CBSE BOARD QUESTION BANK( IX Chapter: Structure of an Atom)

QUESTIONS BANK CBSE BOARD PAPER 
Questions: 
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 ?
Questions: 
List three main features of Rutherford’s nuclear model of an atom.

Questions: 
On the basis of the number of protons, neutrons and electrons in the samples given below identify   
(a) the cation     (b) the pair of isobars and            (c) the pair of isotopes.

Sample	Protons	Neutrons	Electrons
A	17	18	16
B	18	19	18
C	17	20	17
D	17	17	17

Questions: 
Composition of the nuclei of two atomic species A and B are given as under :

Particala	A	B
Protons	17	17
Neutrons	18	20

(i) What are the mass numbers of A and B ?  
(ii) How are they related to each other ?
Questions: 
(i) Draw a sketch of Bohr’s model of an atom with three shells.  State the rules followed for writing the number of electrons in different energy shells.
Questions: 
(i) What is the drawback of Rutherford’s model of an atom ?
(ii) Mention the postulates Neils Bohr put forth to overcome the objections raised against Rutherford’s atomic model.
(iii)  Chlorine occurs in nature in two isotopic forms, with atomic masses 35 u and 37 u in the ratio of 3 : 1. Calculate the average atomic mass of chlorine atom.
Questions: 
Name the fundamental particle not present in the nucleus of hydrogen atom.
Questions: 
An element ‘Z’ forms the following compound when it reacts with hydrogen, chlorine, oxygen and phosphorus.   ZH₃ , ZCl₃ , Z₂O₃ and ZP
(a) What is the valency of element Z ?  (b)    Element ‘Z’ is metal or non metal ?
Questions:
 (i Write the formula of the compounds  (a) Calcium sulphate  (b) Aluminium chloride
(ii)The average atomic mass of a sample of an element X is 16.2 u. What is the % of isotopes ¹⁶₈X and ¹⁸₈X in the sample ?
Questions: 
(a)  Give one important application of an isotope of cobalt.
(b) Elements from A to E have in them the distribution of e,p and n as follows.

Elements	Electrons	Neutrons	Protons
A	4	4	3
B	8	9	9
C	18	22	18
D	17	20	17
E	17	18	17

Making use of these data find
(i) cation  (ii) anion  (iii)  a pair of isotopes  (iv) an atom of noble gas

Questions: (a)   State the drawbacks of Rutherford’s model of the atom ? Explain the suggestions  put forward by Neils Bohr in his model of atom to overcome these drawbacks.                
(b) Define isotopes with one example. Write two applications of isotopes.

Questions:
 (a) Write the name of the sub - atomic particle discovered by J. Chadwick. What type of charge occurs on this particle ? In which part of atom this particle is located ?
(b) List three steps of experiment performed by Rutherford for his model of an atom.
(c) Define isobars, write its one example.  (d) Which scientist concluded that size of nucleus is very small as compared to size of an atom ?
Questions: 
What are the
(i) conclusions and (ii) shortcomings of Rutherford’s model of an atom ?
Questions: 
Read the following passage and with your own knowledge answer the following In order to overcome the objections raised against Rutherford’s model of the atom, Neil Bohr put forward the following postulates about the model of an atom.
(i) Only certain special orbits known as discrete orbits of electrons are allowed inside the atom.
(ii) While revolving in discrete orbits the electrons do not radiate energy. Write the following statements in your answer book after completing them :
(a) Atom are made up of        ....................    , .................... and ....................       
(b)  .................... amended Rutherford’s shortcomings.      
(c) Electrons do not radiate energy while revolving in ....................  Orbits
(d) Discrete orbits are also known as ....................             
(e) The  K shell can accommodate ...... Electrons whereas L can accommodate........ Electrons
(f) Atomic mass of an element is the sum of number of ...... and  ..............
Questions: 
 The composition of the nuclei of two atomic species X and Y is given as under :

	X	Y
Protons	6	6
Neutrons	6	8

Give the mass numbers of X and Y.  What is the relationship between these two species ?
Questions: 
(i) How Rutherford proved that positively charged particles are present in the nucleus of an atom ?
(ii) Illustrate in brief the drawbacks of Rutherford’s atomic model.
(iii) The total number of nucleons in the atoms of calcium and argon is 40 and the atomic number of calcium and argon are 20 and 18 respectively. Name the pair of these two elements and also find out the number of neutrons present in the nucleus of argon atom.
Questions: 
(i) State Bohr’s postulates about the model of an atom. Draw a sketch of Bohr’s model of an atom with three shells.
(ii) Mention one use of each of the following : (i) Isotope of cobalt (ii) Isotope of iodine
Questions:   How many electrons, protons and neutrons will be there in an element ¹⁹₉ X ?  What will be the valency of the element?
Questions: 
(a)  List the important observations made by Rutherford from his a–particle scattering experiment.
(b) An element Z contains two naturally occuring isotopes ¹⁷₃₅ Z and ³⁷₁₇ Z . If the average atomic mass of this element be 35.5 u, calculate the percentage of two isotopes.
Questions: 
 (a)   State the three rules proposed by Bohr and Bury regarding distribution of electrons in different orbits of atoms.           
 (b)Given that natural sample of iron has isotopes ⁵⁴₂₆ Fe, ⁵⁶₂₆ Fe and ⁵⁷₂₆ Fe in the ratio of 5%, 90% and 5% respectively. What will be the average atomic mass of iron (Fe)?
Questions: 
(a) Describe the main features of Bohr’s model of an atom. Draw a neat and labelled diagram of energy levels.
 (b)Which of the following pairs are isotopes and which are isobars ? (i)  ⁵⁸₂₆ A , ⁵⁸₂₈B (ii) ⁷⁹₅₈ X , ⁸⁰ ₅₈Y  Give reasons for your choice.
(c) Elements A and B have atomic numbers 18 and 16 respectively. Which of these two would he more reactive and why ?
Questions: 
(a) Describe the main features of Rutherford’s model of an atom. State one major drawback of the model.    (b)The number of protons, neutrons and electrons in particles from A to E are given below :

Particle	Protons	Neutrons	Electrons
A	17	18	17
B	3	4	2
C	18	22	18
D	17	20	17
E	9	10	10

Find a pair of isotopes from the above particle by giving suitable reason.
(c) If K and L shells of atoms are full then what would be the total number of electrons in the atom ?
Questions:  (a) Enlist the three conclusions made by the Rutherford from his α - ray scattering experiment.
(b)What were the drawbacks of Rutherford’s model of an atom ?
Questions: 
(a) What are the postulates of Bohr’s model of an atom ?
(b) Show diagrammatically the electron distributions in Sodium, Lithium and Aluminium atoms.

Guess paper:Chapter: Structure of an Atom

Q.1 What was the model of an atom proposed by Thomson?
Q.2 What is the nature of charge on electrons?
Q.3 What are canal rays ?
Q.4 State the nature of the constituents of canal rays.
Q.5 Who discovered the nucleus of the atom?
Q.6 What is the charge on alpha particles ?
Q.7 Which observation of Rutherford’s scattering experiment established the presence large empty space in atom? Read more

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9th Class NCERT Solution Chapter: Structure of Atom

Questions:  Explain with examples (i) atomic number (ii) mass number (iii) isotopes and (iv) isobars.  Give any two uses of isotopes.

Ans. (i) Atomic number : The number of protons in the nucleus of an atom is called its atomic number.

Example : Chlorine has 17 protons in its nucleus, therefore, its atomic number is 17.

(ii) Mass number : The number of protons and neutrons present in the nucleus of an atom is known as its mass number.

Example : Sodium has 11 protons and 12 neutrons in its nucleus, therefore, its mass number is (11 + 12) = 23.

(iii) Isotopes : Atoms of the same element having the same atomic number but different mass numbers are called isotopes.

Example : Chlorine has two isotopes ³⁵₁₇Cl and ³⁷₁₇ Cl , in which atomic number is 17 for both, but mass numbers are 35 and 37.

(iv) Isobars : Atoms of different elements having the same mass number, but different atomic numbers are known as isobars.

Example : Calcium and argon atoms have the same mass number 40, but different atomic numbers 20 and 18 respectively.

Uses of Isotopes

1. Isotope of uranium ²³⁵₉₂U is used as a nuclear fuel in atomic reactors.

2. Cobalt – 60, an isotope of cobalt is used in the treatment of cancer.

3.Isotopes of iodine is used to treat goitor

Questions: Na+ has completely filled K and L shells. Explain.

Ans. Na loose 1 electron to form sodium ion Na+ . So, Na⁺ ion has one electron less than Na atom i.e., it has 10 electrons.  Therefore, Electronic configuration of Na⁺ = 2,8  completely filled k(2) and(8) l shells

Questions: If bromine atom is available in the form of, say, two isotopes ⁷⁹₃₅ Br (49.7%) and ⁸¹₃₅ Br (50.3%), calculate the average atomic mass of bromine atom.

Ans:  The average atomic mass of bromine atom = 49.7% of 79 + 50.3% of 81= 39.263+40.743 = 80.006 u = 80 u,

Questions: The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ¹⁶ ₈ X and ¹⁸₈ X in the sample?

Ans. Let the percentage of isotope ¹⁶ ₈ X be  y%. then,  the percentage of isotope ¹⁸₈ X  will be (100 − y) %.

Therefore,  16.2 =  16 x y/100 + 18 x (100-y)/100

16.2 =  16y/100 + (1800 - 100y)/100

16.2 x100 = 16y+1800 - 18y

1620 -1800 = -2y

-180/-2 = y = 90

So, ¹⁶ ₈ X = 90%  and  ¹⁸ ₈ X     = 10%

Questions: If Z = 3, what would be the valency of the element? Also, name the element.

Ans: Z = 3, we mean that the atomic number of the element is 3. Its electronic configuration is 2, 1. Hence, the valency of the element is 1 Therefore, the element with Z = 3 is lithium.

Page 47 

 1. What are canal rays? Ans: Canal rays are positively charged radiation s that can pass through perforated cathode plate. Th... Read Full NCERT Solution

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