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CBSE - Class 9 Science Structure of the Atom Worksheet

1.
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.
2.

Isotopes of an element have

a.

the same physical properties

 b.

different chemical properties

 c.

different number of neutrons

 d.

different atomic numbers.
3.
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.
4.
$Na^+$ has completely filled $K$ and $L$ shells. Explain.
5.
Explain with examples iv) Isobars. Give any two uses of isotopes.
6.
If $Z = 3$, what would be the valency of the element? Also, name the element.
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.
What are the limitations of Rutherford’s model of the atom?
10.
Describe Bohr’s model of the atom.
11.
Explain with examples (i) Atomic number. Give any two uses of isotopes.
12.
Define valency by taking examples of silicon and oxygen.
13.
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?
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.
Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.
16.
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.
17.
Compare all the proposed models of an atom given in this chapter.
18.
Explain with examples (iii) Isotopes. Give any two uses of isotopes.
19.
What are the limitations of J.J. Thomson’s model of the atom?
20.

Composition of the nuclei of two atomic species $X$ and $Y$ are given as under

Give the mass numbers of $X$ and $Y$. What is the relation between the two species?

Worksheet Answers

2.
3.
7.
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