This post contains all the main and important topics which have complete and detailed solutions of Chapter 4 Structure of Atom. These solutions are based on the latest Rajasthan Board syllabus and prescribe NCERT book.
|
Board |
RBSE |
|
Subject |
Science |
|
Chapter |
Structure of Atom |
|
No. of Intext questions |
15 |
|
No. of End exercise questions |
19 |
|
Prescribed Book |
NCERT Science |
Structure of Atom Questions - Answers
Answers of Questions on Page 39
Q1. What are
canal rays?
Ans. These rays are positively charged
radiations which are called canal rays.
Q2. If an atom
contains one electron and one proton. Will it carry any charge or not?
Ans. The atom containing one electron and
one proton will not carry any charge and it is neutral because one positive
charge (Proton) balances one negative charge (electron)
Answers of Questions on Page 41
Q1. On the basis of Thomson’s
model of an atom. Explain how the atom is neutral as whole.
Ans.
According to Thomson’s atomic model – An atom consists of a positively charged
sphere and electrons are embedded in it. The positive charges and negative
charges are equal in magnitude so an atom is neutral.
Q2. On the basis of Rutherford’s
model of an atom, which subatomic particle is present in the nucleus of an
atom?
Ans.
Protons
Q3. Draw a sketch of Bhor’s model
of an atom with three shells.
Ans.
Q4. What do
you think would be the observation if the
Ans. If the
Answers of Questions on Page 41
Q.1 Name the three sub-atomic particles of an atom.
Ans. Electrons,
protons and neutrons.
Q.2 Helium atom has an atomic mass of 4 μ and two protons in
its nucleus. How many neutrons does it have?
Ans.
Atomic mass = Number of protons + Number of neutrons
4 = 2 + Number of
neutrons
Number of
neutrons = 4 -2 = 2
Answers of Questions on Page 42
Q.1 Write the distribution of electrons in carbon and sodium
atoms.
Ans.
|
For
Carbon |
|
Atomic
number = 6 |
|
Number
of protons = 6 |
|
Number
of protons = Number of electrons |
|
Electronic
distribution = K L
2 4 |
|
For
Sodium |
|
Atomic
number = 11 |
|
Number
of protons =6 |
|
Number
of protons = Number of electrons |
|
Electronic
distribution = K L
M
2 8 1 |
Q.2 If K and L shells of an atom are full, then what would be
the total number of electrons in the atom?
Ans.
K
shell can hold 2 electrons
While L shell can hold 8 electrons
When both the shells are full, there will
(8+2) = 10) electrons in the atom.
Answers of Questions on Page 44
Q1. How will you find the valency of chlorine, sulphur and
magnesium?
Ans.
Valency – The combining
capacity of an atom is known as valancy.
For
Chlorine
Atomic number =
17
Protons =17
Electrons = 17
Electrons distribution
= KLM
287
Chlorine needs 1
electron to complete its outermost shell, so its valency is -1 (accepts one
electron)
For
Sulphur
Atomic number =
16
Protons =16
Electrons = 16
Electrons distribution
= KLM
286
Sulphur needs 2 electron to complete its outermost
shell, so its valency is -2 (accepts two electron)
For
Magnesium
Atomic number =
12
Protons =12
Electrons = 12
Electrons distribution
= KLM
282
Magnesium donates
2 electrons to complete its outermost shell, so its valency is +2 (donates two
electron)
Answers of Questions on Page 44
Q.1 If the number of electrons in an atom is 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?
Ans.
|
Atomic
number = Number of Protons =8 |
|
Number
of electrons = number of protons , so atom will be neutral. There is no
charge on the atom |
Q.2 With the help of table given, find out the mass number of
oxygen and sulphur atom.
Table : Composition of Atoms of the First
Eighteen Elements with Electron Distribution in various Shells
Ans.
For Oxygen
Number of protons = 8
Number of neutrons= 8
Atomic number = 8
Mass
number = P + N = 8 + 8= 16
For Sulphur
Number of protons = 16
Number of neutrons= 16
Atomic number = 16
Mass
number = P + N = 16 + 16= 32
Answers of Questions on Page 45
Q.1 For the symbol H, D and T tabulate three sub-atomic
particles found in each of them.
Ans.
For H ( 1H1)
Atomic number =1
Mass number =1
Number of protons =1
Number of electrons =1
Number of neutrons = 1-1=0
For D ( 1H2)
Atomic number =1
Mass number =2
Number of protons =1
Number of electrons =1
Atomic number =1 Mass number =3 Number of protons = 1 Number of electrons= 1 Number of neutrons= 3-1=2 Q.2 Write the electronic configuration of any one pair of
isotopes and isobar. Answer Isotopes –
Isotopes are atoms having same atomic number but different mass numbers.
|
Answers of End Exercise Questions on Page 46-48
Q.1 Compare the properties of electrons, protons and neutrons.
Ans.
Comparison between properties of Electron, Proton and Neutron
Ans.
According to J.J. Thomson model of an atom, electrons are embedded all over in the positively charged sphere. But experiments show that protons are present only in the nucleus and electrons revolve around the nucleus
Q.3 What are the limitations of Rutherford’s model of the atom?
Ans.
According to Rutherford’s model of an atom, electrons revolve in a circular orbit around the nucleus. But such particle would undergo acceleration and radiate energy and ultimately would loss its energy and fall into the nucleus. Now the atoms would become unstable, but atoms are quite stable.
This was not explained through Rutherford’s model of atom.
Q.4 Describe Bohr’s model of the atom.
Ans.
Bohr’s model of an atom
1. An atom has nucleus in the center.
2. Electrons revolve in definite circular path of fixed energy around the nucleus.
3.The electron can change its shell or energy levels by absorbing or releasing energy.
4. Electron does not radiate energy while moving in discrete orbit.
Q.5 Compare all the proposed models of an silicon given in this chapter.
Ans.
Q6. Summaries the rules for writing of distribution of electrons in various shells for the first eighteen elements.
Ans.
Following are the rules for writing of distribution of electrons in various shells for the first eighteen elements are-
The maximum number of electrons present in a shell is given by the formula- 2n2 .
n = orbit number- 1 ,2,3 etc.
Maximum numbers of electrons present in a shell are-
K shell (n =1) = 2n2 = 2 ×11 = 2 electrons
L shell (n = 2) = 2n2 = 2× 22 = 8 electrons
M shell (n= 3) = 2n2 = 2 ×32 = 18 electrons
N shell (n =4) = 2n2 = 2 ×42 = 32 electrons
The maximum number of electrons that can be accommodated in the outermost orbit is 8.
Electrons are not accommodated in a given shell, unless the inner shells are filled in a step wise manner.
Q.7 Define valency by taking examples of silicon and oxygen.
Ans.
Valency – The combining capacity of an atom is called valency.
Silicon
Atomic number = 14
Number of electorns = 14
Electronic configuration = K,L,M
2,8,4
Its outermost shell has 4 electrons which it can share with other atoms to complete its orbit hence its valency is 4.
Oxygen
Atomic number = 8
Number of electorns = 8
Electronic configuration = K L
2 6
Its outermost shell has 6 electrons. It will gain 2 electrons to complete its octet. Hence its valency is -2
Q.8 Explain with examples (i) Atomic number (ii) Mass number (iii) Isotopes and (iv) Isobars.
Ans.
(i). Atomic number – the atomic number of an element is equal to the number of protons in the nucleus of its atom.eg.- carbon has 6 protons so its atomic number is – 6
(ii). Mass number – The mass number is equal to the number of protons and neutrons in its nucleus. It is denoted by ‘A’.. eg. – Carbon has 6 protons and 6 neutrons, so its mass number is 6 +6 = 12
(iii). Isotopes - Isotopes are atoms having same atomic number but different mass numbers. eg- 6C14 6C14
(iv) Isobars - Isobars are atoms having same mass number but different atomic number.eg- - 18Ar40 , 20Ca40
Q.9 Na+ has completely filled K and L shells. Explain.
Ans.
Atomic
number of sodium is 11 and its electronic configuration is 2, 8, 1. Sodium ion
(Na+) is formed by the loss of one electron from sodium atom.
Na → Na+
+ e-
2,8,1 2,8
KLM KL
K and L shells of sodium ion have 2 and 8 electrons respectively and are completely filled.
Q.10If bromine atom is available in the form of, say two
isotopes
Ans.
Percentage
of Br isotope with mass number 79 = 49.7
Percentage of Br isotope with mass number 81 = 50.3
The average atomic mass of bromine atoms = `\frac{49.7 ×79 +50.3×81}{100}`
=`\frac{392666.3 + 4074.3}{100}`
= `39.263 + 40.743 = 80.006u`
Q.11 The average atomic mass of a sample of an element X is
16.2 μ. What are percentages of isotope
Ans.
Let
the percentage of the isotope
Ans.
For
Z =3, the element is lithium (Li)
Electronic configuration of lithium
Z = 3 = K L
2 1
As the outermost shell has 1 electron. Its valency is 1.
Q.13 Compositions of the nuclei of two atomic species X and Y are given as under:
|
|
X Y |
|
Protons |
6 6 |
|
Neutrons
|
6 8 |
Give the mass number of X
and Y, what is the relation between the two species?
Ans.
Mass
number of
X
= 6 + 6 = 12
Y
= 6 + 8 = 14
Both X and Y contain equal number of protons but different number of neutrons. Hence, X and Y are isotopes.
Q.14 For the following statements write “T” for true and “F” for false:
(a) J. J. Thomson proposed that the nucleus of an
atom contain only nucleus.
(b) A neutron is formed by an electron and a proton combining
together. Therefore, it is neutron.
(c) The mass of an electron is about 1/2000 times
that a proton.
(d) Isotope of iodine is used for making tincture iodine, which is used
as a medicine.
Ans.
(a) False (b) False (c) True (d) False
Q.15 Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
(a)
Atomic nucleus (b) Electron (c) Proton (d) Neutron.
Ans. (a) Atomic nucleus.
Q.16Isotopes of an element have:
(a) The same
physical properties
(b) Different chemical
properties
(c) Different number of
neutrons
(d) Different atomic
numbers.
Ans. (c) Different number of neutrons.
Q.17 Number of valence electrons is Cl- ion are:
(a)
16 (b) 8 (c) 17 (d) 18
Ans.
As
the electronic configuration of chlorine Cl (Z = 17) is 
Q.18 Which one of the following is a correct configuration of sodium?
(a) 2, 8 (b) 8, 2, 1 (c) 2, 1, 8 (d)
2, 8, 1
Ans. (d) Atomic number of sodium = 11
Its electronic configuration
Q.19 Complete the following:
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