotope used for examining the circulation of blood in the body.
Ans : Na-24 is the radioisotope used for examining the circulation of blood in the body.
Question. Who discovered proton?
Ans : Goldstein discovered proton.
Question. Name one element, the nucleus of which does not have any neutron.
Ans : Hydrogen.
Question. Write the names of three elementary particles which constitute an atom.
Ans : Electron, proton and neutron.
Question. Which study led to the conclusion that atoms are not indivisible?
Ans : Study of static electricity and the condition under which electricity is conducted by different substances led to the conclusion that atoms are not indivisible.
Question. If K and L shells of an atom are full, then what would be the total number of electrons in the atom? What is the valency of this element? Name the element.
Ans : The maximum numbers of electrons that can occupy K and L shells of an atom are 2 and 8 respectively. Therefore, if K and L shells of an atom are full then the total number of electrons in the atom would be 2 + 8 = 10 electrons. So, the valency of this element is zero. The element is neon (Ne).
Question. Elaborate the postulates put forward by E. Rutherford about the structure of atom based on the a -particle scattering experiment.
Question. State the charge and mass of a neutron.
Ans : Neutron has no charge and its mass is equal to that of a proton.
(i) Most of the space inside the atom is empty because most of the a -particles passed through the gold foil without getting deflected.
(ii) Very few particles are deflected from their path, indicating that positive charge of the atom occupies very little space.
(iii) A very small fraction of particles was deflected by 180°, indicating that all the positive charge and mass of the gold atom were concentrated in a small volume within the atom.
Question. If number of electrons in an atom is 8 and number of protons is also 8, then (i) what is the atomic number of the atom? And (ii) what is the charge on the atom?
Ans : (i) Atomic number = Number of protons = 8
(ii) The charge of the atom is zero, as total numbern of positive charge is equal to total number of negative charge. Number of protons = Number of electrons 8 = 8
Question. What is the limitation of J.J. Thomson’s model of an atom?
Ans : The major limitation of J.J. Thomson’s model is that it does not explain how positively charged particles are shielded from negatively charged particles, without getting neutralized.
Question. Name an element which has one electron, one proton and no neutron.
Ans : Hydrogen atom (1H1) has one electron, one proton and no neutron.
Question. Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have?
Ans : Two.
Question. From the symbol 16S32, give :
(i) Atomic number of sulphur
(ii) Mass number of sulphur
(iii) Electronic configuration of sulphur
(iv) Which of the two elements given would be chemically more reactive? S, Ar
(iii) Electronic configuration : 2, 8, 6.
(iv) Element S, having atomic number 16 is chemically more reactive than element Ar of atomic number 18. It is because the outermost shell of the atom of element S has six electrons only and has to complete its octet, whereas the outermost-shell of the atom of element Ar is completely filled up, i.e., its octet is complete and thus it shows little
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