Samacheer Kalvi 9th Science Books English Medium Atomic Structure

Science : Chapter 11 : Atomic Structure

I. Multiple Choice Questions

1. Among the following the odd pair is

Ans ; c

2. Change in the number of neutrons in an atom changes it to

1. an ion
2. an isotope.
3. an isobar
4. another element.

Ans ; an isotope

3. The term nucleons refer to

1. Protons and electrons
2. only Neutrons
3. electrons and neutrons
4. Protons and neutrons

Ans ; Protons and neutrons

4. The number of protons, neutrons and electrons present respectively in

1. 80, 80, 35
2. 35, 55, 80
3. 35, 35, 80
4. 35, 45, 35

Ans ; 35, 45, 35

5. The correct electronic configuration of potassium is

1. 2,8,9
2. 2,8,1
3. 2,8,8,1
4. 2,8,8,3

Ans ; 2,8,8,1

II. True or False if false give the correct answer:

1. In an atom, electrons revolve around the nucleus in fixed orbits. ( True )

2. Isotopes of an element have the different atomic numbers. ( False )

Ans : They have different mass numbers.

3. Electrons have negligible mass and charge. ( True )

4. Smaller the size of the orbit, lower is the energy of the orbit. ( True )

5. The maximum number of electron in L shell is 10. ( False )

Ans : The maximum number of electrons in L shell is 8.

III. Fill in the Blanks:-

1. Calcium and Argon are examples of a pair of _________________

Ans : Isobars

2. Total Number of electrons that can be accommodated in an orbit is given by ______________

Ans : 2n²

3. _____________ isotope is used in the treatment of goiter

Ans : Iodine -131

4. The number of neutrons present in is ___________

Ans : 4

5. The valency of Argon is ___________

Ans : Zero

IV. Match the following

i)

1. Dalton	Hydrogen atom model
2. Thomson	Planetary model
3. Rutherford	First atomic theory
4. Neils Bohr	Plum pudding model
	Discovery of neutrons

Ans ; 1 -C, 2 – D, 3 – B, 4 – A

ii)

1. Mass of proton	1.6 X 10-19 C
2. Mass of electron	-1.6 X 10-19 C
3. Charge of electron	9.31 X 10-28 g
4. Charge of proton	1.67 X 10-24 g

Ans ; : 1 – D, 2 – C, 3 – B, 4 – A

V. Complete the following table :

Atomic Number	Mass Number	Number of Neutrons	Number of Protons	Number of Electrons	Number of the Element
9	19	10	9	9	Fluorine
16	32	16	16	16	Sulphur
12	24	12	12	12	Magnesium
1	2	1	1	1	Deuterium
1	1	0	1	1	Protium

VI. Arrange the following in the increasing order of atomic number:

Calcium, Silicon, Boron, Magnesium, Oxygen, Helium, Neon, Sulphur, Fluorine and Sodium

Helium < Boron < Oxygen < Fluorine < Neon < Sodium < Magnesium < Silicon < Sulphur < Calcium

VIII. Very short answer

1. Name an element which has the same number of electrons in its first and second shell.

Beryllium (2,2)

2. Write the electronic configuration of K⁺ and Cl^–

Electronic configuration of K⁺ is (2,8,8)

Electronic configuration of Cl^– is (2,8,8)

So, they are Iso-electonic.

3. Compare the charge and mass of protons and electrons.

Particle	Charge	Mass
Proton	1.602 x 10-19C	1.672 x 10-24g
Electron	1.602 x 10-19C	9.108 x 10-24g

4. For an atom ‘X’, K, L and M shells are completely filled. How many electrons will be present in
it?

Total number of electrons	= K + L +M
	= 2+8+18=28

5. Ca²⁺ has completely filled outer shell. Justify your answer.

Ca has electronic configuration 2,8,8,2. After losing 2 c-s it becomes 2,8,2 (completely filled outer shell.
Ca -2e → Ca²⁺

2,8,8,2 2,8,8 (completely filled)

IX. Short answer

1. State the law of multiple proportion?

When two elements A and B combine together to form more than one compound, then masses of A which separately combines with a fixed mass of B are in simple ratio.

2. List the uses of isotopes?

• Cobalt-60 isotope is used in the treatment of Cancer.
• Uranium -235 acts as a fuel in nuclear reactors.

3. What is isotone? Give an example?

Atoms of different elements with

• Different atomic numbers
• Different mass numbers.
• Same number of neurtrons.

4. Calculate the number of neutrons, protons and electrons.

• atomic number 3 and mass number 7
• atomic number 92 and mass number 238

Element	Neutrons	Protons	Electrons
3X7	24	3	3
92X238	145	92	92