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CBSE - Class 9 Science Structure of the Atom Worksheet

1.
For the following statements, write T for True and F for False.
(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
2.
If bromine atom is available in the form of, say, two isotopes $^{79}_{35}Br$ (49.7%) and $^{81}_{35}Br$ (50.3%), calculate the average atomic mass of bromine atom.
3.
Describe Bohr’s model of the atom.
4.
The average atomic mass of a sample of an element $X$ is 16.2 u. What are the percentages of isotopes $^{16}_8X$ and $^{18}_8X$ in the sample?
5.
Define valency by taking examples of silicon and oxygen.
6.
Explain with examples (i) Atomic number. Give any two uses of isotopes.
7.

Number of valence electrons in $Cl^-$ ion are:

a.

16

 b.

8

 c.

17

 d.

18
8.
Explain with examples (ii) Mass number. Give any two uses of isotopes.
9.
Explain with examples (iii) Isotopes. Give any two uses of isotopes.
10.
For the following statements, write T for True and F for False.
(c) The mass of an electron is about $\frac{1}{2000}$ times that of proton.
11.
Compare the properties of electrons, protons and neutrons.
12.
Which one of the following is a correct electronic configuration of sodium?
a. (a) 2,8 b. (b) 8,2,1 c. (c) 2,1,8 d. (d) 2,8,1.
13.
What are the limitations of J.J. Thomson’s model of the atom?
14.
For the following statements, write T for True and F for False.
(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.
15.
Compare all the proposed models of an atom given in this chapter.
16.

Complete the following table. 

Number of valence electrons in Cl ionis

17.

Rutherford’s alpha-particle scattering experiment was responsible for the discovery of

a.

Atomic Nucleus

 b.

Electron

 c.

Proton

 d.

Neutron
18.
Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.
19.

Isotopes of an element have

a.

the same physical properties

 b.

different chemical properties

 c.

different number of neutrons

 d.

different atomic numbers.
20.
If $Z = 3$, what would be the valency of the element? Also, name the element.

Worksheet Answers

7.
12.
17.
19.
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