Chapter 2
Structure of atoms
Exercise Short Questions.
(1) What is the nature of charge on cathode rays?
The nature of charge on
cathode rays is negative.
(2) Give five characteristics of cathode rays.
Characteristics of cathode rays.
(a) They raise the temperature of the
object on which they fall.
(b)
They are deflected towards positive plate showing that
they are negatively charged
particles.
(c) When they strike the wall of the glass
tube ,they produce light.
(3) The atomic symbol of a phosphorus ion is
31P3-
15
(a)How
many protons, electrons and neutrons are there in the ion?
Number of protons = 15
Number of electrons =15+3=18
Number of neutrons =31-15
=16 neutrons
(b)What
is name of the ion?
As P has received three electrons and becomes anion also
known as phosphide ion.
(c)Draw
the electronic configuration of the ion?
1s2,2s2,2p6,3s2,3p6.
(d)Name
the noble gas which has the same electronic configuration as the phosphorus ion
has.
Argon has
the same electronic configuration as the phosphorus ion has.
(4)
Differentiate between shell and subshell with example of each.
Sr. No
|
Shell
|
Subshell
|
1
|
Shell is the main or principal energy
level.
|
Each shell is divided into sub energy
levels which are known as subshells.
|
2
|
Example : K-shell, L-shell, M-shell,
etc.
|
Example : s-subshell,
d-subshell,f-subshell, etc.
|
(5) An element has an atomic number 17. How many electrons
are present in K, L and
M shell of the atom?
Atomic number = 17
Electron = 17
Electrons in K shell = 2
Electrons in L shell = 8
Electrons in M shell = 7
Electronic configuration in subshells :
1s2, 2s2 ,2p6, 3s2, 3p5.
(6) Write down the electronic configuration of Al3+
. How many electrons are present in its outermost shell?
Atomic number = 13
Electrons in Al3+ = 13
Electrons in K shell = 2
Electrons in L shell = 8
8 electrons are present in the outermost shell of Al3+.
Electronic configuration in subshell :
1s2, 2s2, 2p6
(7) Magnesium has electronic configuration 2, 8 ,2.
(a) How many electrons are in the outermost shell ?
1s2, 2s2,2p6, 3s2
Electrons in the outermost shell = 2
(b) In which subshell of the outermost shell electrons are
present?
The outermost
electrons are present in 3s subshell.
(c) Why magnesium tends
to lose electrons?
All elements wanted to have the electronic configuration of
noble gases .So, they can complete their valence shell.
That’s why magnesium lose 2 electrons and become a noble gas
like neon (Ne).
(8) What will be nature
of charge on an atom when it loses an electron or when it gains an electron?
When an atom loses an electron, it will be called as cation
and its charge becomes positive. And when an atom gains electron, its carge
becomes negative and it will be called as anion.
(9) For what purpose U-235 is
used?
U-235 is used to get a large amount of energy by
controlled nuclear fission process in
nuclear reactors. This energy is used in boilers to convert water into steam.
The steam is used to generate electricity.
(10) A patient has
goiter. How will it be treated ?
Iodine-131 is used to detect the goiter in thyroid gland.
(11) Give three
properties of positive rays.
I.
They travel in a straight line opposite to the
direction of cathode rays.
II.
The nature of these rays depends upon the nature of
gas present in discharge tube.
III.
They show deflection in electric and magnetic field
that shows they are positively charged particle.
(12) What are the
defects of Rutherford’s atomic model?
· According to the
classical theory of radiation, electrons being charged particles should emit
energy continuously and ultimately fall down into the nucleus.
· 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?
Electron emit energy when it jumps from higher to lower orbit
and absorb energy when it jumps from lower to higher orbit.
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