CHEMISTRY
BOOKS - PEARSON IIT JEE
FOUNDATION
ATOMIC STRUCTURE
Example
1. Write different isotopes of oxygen , carbon
and chlorine.
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2. What was the basis for the propenol of
Dalton's atomic theory ?
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3. (i) What are A,B,C,D and E in the given
figure?
(ii) What is the purpose of C?
(iii) Explain the role , of D in the phenomenone
taking place in the discharge tube.
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4. An atom of element is represented as . Z C
A
. After the emission of a β -particle , another
element Y is formed. Represent Y with atomic
number and mass number.
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5. Calculate the specific charges (e/m) of the
following particles and then arrange the
particles in the asceding order of their specific
charges.
(a) Electron
(b) Proton
(c) α-particle.
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6. Calculate the mass of a charged particle in
CGS units if its charge is x coulomb and
specific charge is y coulomb/g.
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7. The isotopes of an element have mass
numbers, A, A + 1, A + 2 . The ratio of
abundance of these isotopes is 3: 2: 4.
Calcualte the average atomic mass of the
element.
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8. Following conclusions are drawn by
observing α -ray scattering experiment. Write
the respecitve observations based on which
these conclusions are drawn.
(i) Non-uniform distribution of positive charge.
(ii) Presence of positively -charged core or
nucleus.
(iii) Presence of large empty space in an atom.
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9. Thomson's Model OF Atom || Rutherford's
Model OF Atom
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10. The wavelength of particular radiation is
700 nm(1 nm − 10
−9
m) .Find its frequency
(v).
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11. An element has protons whose mass is
equal to 23, 881, times that of an electron.
Identify the element and write its electronic
configuration.
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12. Write the electronic configuration and the
atomic number of the atom which becomes
stable by gaining 3 electrons in fifth shell.
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13. What is ratio of the amount of energy
required to remove an electron from hydrogen
and H e ion ?
+
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14. Comple the following table :
Note: Core electrons are inner electrons which
exclude valence electorns.
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Very Shory Anser Type
1. Which postulate of Dalton's atomic theory is
considered to be correct even toady ?
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2. The value of the Plank's constant 'h' in erg -s
is ______.
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3. Why is Rutherford model called a nuclear
model ?
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4. Name the three fundamental particles in an
atom. Write the values of their mass numbers
and atomic numbers.
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5. The equation for the calcualtion of energy
of nth orbit if hydrogen atom derived by Bohr
is _____.
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6. Who discovered protons? Based on what
experiment was he able to discover these
protons ?
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7. Neutrons were discovered by bombarding
beryllium with _______ particles.
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8. What name did Max Planck give to energy
packages?
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9. What is Heisenberg's uncertainty principle ?
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10. Accroding to _______, the charges in an atom
are arranged like the pulp and seeds of a
watermelon.
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11. Which theory supported the particle nature
of an electron ?
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12. Give the value of Planck's constant in
(1) erg-s
(2) joule-s
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13. What happens when an electron jumps
from a lower energy level to a higher energy
level?
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14. What is an α -particles ?
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15. The circular paths in which electrons
revovle are called ________.
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16. In the formula E = hv, E is _______ and v is
_____________
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Short Answer Type
1. According to Rutherford's atomic model,
where are the protons and electrons located
in an atom ?
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2. The wavelength of particular radiation is
700 nm(1 nm − 10
−9
m) .Find its frequency
(v).
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Level 1 Concept Application
1. . 8 (O)
16
and . 8 (O)
18
are isotpes while
. 20 (Ca)
40
and . 18 (Ca)
40
are isobars.
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2. Energy is absorbed when the electron jumps
from K to L energy sheels.
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3. Anode rays are deflected towards the
negative plate in the presence of an electric
field because they consist of _________particles.
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4. Some of the α -rays deflect in acute and
obtuse angles due to the presence of the
________in the centre of the atom.
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5. The spectra produced by the deexcitation of
an electron is called______________.
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6.
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7. Which among the following pairs are having
different number of valence electrons ?
A. N a +
, Al
+3
B. P −3
, Ar
C. M g +2
, Ar
D. O −2 ¯
¯
, F
¯
Answer:
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8. Which among the following are isobars ?
A. . b
(X)
a
and . b (Y )
a
+ 1
B. . b
(X)
a
and . c (Y )
b
C. .
a a
b
(X) and . b + 1 (Y )
D. none
Answer:
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9. Which of these pairs has almost similar
masses ?
A. proton-electron
B. neutron-electron
C. electron. −1
(H )
1
D. nuetron . −1
(H )
1
Answer:
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10. The energy of an electron revolving in the
r
3 d orbit of Be +3
ion is __________ev
A. − 10.2
B. − 13.6
C. − 24.2
D. − 18.1
Answer:
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11. Which of the following concepts , was not
considered in Rutherford's atomic model ?
A. the electrical neutrality of atom
B. the quantisation of energy
C. electrons revolve around nucleus at very
high speeds
D. existence of nuclear forces of attraction
on the electrons.
Answer: B
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12. . 7 (X)
15
, . 7 (X)
11
are two naturally
occuring isotopes of an element X. what is the
percentage of each isotope of X if the average
atomic mass is 14 ?
A. 95,5
B. 80,20
C. 25,75
D. 16,84
Answer:
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13. A trinegative ion of an element has 8
electrons in its M shell. The atomic number of
the element is
A. 15
B. 18
C. 20
D. 16
Answer:
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14. Arrange the following statements given by
various scientists in chronological order :
A. 4 3 12
B. 42 31
C. 2431
D. 4321
Answer:
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15. What is the ratio of radii of the first
successive odd orbits of hydrogen atom?
A. 9 : 1
B. 1 : 9
C. 1 : 3
D. 3 : 1
Answer:
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16. An electron revolves round the nucleus in
the 3rd orbit and jumped to a higher orbit X
showing a difference in angular momentum
h
equal to . The value of 'X' could be.
π
A. 4
B. 6
C. 5
D. 7
Answer:
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17. Ruterford's α -particle scattering
experiment eventually led to the conclusion
that
A. mass and energy are related
B. the point of impact with matter can be
precisely determined
C. neutrons are buried deep in the nucleus
D. electrons are disturbed in a large speace
around the nucleus.
Answer:
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18. Arrange the following steps which are
carreid out in μ-ray experiment in the correct
sequence:
(i) Passage of μ- particles thorugh a slit.
(ii) bombardment of μ -partilces with a gold
foil
(iii) deflection of μ-particles
(iv) production of μ -particles
A. 4123
B. 4132
C. 1432
D. 1423
Answer:
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19. Which among the following pairs are
having different number of toatl electrons ?
A. N a +
and Al
+3
B. P −3
and Ar
C. M g +2
and Ar
D. O −2
and F
−
Answer:
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20. The postulates of Bohr's atomic model are
given below. Arrange them in the correct
sequence :
(1) As long the electron revolves in a particular
orbit, the electron does not lose its energy.
Therefore, these orbits are called stationary
orbits and the electrons are said to be in
stationary energy states.
(2) Electrons revolve round the nucleus in
specified circualr paths called orbits or shells.
(3) The energy associated with a certain
energy level increases with the increase of its
distance from the nucleus.
(4) An electron jumps form a lower energy
level to a higher energy level by absorbing
energy. But when it jumps from a higher to
lower energy level, energy is emitted in the
form of electromagnetic radiation.
(5) Each orbit or sheel is associated with a
definite amount of energy. Hence, these are
also called energy levels and are designated as
K,L,M and N, respectively.
A. 13452
B. 23514
C. 25314
D. 21435
Answer:
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21. The ratio of atomic number of two
elements A and B is 1: 2 The numebr of
electrons present in the valence sheel (3 r
d) of
A is equal to the difference in the number of
electrons present in the other two shells.
Steps involved for the calculation of ratio of
number of electrons present in a penultimate
sheel to anti-penultimate sheel of B are given
below :
Arrange them in the correct sequence :
(1) calculation of atomic number of B
(2) calcualtion of valence electrons present in
A.
(3) calacualtion of atomic number of A.
(4) calacualtion of number of electrons
present in the penultimate and anti-
penultimate shells of B.
(5) writing electronic configuration of B.
A. 23415
B. 23154
C. 45231
D. 42135
Answer:
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22. The equation given by Bohr to calculate
radius of n h orbit of hydrogen atom is
t
2 2
n h
A. r n
=
2
4π me
2 2
n h
B. r n
=
2
4π me
2
nh
C. r n
=
2
4π me
2 2
n h
D. r n
=
2 2
4π m e
Answer:
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23. The number of electrons present int the
valence shell of an atom with atomic number
38 is
A. 2
B. 10
C. 1
D. 8
Answer:
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24. The mass number of an atom whose
unipositive ion has 10 electrons and 12
neutrons is
A. 22
B. 23
C. 21
D. 20
Answer:
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Level 2 Concept Application
1. When the same isotopic gas is taken in two
discharge tubes, the angle of deflection is
found to be different though the strength of
the external electric field applied is the same.
Explain.
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2. In a canal ray experiment, different gases
were found to produce canal rays with the
same specific charge. Explain.
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3. Whne canal rays experiment is conducted
with hydrogen gas, scientists were found to
e
give particles with different values. Justify.
m
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4. Energy of the electron in the atom is
negative. Explain.
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5. Electronic spectra can distinbuish isobars
but not isotopes. Justify.
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6. If the energy difference between the orbits
when an electron in H atom excited to higher
energy orbit from its ground state is 12.1eV /
atom , calcualte the frequency of radiation
emitted (1eV = 1.602 × 10
− 19J
) when
electron comes back to second energy level.
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7. Is the energy difference between successive
orbits the same for all orbits? Justify your
answer.
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8. Though there is only one electron in a
hydrogen atom, the spectrum of hydrogne
contains a number of lines, How do you
explain this?
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9. What is the ratio of radius of the s
1 t orbit
to n
2 d orbit, if the velocity of the electron in
the 1 s
t orbit is twice that of the 2
n
d orbit.
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10. A particular atom has the 4th shell as its
valenced sheel. if the difference between the
number of electrons between K and N shells
and L and M shells is zero, find the atomic
number of the element and electronic
congfiguration of its stable ion.
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11. A stable unipositive ion of an element
contains three fully filled orbits.What is the
atomic number of the element ?
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12. Explain why a blackened plantinum strip
when placed the radius of curvature red hot,
only when the cathode taken has concave
shape.
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13. The average atimic mass of two isopoes
with mass numbers A and A + 2 is .
A + 0.25
Calculate the percentage abundance of the
isotopes.
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14. Spectral line given by an atom is a kind of
signature of the respective atom. Commnet of
this statement.
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15. Why was a spherical sulphide screen used
in α-ray scattering experiment ?
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16. Why is the source of α-particles kept inside
the lead block ?
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17. If Thomson's model is considered to be
correct, what would be the obervation of
Ruterford's α-ray scattering experiment?
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18. The ratio of the atomic numbers of two
elements A and B is 2: 3 A is an intery gas the
first 3 orbits completely filled. Identify A and B
and write their electronic configurations.
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19. A stable dipositive ion and a dinnegative
ion are isoelectrnic with an octet
configuaration in the second shell of their
atoms. Identify of the preceding and
succeeding elements and write their electronic
configurations.
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20. Predict the possible atomic number (s) of
an atom in which the third sheel is completely
filled and maximum 3 more electrons can be
added in that shell.
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21. The radius of n th
orbit of a single electron
species is 0.132n2
A
∘
. Identify the element.
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22. What is the frequency of light emitted
when an electron in a hydrogen atom jumps
from the 3 orbit to the 2
rd n
d orbit ?
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23. An electron having an angular momentum
of 1.05 × 10 − 34
joules jumps to another orbit
such that it has an angular momentum of
4.20 × 10
− 34
joules. Explain the possible
transitions.
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24. The mass number of a particular element
which has equal number of protons and
neutrons is 32. What is the electronic
configuration of the atom and its stable ion ?
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Level 3 Concept Application
1. In Millikan's oil drop experiment, the
distance between the metal plates, A and B to
which an electric potential is applied such that
A is positive and B is negative is 5 mm. An oil
drop is found to be suspended at a distance of
2 mm from B. Predict the change in the
position of the oil drop when there is a
sudden drop or rise in potential. Justify.
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2. Different gases in the discharge tube
produce different colours under suitable
conditions of pressure and voltage. Explain.
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3. Is the velocity of an electron in all orbits the
same for an atom of a particular element ?
How does it very for different single electron
specites ? Give reasons in support of your
answer.
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4. What is the ratio of distance between
successive orbits of 1 and 2 to 2 and 3 of
hydrogen atom ?
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5. If were to be used
y +1 y −1 +1
.x A or . B
x−1
instead of α -particles in Rutherford's
experiment, which would be better and why ?
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6. Draw a comparison between the potential
energy and kinetic energy of electrons in the
s
1 t orbits of hydrogen and He
+
ion. Also
comment on the total energy of the electrons
in the above cases.
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7. Though the kinetic energy of electrons
decreases with an increase in the distance
from the nucleus, the potential energy of the
electron increases. How do you account for
this ?
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8. Why is high voltage and low pressure
maintained in the discharge tube ?
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9. If canal ray experiments are conducted with
different isotopes of hydrogen gas, do the
canal rays produced show that same
deflection under the external eletric field? Give
reasons to support your answer.
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10.
if the given schematic diagrom represents,
Thomson's experiment and the corresponding
observation, what would be his atomic model
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