This chapter is from Module 2 Matter in Our Surroundings. This post provides you complete answer of all intext and terminal questions given in Chapter 5- Atomic Structure.
Our experienced teachers have provided
easy and accurate answers to all questions that will help you complete your
assignments. You can also solve the worksheet 5 on the basis of these solutions.
Atomic Structure - Overview
In this lesson on chemical reactions and
equations form NIOS class 10 Science, students will gain a basic understanding
of how chemical change occur and they will able to write and balance chemical
equations. This lesson also classifies chemical reactions into different types.
Intext Questions 5.1 with Answers
Q1. Name two charged particles which constitute all
matter.
Answer
All matters are
constituted of two charged particles-
1. Electrons
(negatively charged particle)
2. Proton
(positively charged particle)
Q2. Describe a cathode ray tube.
Answer
A cathode ray tube is a sealed glass tube from which
the air is removed. It has two electrodes- (i) cathode (negative) (ii) anode
(positive).
When a high voltage is passed through the electrodes,
a beam of negatively charged particles emits from cathode to anode. This beam
is called cathode rays.
Q3. Name the negatively charged particles emitted from
the cathode in the cathode ray tube?
Answer
Electron
Q4. Why do the canal rays obtained by using different
gases have different e/m values?
Answer
The canal rays are positively charged
particles (protons). These are formed from atoms of the gas present in the
tube. Different
gases consist of different types of atoms and the mass of positive ions is also
different. The e/m ratio depends on both the charge and mass of the particles.
So different gases produce canal rays with different e/m values.
Intext Questions 5.2 with Answers
Q1. Describe Thomson’s model of atom. What is it
called?
Answer
Thomson’s model of an atom is known as ‘Plum Pudding
Model’ or watermelon model. According to this model-
1.An atom is
a positively charged sphere in which negatively charged electrons are embedded
in it like seeds in watermelon or plum in pudding.
2.Electrons
do not move inside the atom.
Q2. What would have been observed in the α-ray scattering
experiment if the Thomson’s model was correct?
Answer
If the Thomson’s model was correct, then
1. The
alpha particles should have passed straight through the atom.
2. No significant deflection of alpha particles
would have been observed.
Q3. Who performed the α-ray scattering
experiment and what were the observation?
Answer
The alpha ray scattering experiment was performed
Geiger and Marsden.
Observations
1. Most of the
alpha particles passed straight through the gold foil.
2.A few
particles were deflected at small angles.
3.Very few
(about 1 in 20,000) were deflected back at angles greater than 90º almost
rebounded.
Q4. Describe the model of atom proposed by Rutherford.
Answer
1. An
atom contains a dense and positively charged region in the centre, it was
called as ‘nucleus’.
2. All
the positive charge of an atom and most of its mas was contained in the
nucleus.
3. The
size of the nucleus is very small compared to the size of the atom.
4. Most
of the atom is empty space.
5. Electrons
revolve around the nucleus in circular path called orbits.
Intext Questions 5.3 with Answers
Q1. Give any two drawbacks of Rutherford’s model of
atom.
Answer
These are the drawback of Rutherford’s model of atom-
1.An electron
revolving in a circular orbit around the nucleus should lose energy and
eventually fall into the nucleus. But this does not happen, so the model failed
to explain atomic stability.
2.This model
could not explain the distribution of electrons.
3.This model
could not explain the relationship between atomic mass and atomic number.
Q2. State the postulates of Bohr’s model.
Answer
The main postulates of Bohr’s model of the atom are-
1. Electrons
revolve around the nucleus in fixed circular orbits, called energy levels or
shells.
2. Electrons
do not radiate energy while moving in a particular orbit.
3. An electron
absorbs or emits energy when it jump from one energy level to another.
4. The energy
levels are denoted by integers n=1,2,3.. or letters K ,L,M,N…..
Q3. How does Bohr model of an atom explain the stability
of the atom?
Answer
Bohr explains electrons do not radiate energy when
revolving in a particular path. So, the atom remains stable.
Intext Questions 5.4 with Answers
Q1. What is a neutron and where is it located in the
atom?
Answer
A neutron is a subatomic particle located in the
nucleus of the atom.
Q2. How many neutrons are present in the α particle?
Answer
The α particle
contains two neutrons.
Q3. How will you distinguish between an electron and
proton?
Answer
|
Property |
Electron |
Proton |
|
Charge |
Negative |
Positive |
|
Mass |
Very small (1/1836 of mass
of proton) |
Relatively heavy |
|
Location in atom |
Revolve around the nucleus
|
Located in the nucleus |
|
Symbol |
e- |
P+ |
Intext Questions 5.5 with Answers
Q1. A sodium atom has an atomic number of 11 and mass number
23. Calculate the number of protons, electrons and neutrons in a sodium atom.
Answer
Given
Atomic number(Z)
=11
Mass number (A) =23
Solution
Number of protons = atomic number =11
Number of electrons = number of protons (in neutral atom)
=11
Number of neutrons = mass number – atomic number
=23-11=12
So,
Number of protons =11
Number of electrons =11
Number of
neutrons =23
Q2. What is the mass number of an atom which has 7 protons
and 8 neutrons?
Answer
Given
Protons = 7
Neutrons = 8
Solution
Mass number(A)= protons + neutrons = 7+8=15
So mass number =15
Q3. Calculate the number of electrons, protons and
neutrons in 
and 
.
Answer
Given
- Atomic number(Z)= 18 and Mass number(A) =40
Solution
Number of protons = atomic number = 18
Number of electrons = Number of protons=18
Number of neutrons = Mass number – atomic number =
40-18=22
So,
Number of protons = 18
Number of electrons =18
Number of neutrons= 22
Given
– Atomic number(Z)= 19 and Mass number(A)=40
Solution
Number of protons = atomic number = 19
Number of electrons = Number of protons=19
Number of neutrons = Mass number – atomic number = 40-19
=21
So,
Number of protons = 19
Number of electrons =19
Number of neutrons= 21
Intext Questions 5.6 with Answers
Q1. How many shells are occupied in the nitrogen (atomic
number =7) atom?
Answer
Atomic number of Nitrogen =7
Electronic configuration = 2,5
So, 2 electrons
in K shell and 5 electrons in L shell
Therefore, two shell are occupied in the nitrogen
atom.
Q2. Name the element which has completely filled first
shell.
Answer
Helium (He)
Q3. Write the electronic configuration of an element
having atomic number equal to 11.
Answer
Electronic configuration of an element having atomic
number 11 is 2,8,1
Terminal Exercise Questions with Answers
Q1. How did J.J. Thomson discover the electron?
Explain his “Plum pudding” model of the atom.
Answer
Discovery of electrons
J.J. Thomson
used a sealed glass tube with low pressure and two electrodes- cathode and
anode. When he applied high voltage to electrodes.
Rays were emitted
from the cathode and moved towards anode; these rays were called cathode rays.
Thomson
concluded that cathode rays are made up of negatively charged particles and he
named them, “electrons”.
Plum Pudding Model of the Atom
According this model:
1. An
atom is a positively charged sphere.
2. Negatively
charged electrons are embedded in the sphere like plums in a pudding of seeds
in a watermelon.
3. The
total positive and negative charges are equal so the atom is neutral.
Q2. What made Thomson conclude that all atoms must contain
electrons?
Answer
Thomson observed that cathode rays were made up of
electrons (negatively charged particles). He also observed that nature of
cathode rays was the same irrespective of the metal or the gas used in the
cathode ray tube. So, Thomson concluded that all atoms must contain electrons.
Q3. Identify the following subatomic particles:
(a) The
number of these in the nucleus is equal to the atomic number.
(b) The
particle that is not found in the nucleus.
(c) The
particle that has no electrical charge.
(d) The
particle that has a much lower mass than the other subatomic particles.
Answer
(a) Protons
(b) Electrons
(c) Neutrons
(d) Electrons
Q4. Which of the following are usually found in the nucleus
of an atom?
(a) Protons
and neutrons only
(b) Protons,
neutrons and electrons
(c) Neutrons
only
(d) Electrons
and neutrons only
Answer
(a) Protons
and neutrons only
Q5. Describe Ernest Rutherford’s experiment with alpha
particles and gold foil. How did this lead to the discovery of the nucleus?
Rutherford’s
α ray
scattering experiment
Rutherford and
his assistants performed an experiment in which they placed a thin gold foil(about
1000 atoms thick) surrounded by a screen coated with zinc sulphide. When α particles
were bombarded on the gold foil, they produced flashes of light.
On the basis of
this experiment, they observed –
1. Most alpha particles passed straight through
the gold foil without deflection.
2. Some
alpha particles deflected at small angles.
3. A very few (about 1in 12000 particles)
particles bounced back.
Discovery of Nucleus
The alpha Particles are positively charged particles and
very few alpha particles bounced back. On the basis of this observation
Rutherford concluded that-
1. An
atom contains a dense and positively charged region located at the Centre of an
atoms, it was called nucleus.
2. Most
of the mass is contained in the nucleus.
Q6. What does the atomic number tell us about an atom?
Answer
The atomic number of an atom tells us the number of protons
present in the nucleus of that atom.
Q7. What is the relationship between the numbers of
electrons and protons in an atom?
Answer
In a neutral atom, the number of electrons is equal to
the number of protons.
protons are positively charged and electrons are negatively
charged particles.
So, total positive charge must balance the total
negative charge in a neutral atom.
Q8. How did Neils Bohr revise Rutherford’ atomic
model?
Answer
Basically, Bohr revised instability of atom, a drawback
of Rutherford’s model.
1. Bohr
proposed that electrons revolve around the nucleus in specific circular orbits
called energy levels or shells.
2. Each
orbit or shell has a fixed energy so electrons in these orbits do not radiate
energy.
3. Electrons
absorb or emit energy when they jump between two energy levels.
So, electrons
do not fall into nucleus.
Answer
The electron does not radiate energy when moving in
particular orbit. These orbits are called stationary state.
Q10. What is a shell? How many electrons can be accommodated
in L -shell?
Answer
A shell is a fixed energy level around the nucleus of
an atom where electrons revolve. These shells are denoted by the letters K, L, M,
N…. Or numbers n= 1,2,3….
Numbers of electrons in L- shell
The L -shell is
the second shell (n=2)
2n2 = 2(2)2
2× 4= 8
The L-shell can hold maximum 8 electrons.
Q11. State the rules for writing the electronic
configuration of elements.
Answer
1. The shells or energy levels are represented by
K, L, M, N.. or N=1,2,3…..
2. Electrons
are distributed first in the low energy level then in the high level.
3. Maximum numbers of electrons in each shell
must follow 2n2 where ‘n’ is the number of shells
|
Shell |
Symbol |
N |
Max electrons (2n2) |
|
1st |
K |
1 |
2 |
|
2nd |
L |
2 |
8 |
|
3rd |
M |
3 |
18 |
|
4th |
N |
4 |
32 |
4. Electrons
are filled in a new shell only when the previous shell is completely filled.
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