Chapter
- 2
Structure of Atoms
EXERCISE
Multiple Choice Questions
Put a (✓) on the correct answer
1. Which
one of the following results in the discovery of proton:
(a)
Cathode rays
(b) Canal rays ✓
(c)
X-rays
(d)
Alpha rays
2. Which
one of the following is the most penetrating?
(a)
Protons
(b)
Electrons
(c)
Neutrons ✓
(d)
Alpha particles
3. The
concept of orbit was used by:
(a)
J.J Thomson
(b)
Rutherford
(c)
Bohr ✓
(d)
Planck
4. Which
one of the following shell consists of three subshells.
(a)
O
shell
(b)
N shell
(c)
L shell
(d)
M shell ✓
5. Which
radioisotope is used for diagnosis of tumor in the body?
(a)
Cobalt-60
(b)
Iodine-131 ✓
(c)
Strontium-90
(d)
Phosphorus-30
6. When
U-235 breaks up, it produces:
(a)
Electrons
(b)
Neutrons ✓
(c)
Protons
(d)
Nothing
7. The
p subshell has:
(a)
One orbital
(b)
Two orbitals
(c)
Three orbitals ✓
(d)
Four orbitals
8. Deuterium
is used to make:
(a)
Light water
(b)
Heavy water ✓
(c)
Soft water
(d)
Hard water
9. The
isotope C-12 is present in abundance of:
(a)
96.9 %
(b)
97.6 %
(c)
99.7 %
(d)
None of these ✓
10. Who discovered the proton:
(a)
Goldstein ✓
(b)
J.J Thomson
(c)
Neil Bohr
(d)
Rutherford Short
Short answer
questions.
1. What
is the nature of charge on cathode rays?
Ans.
The cathode rays deflected towards positive plate in
an electrical field showing that these rays are negatively charged.
2. Give
five characteristics of cathode rays.
Ans.
Characteristics of cathode rays:
i.
These rays travel in straight lines
perpendicular to the cathode surface.
ii.
They can cast a sharp shadow of an
opaque object if placed in their path.
iii. They are deflected towards positive
plate in an electric field showing that they are negatively charged.
iv.
They raise temperature of the body on
which they fall.
v.
J.J. Thomson discovered their
charge/mass (e/m) ratio.
vi.
Light is produced when these rays hit
the walls of the discharge tube.
vii. It was found that the same type of rays
were emitted no matter which gas and which cathode was used in the discharge
tube.
3. The
atomic symbol of a phosphorus ion is given as ^P3~
(a)
How
many protons, electrons and neutrons are there in the ion?
(b)
What
is the name of the ion?
(c)
Draw
the electronic configuration of the ion.
(d) Name the noble gas which has the
same electronic configuration as the phosphorus ion has.
Ans.(a)
Protons = 15
Electrons = 18
Neutrons = 16
(b)
Phosphorous ion
(c)
1s2, 2s2, 2p6,
3s2, 3p6
(d)
Argon
4. Differentiate
between shell and subshell with examples of each.
Ans.
|
Shell
|
Sub-shell
|
|
The fixed
circular orbit which is associated with a definite amount of energy is called
shell or energy level.
|
Each shell is
composed of one or more sub shells.
OR
The sub
division of a shell in an atom is called sub shell.
|
|
Examples:
K,
L, M, N etc. are considered as the shell or energy levels of any atom.
|
Examples:
s,
p, d and f are considered as the sub shells of a shell.
|
5. An
element has an atomic number 17. How many electrons are present in K, L and M
shells of the atom?
Ans. K
= 2
L = 8
M = 7
6. Write
down the electronic configuration of Al3+. How many electrons are
present in its outermost shell?
Ans.
Electronic configuration of Al3+ = 1s2,
2s2, 2p6.
8 electrons are present in its outermost shell.
7. Magnesium
has electronic configuration 2, 8, 2.
(a) How many electrons are in the outermost shell?
(b) In which subshell of the outermost
shell electrons are present?
(c) Why magnesium tends to lose
electrons?
Ans.
(a)
There are two electrons are present in
outermost shell.
(b)
In s-subshell of the outermost shell
electrons are present.
(c)
It has two valence electrons. It has
tendency to lose electrons to get noble gas configuration of Neon (2,8).
8. What
will be the nature of charge on an atom when it loses an electron or when it
gains an electron?
Ans.
When atom loses electron it will be positively
charged while atom gains electron it will become negatively charged.
9. For
what purpose U-235 is used?
Ans.
When U-235 is bombarded with slow moving neutrons,
the uranium nucleus breaks up to produce Ba-139 and Kr-94 and three neutrons.
U-235 is used to get large amount of energy which
can be used to drive the turbines to generate electricity.
10. A patient has goiter. How will it
be detected?
Ans.
The goiter in a patient can be detected by using
Iodine-131 isotope.
11. Give three properties of positive rays.
Ans. Properties
of positive rays:
i.
These rays travel in straight lines in a
direction opposite to the cathode rays.
ii.
Their deflection in electric and
magnetic field proved that these are positively charged.
iii.
The nature of canal rays depends upon
the nature of gas, present in the discharge tube.
iv.
These rays do not originate from the
anode. In fact these rays are produced when the cathode rays or electrons
collide with the residual gas molecules present in the discharge tube and
ionize them as follows:M + e- à
M+ + 2e-
v.
Mass of these particles was found equal
to that of a proton or simple multiple of it. The mass of a proton is 1840
times more than that of an electron.
12. What are the defects of
Rutherford’s atomic model?
Ans. Defects of
Rutherford’s atomic model:
i.
According to classical theory of
radiation, electrons being the charged particles should release or emit energy
continuously and they should ultimately fall into the nucleus.
ii.
If the electrons emit energy
continuously, they should form a continuous spectrum but in fact, line spectrum
was observed.
13. As long as electron remains in an
orbit, it does not emit or absorb energy. When does it emit or absorb energy?
Ans.
The energy is emitted or absorbed only when an
electron jumps from one orbit to another. When an electron jumps from lower
orbit to higher orbit, it absorbs energy and when it jumps back from higher
orbit to lower orbit it radiates energy.
