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
- an ion
- an isotope.
- an isobar
- another element.
Ans ; an isotope
3. The term nucleons refer to
- Protons and electrons
- only Neutrons
- electrons and neutrons
- Protons and neutrons
Ans ; Protons and neutrons
4. The number of protons, neutrons and electrons present respectively in
- 80, 80, 35
- 35, 55, 80
- 35, 35, 80
- 35, 45, 35
Ans ; 35, 45, 35
5. The correct electronic configuration of potassium is
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
|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
|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|
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.
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.
|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
|Total number of electrons||= K + L +M|
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