CBSE Class 9 Science Structure Of Atom Worksheet

CBSE Class 9 Science Worksheet - Structure of Atom. Students can download these worksheets and practice them. This will help them to get better marks in examinations. Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

1 Mark Questions:

1.On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole?

2.Where are electrons found in the atom?

3. What are canal rays?

3.Why is the nucleus of an atom positively charged?

4.Why did Rutherford select a gold foil in his α-ray scattering experiment?

5. If Mg2+has 12 protons and 12 neutrons,what is its atomic number and mass number? (CBSE 2010)

6.What are the limitations of Rutherford's model of the atom?

7.Define valency and Give an example of a monovalent element.

8.An atom of an element has 7 electrons in its L shell,name the element and write it's atomic number?

9.Why Mg atom gets 2+ charge when it loses two electrons ?

10.Name the particles which determine the mass of an atom.

11.Which of the following are isotopes and which are isobars? Argon, Protium, Calcium, Deuterium.

2 Mark Questions:

1.What observations in a scattering experiment led Rutherford to make the following observations:

i) Most of the space in an atom is empty.

ii) Nucleus is positively charged.

iii)Whole mass of an atom is concentrated in its centre.

2.Mention any two drawbacks of Rutherford’s model.

3. State the characteristics of nucleus of an atom.

4. Describe Bohr’s model of the atom?

5.The atomic number of chlorine is 17 and mass number is 35.

a. What would be the electronic configuration of a negatively charged chloride ion, Cl- ?

b. What would be the atomic number and mass number of Cl- ?

6.What is electronic configuration and how is the valency of an atom related to it ?

7.Which of the two would be chemically more reactive element,X of atomic number 18 or element Z of atomic number 16 and why?

8.What are isotopes? Why do isotopes show similar chemical properties but they differ in physical properties?

9.Write isotopes of uranium and its uses.

10.Write one pair of Isobars. Why the chemical properties of isobars are not similar?

3 Mark Questions:

1. Explain Rutherford's gold foil experiment with diagram

2.Write three points of difference between isotopes and isobars.

3.The average atomic mass of a sample of an element ‘X’ is 16.2μ. What is the percentage of each isotope 16X and 18X in the sample?( At.No. of X =8)

4.Define valency of an element. Find the valency of chlorine and magnesium.

5.i)What is the similarity in the electronic structure of the following set of atoms?

Lithium, sodium and potassium.

ii) Which of the above element is most reactive and why?

6.Complete the following table.

Element At. No. Mass No. Protons Neutrons Electrons

A 11 - - 12 -

B - 35 - - 17

C - - 9 10 -

D - 20 - - 10

7.Give reason for the following

a) An atom is electrically neutral

b) Noble gases show least reactivity

c) Nucleus of an atom is heavy and positively charged.

d) Ions are more stable than atoms.

8. An element has an atomic number 12 and mass number 26.Draw a diagram showing the

distribution of electrons in the orbits and the nuclear composition of the neutral atom. If this

element X combines with another element Y whose electronic configuration is 2,8,7, what will be the formula of the compound thus formed? (CBSE CCE 2010)

9. Name the Scientists who have contributed the following towards the understanding of the atomic structure.

i) Discovery of electrons

ii) Canal rays

iii) Concept of nucleus

iv) Stationary orbits

v) Indivisibility of atoms

vi) Neutron

Value Based Question :

1.In Kaiga nuclear Power Corporation building,drinking water was found to be contaminated with tritium .

It is highly radioactive.

a) What is tritium? Write its atomic number and mass number.

b) It is an isotope of which element?

c) Name the other two isotopes of the same element.

d) What precautions do you suggest so that this type of incident does not occur again?

e) What is meant by radioactive?

2. Most of the children burst crackers during diwali.It creates a lot of noise pollution and air pollution.

Asthma patients have tough time during diwali.Many children get hurt due to mishandling of fire crackers.Poisonous gases like sulphur dioxide ,phosphorous pentoxide are formed.

a) Name two elements present in gun powder used in crackers.

b) Government has banned bursting of fire crackers after 10pm.Do you agree? Give reason.

c) Why should we not wear synthetic clothes while bursting crackers?

 Exam Questions NCERT Class 9 Science Chapter 4 Structure of the Atom

Question. Name the scientist who discovered neutrons.
Ans : J. Chadwick.

Question. What was Chadwick’s experiment?
Ans : In Chadwick’s experiment, he bombarded beryllium atoms with high speed particles.
(i) The rays emitted from beryllium during bombardment had speeded about one-tenth the speed of light.
(ii) Later Chadwick was able to show that these rays consisted of neutral particles called neutron.

Question. Which shell can accommodate a maximum of 32 electrons?
Ans : Fourth shell can accommodate a maximum of 32 electrons.

Question. Define the term “Half life”.
Ans :
Radioactive elements are unstable and disintegrate with time emitting alpha and beta particles along with gamma rays. The rate of disintegration depends on the amount of substance. As the amount of the substance decreases, disintegration becomes slower. But it takes a long time for whole of the substance to decay. Thus, the rate of radioactive decay is measured
in terms of half time. The time taken by half of the atoms of radioactive element to disintegrate is called its half-time.

Question. What is the mass of a neutron?
Ans : The mass of a neutron is 1.675 × 10–24 g.

Question. What is the charge and mass of a -particles?
Ans : Charge is 2 and mass is 4 amu.

Question. What is the charge and mass of alpha particle?
Ans : Charge = + 2 units
Mass = 4 units

Question. Explain Rutherford’s atomic model.
Ans : Rutherford purposed a model of an atom on the basis of a-particles scattering experiment. This is known as Rutherford’s nuclear model of atom.
(i) An atom consist, a heavy positively charged core called nucleus.
(ii) Nucleus is surrounded by electrons.
(iii) Electrons and nucleus are held together by electrostatic force of attraction.
(iv) Size of nucleus is very small as compared to the size of atom.
(v) Almost the entire mass of the atom is concentrated in the nucleus.

Question. Name the particles which determine the mass of an atom.
Ans : Proton and neutron are the particles which determine the mass of an atom.

Question.Why did Rutherford select a gold foil in his a-ray scattering experiment?
Ans : Rutherford selected a gold foil in his a-ray scattering experiment because gold has high malleability and can be hammered into thin sheet.

Question. Electron attributes negative charge, protons attribute positive charge. An atom has both but why there is no charge?
Ans : The negative and positive charges of electrons and protons respectively are equal in magnitude. So, the atom as a whole is electrically neutral.

Question. Write the charge and mass of an electron.
Ans : Its mass is 2000 1 times that of proton and it is negatively charged.

Question. What are nucleons?
Ans : Protons and neutrons reside in the nucleus of an atom and are thus called nucleons.

Question. An element 12X24 loses two electrons to form a cation which combines with the anion of element 17Y35 formed by gaining an electron.
(i) Write the electronic configuration of element X.
(ii) Write the electronic configuration of the anion of element Y.
(iii) Write the formula for the compound formed by combination of X and Y.
Ans :
(i) X = 2, 8, 2
(ii) Y = 2, 8, 8
(iii) XY2

Question. Why isotopes of an element are chemically similar?
Ans : Isotopes of an element are chemically similar because these have same electronic configuration.

Question. What is an orbit?
Ans : Orbit is the path of electron around the nucleus.

Question. (i) An ion X2+ contains 10 electrons and 12 neutrons. What is the atomic number and mass number of the element X?
(ii) Is it possible in an atom to have 12 protons and 13 electrons?
(iii) Why helium gas is inert?
Ans : (i) Atomic number = 12, Mass number = 24.
(ii) No, it is not possible. An atom is electrically neutral. The number of positively charged particles (protons) is always equal to the number of negatively charged particles (electrons).
(iii) Helium atom has completely filled outermost shell. Thus, it is inert.

Question. What were the drawbacks of Rutherford’s model of an atom?
Ans : The orbital revolution of the electron is not expected to be stable. Any particle in a circular orbit would undergo acceleration and the charged particles would radiate energy. Thus, the revolving electron would lose energy and finally fall into the nucleus. If this were so,
the atom should be highly unstable and hence matter would not exist in the form that we know.

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