Structure Of The Atom Class 9 Science Exam Questions

Please refer to Structure Of The Atom Class 9 Science Exam Questions provided below. These questions and answers for Class 9 Science have been designed based on the past trend of questions and important topics in your class 9 Science books. You should go through all Class 9 Science Important Questions provided by our teachers which will help you to get more marks in upcoming exams.

Class 9 Science Exam Questions Structure Of The Atom

Class 9 Science students should read and understand the important questions and answers provided below for Structure Of The Atom which will help them to understand all important and difficult topics.

1 Marks Questions

Question. Number of valence electrons in Cl^– ion are:
(a) 16
(b) 8
(c) 17
(d) 18

Question. Which one of the following is a correct electronic configuration of sodium?
(a) 2,8
(b) 8,2,1
(c) 2,1,8
(d) 2,8,1.

Question. Atomic Number of an element is equal to:
(a) Number of Protons
(b) Number of electrons
(c) Number of neutrons
(d) Both a) and b)

Question. The charge of proton (p⁺) is:
(a) +16 x 10^-29C
(b) -16 x 10^-19C
(c) +16 x 10¹⁹C
(d) -16 x 10¹⁹C

Question. ²⁰₁₀Ne and ²²₁₀Ne are
(a) Isotopes
(b) Isobars
(c) Isotones
(d) Both a) and b)

Question. Helium (42He) has:
(a) 2P + and 2n^o
(b) 2P + and 4n^o
(c) 4P + and 2n^o
(d) 2P + and 4n^o

Question. What are canal rays?

Question. If an atom contains one electron and one proton, will it carry any charge or not?.

Question. Name the three sub-atomic particles of an atom.

For the following statements, write T for True and F for False.

Question. J.J. Thomson proposed that the nucleus of an atom contains only nucleons. 

Question. A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.

Question. The mass of an electron is about 12000 times that of proton.

Question. An isotope of iodine is used for making tincture iodine, which is used as a medicine. Put tick (ü) against correct choice and cross (×) against wrong choice in questions 15, 16 and 17 

2 Marks Questions

Question. On the basis of Thomson’s model of an atom, explain how the atomic neutral as a whole.
Answer. As per Thomson’s model of an atom, the number of electrons (negatively charged) are equal to the number of protons (positively charged) in an atom. Hence the + and – charges are neutralized by each other that makes atom neutral as a whole.

Question. On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?
Answer. The sub atomic particle proton is present in the nucleus of an atom according to Rutherford’s model of an atom.

Question. Draw a sketch of Bohr’s model of an atom with three shells.
Answer.

Question. What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?
Answer. Yes the observations would have been different if the α-particle scattering experiment is carried out using a foil of a metal other than gold.

Question. Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?
Answer. The number of neutrons present in a helium atom
= atomic mass – no. of protons
= 4-2 = 2

Question. Write the distribution of electrons in carbon and sodium atoms.
Answer. Distribution of electrons in carbon atom:
atomic number of carbon = 6 = 2,4
Distribution of electrons in sodium atom:
atomic number of sodium = 11 = 2,8,1

Question. If K and L shells of an atom are full, then what would be the total number of electrons in the atom?
Answer. If K and L shells of an atom are full, then the total number of electron in the atom will be 10 because K shell can accommodate total 2 and L shell can accommodate maximum 8 electrons that makes a total of 10.

Question. If number of electrons in an atomic 8 and number of protons is also 8, then
(i) what is the atomic number of the atom? and
(ii) what is the charge on the atom?
Answer. (i) atomic number = number of protons = number of electrons = 8
(ii) atom will be neutral (no charge) because number of protons (+) is equal to the number of electrons (-)

Question. With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.
Answer. mass number of oxygen = number of neutrons + number of protons
= 8+8 =16
mass number of sulphur = number of neutrons + number of protons
= 16 + 16 = 32

Question. What are the limitations of J.J. Thomson’s model of the atom?
Answer. Main limitation to the J.J. Thomson’s atomic model was that it didn’t explain the arrangement of electrons in an atom

Question. Na⁺ has completely filled K and L shells. Explain.
Answer. Na has atomic number 11, so its electronic configuration is = 2,8,1
When it gives away its outermost shell single electron it changes to Na+ =10= 2,8
The above configuration indicates completely filled K, L shells.

Question. If Z = 3, what would be the valency of the element? Also, name the element.
Answer. When Z = 3, so that element has 3 electrons in its shells distributed as = 2,1.
Its valency is 1 because it can easily give away its outermost single electron and the element is Lithium(Li).

3 Marks Questions

Question. Why metals are electropositive and non-metals are electronegative in nature?
Answer. Metals are electropositive in nature because all metals loose electrons from their outermost shell in order to become stable and hence become positively charged. Non-metals are electronegative in nature because all non-metals gain electrons in order to become stable and hence become negatively charged.

Question. Explain the formation of Al³⁺ ion and why is it formed?
Answer. Because Al has atomic number of 13, its electronic configuration is 2, 8, 3 so in order that it becomes stable, it should have 8 electrons in its lose 3e^– from its outermost shell and as result it has 8 e- in the outermost shell and forms Al³⁺ ion

Question. Find the percentage composition of sucrose (C₁₂H₂₂O₁₁).
Answer. The molecular mass of Sucrose (C₁₂H₂₂O₁₁) is
12 x (12) + 22 (1) + 11 (16)
= 144 + 22 + 176
= 342 g /mol.

The composition of sucrose by Mass is
C = 42.11%
H = 6.43%
O = 51.46%

Question. Complete the following Table:
Ion Number of electrons Atomic Number of Neutrons Atomic Mass
a) 16Rb⁺37
c) 24Mg²⁺ 12
c) 30Br^– 35
Answer. An element is represented as ^A_ZX
X – Symbol of element; Z=Atomic number A=Mass Number.
Z = Atomic Number = No. of protons
Number of protons = Number of electrons
A = Mass Number = No. of protons + No of neutrons.

Question. Calculate
a) The number of gram – atoms of oxygen
b) The number of atom of oxygen
c) The number of molecules of ozone in 32 g of ozone [O₃]
Answer. 1 Mole of O = Gram Atomic Mass = Number of atoms
a) In oxygen, 2 gram – 6.023 x 10²³ atoms are present
b) Gram Atomic mass of oxygen = atoms
= 1 Mole of oxygen
16g of oxygen (O) = 6.023 × 10²³
32g of oxygen (O₂) = 6.023 x 10²³ x 32 / 16
1.205 x 10²⁴
(c) 48 of O₃ = 6.023 x 10₂₃ molecules
1g of O₃ = 6.023 x 10²³ / 48
32g of O₃ = 6.23 x 10²³ / 48 x 48
= 4.015 x 10²³

Question. What mass of water will contain the same number of molecules as 8.0 g of ferrous oxide [FeO]?
Answer. Gram Atomic Mass = 6.023 x 10²³ atoms
So, 18 g of H₂O = 6.023 x 10²³ atoms.
In FeO = 56+16= 72 g
So, 72 g of FeO = 6.0²³ x 10²³/72
1g of FeO = 6.023 x 10²³ / 72
8g of FeO = 6.023 x 10²³ x 8 / 72
8g FeO = 0,669 x 10²³
18g of H₂O = 6.023 x 10²³ atoms
18 / 6.023 x 10²³ gms = 1 atoms
18 x 0,669 x 10²³ / 6.023 x 10²³ gm = 0,669 x 10²³ atoms
2g of water contains = 0,669 x 10²³
So, 2g of water will contain the same number of Molecules as 8 g of Feo.

5 Marks Questions

Question. How will you find the valency of chlorine, sulphur and magnesium?
Answer. The electrons present in the outermost shell of an atom are known as the valence electrons. Those electrons determine the valency of that atom.
The atomic number of chlorine is 17 = 2,8,7
so the number of valence electrons for chlorine is 7 and it needs 1 more electron to complete its octet (8). Therefore, its valency is one.
Similarly, sulphur = 16 = 2,8,6
so the number of valence electrons for sulphur is 6 and it needs 2 more electrons to complete its octet (8). Therefore its valency is two.
Similarly, for magnesium = 12 = 2,8,2
It becomes easier for magnesium to give away its two valence than to acquire 6 more therefore its valency is two.

Question. Describe Bohr’s model of the atom.
Answer. To remove the drawbacks of Rutherford’s atomic model and to explain structure of atom in detail Neils Bohr in 1912 proposed a model of atom. The special features of Bohr’s model are given below:
i) An electron revolves in the orbit of atom with well-defined energy.
ii) Energy of orbits increases from inner shell to the outer shells i.e. energy for orbit nearest the nucleus is lowest.
iii) If energy is supplied then electron moves from lower orbit ot the higher orbit and if an electron jumps from higher orbit (energy level) to the lower orbit (energy level) then energy is radiated as electromagnetic waves.
iv) Each orbit or shell represents an energy level. Such orbits are represented as K,L,M,N,O……….. and named from centre to outwards.
v) The shell or orbits are associated with certain amount of energy and energy of orbits/shells increases from inward to outwards.eg K<L<M<N<O…………

Question. Compare all the proposed models of an atom given in this chapter.
Answer. There are total three atomic models each of which tried to explain the atomic structure in a better way. Following table compares the specific characteristics of the models:

Question. Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.
Answer. The following rules are followed for writing the number of electrons in different energy levels or shells:
(i) The maximum number of electrons present in a shell is given by the formula 2n², where
‘n’ is the orbit number or energy level index, 1,2,3,…Hence the maximum number of electrons in different shells are as follows:
first orbit or K-shell will be = 2 x 1² = 2
second orbit or L-shell will be = 2 x 2³ = 8
third orbit or M-shell will be = 2 x 32 = 18
fourth orbit or N-shell will be = 2 x 42 = 32 and so on.
(ii) The maximum number of electrons that can be accommodated in the outermost or bit is 8.
(iii) Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in as tep-wise manner.

Question. Explain with examples
(i) Atomic number,
(ii) Mass number,
(iii) Isotopes and
(iv) Isobars.
Give any two uses of isotopes.
Answer. i) Atomic number = It is the number of protons present inside nucleus of the atom. It is represented as Z. Forge: for hydrogen Z= 1, because in hydrogen atom the number of protons is 1.
ii) Mass number = It is the total number of protons and neutrons present inside the nucleus of an atom and is represented by A = P + Nmass of carbon is 12 u because it has 6 protons and 6 neutrons, 6 u + 6 u = 12 u.
iii) Isotopes = They are atoms of the same element and have same atomic number but different mass number/atomic mass. for example: carbon,12 C and 14 6 C
iv) Isobars = They are atoms of different elements having same mass number but different atomic number. for example, calcium, atomic number 20, and argon, atomic number 18. The number of electrons in these atoms is different, but the mass number of both these elements is 40. That is, the total number of neutrons is the same in the atoms of this pair of elements.
third orbit or M-shell will be = 2 x 32 = 18
fourth orbit or N-shell will be = 2 x 42 = 32 and so on.
(ii) The maximum number of electrons that can be accommodated in the outermost or bit is 8.
(iii) Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in as tep-wise manner.

Question. Complete the following table.

Answer.

We hope you liked the above provided Structure Of The Atom Class 9 Science Exam Questions. If you have any further questions please put them in the comments section below so that our teachers can provide you an answer.