The document provides an overview of atomic structure, including the discovery and properties of positive rays, Planck's quantum theory, and quantum numbers that describe electron behavior in atoms. It outlines the shapes of orbital and distribution rules for electrons, including Aufbau's principle, Pauli’s exclusion principle, and Hund’s rule. Additionally, the document includes a series of multiple-choice questions to test understanding of these concepts.

1. CHEMISTRY
UNIT # 2
ATOMIC STRUCTURE
(REVIEW LECTURE)

2. • Discovery and Properties of Positive rays
• Planck’s Quantum Theory
• Quantum Numbers
• Shapes of s, p and d- Orbitals
• Rule for Electronic Distribution
• Electronic Configuration

3. PROPERTIES OF POSITIVE RAYS
 They are produced when electric current is passed
through gas at low pressure
 Have positive charge as deflected towards negative pole
of electric field
 Smaller em value than electron
 em value depends upon the gas filled in tube.
 Highest em value was obtained when H2 gas was filled.

4. Planck’s Quantum Theory
• Energy is emitted or absorbed only in terms of
wave packets in a discontinuous manner. These
wave packets are called quanta or photon.
• Energy of photon or quanta
E α v
E = h = hc/λ = hc
.
ѵ v

5. Quantum numbers: The Set of numbers that describe the complete
behavior of an electron in an atom [2,1,–1, +1/2]
Principle Quantum number: A non-zero, positive integer that describe the
number of shell size of atom and energy of electron in an atom. It is
denoted by ‘n’, n = 1, 2,3 …… also called as K, L, M and N shell
Azimuthal quantum number: it describe the number of sub shell in a shell
also describe the shapes of sub shell represented by ‘l’, l = n – 1
 n = 1  l = 0  s-subshell  sharp (spherical shape)
 n = 2  l = 1  p-subshell  principle (dumbbell shape)
 n = 3  l = 2  d-subshell  diffused (sausage shape)
 n = 4  l = 3  f-subshell  fundamental (complicated shape)
NOTE: Finely divided spectral lines seen by spectrometer in Bohr’s spectrum
give him about an other energy level that is explained by this quantum number

6. Magnetic quantum number: it is describe the number of orientation or
orbitals in a subshell. It is denoted by “m” ; m = l, m = –l, 0, +l
 l = 0 (s), m =  0 = 0  1- orbital  2 electrons
 l = 1 (p), m =  1 = -1 , 0 , +1  3- orbital  6 electrons
 l = 2 (d), m =  2 = -2, -1 , 0 , +1, +2  5- orbital  10 electrons
 l = 3 (f), m =  3= -3, -2, -1 , 0 , +1, +2, +3  7- orbital  14 electrons
 It explains the splitting of spectral lines in magnetic field

7. Shell (n) Sub-Shell (l) Orbital (m) No. of electrons
n = 1  K l = 0  s 1-orbital 2
n = 2  L
l = 0  s
l = 1  p
4-orbital 8
n = 3  M
l = 0  s
l = 1  p
l = 3 d
9-orbital 18
n = 4  N
l = 0  s
l = 1  p
l = 3 d
l = 4 f
16- orbital 32e
1
3




e
1
3
5





e
1
3
5
7







e

8. FORMULAE FOR SHELLS AND SUB-SHELLS
 No. of sub-shells in a shell = ‘n’
 No. of orbitals in a shell = ‘n2’
 No. of electrons in a shell = ‘2n2’
 No. of orbitals in a sub-shell = ‘(2l+1)’
 No. of electrons in a sub-shell = ‘2(2l+1)’

9. Shapes of orbital's
 s-orbital ------------Spherical
 p- orbital------------Dumb-bell
 d- orbital------------Complicated Double dumb-bell)

10. Auf Bau’s Principle
The electrons should be filled in energy sub-shells in
order of increasing energy values
Order of energy level of sub-shells
1s<2s<2p<3s<3p<4s<3d<4p
<5s<4d<5p<6s<4f<5d<6p<7s

11. Rules for Electronic configuration
 An orbital can occupy maximum two electrons
 Maximum no. of electrons in a shell can be calculated by
formula 2n2
n+l Rule:
 Electrons in a sub-shell are place in order of increasing
value of n+l rule
 For two same values of n+l electron is placed in that sub-
shell whose n value is lower

12. Hund’s Rule
If degenerated orbitals are available and more than one
electron is to be placed in them, they should be placed
in different orbitals with same spin rather than having
opposite spin in same orbital.

13. Pauli’s Exclusion Principle
It is impossible for two electrons residing in the same orbital of a poly-
electron atom to have same spin.
OR
It is impossible for two electrons residing in the same orbital of a poly-
electron atom to have same values of all four Quantum number

14. MCQ # 1
The lightest fundamental particle is
a. Electron
b. Proton
c. Neutron
d. All are equal

15. MCQ # 2
The mass of a proton is nearly the
same as that of
a. Hydrogen atom
b. Carbon atom
c. Oxygen atom
d. Nitrogen atom
Mass of proton in Kg
=1.6726 x 10-27
Same as that of hydrogen
atom

16. MCQ # 3
Electronic configuration of unknown
element M+2 = 2,8,18 the element is
a. Al
b. P
c. Zn
d. K

17. Which sub-shell has highest energy
A. n=5, l=3, m=+1
B. n=5, l=2, m=+2
C. n=4, l=3, m=0
D. n=4, l=0, m=+1
MCQ # 4

18. MCQ # 5
Number of electrons in the outermost
shell of Calcium ion (Ca+2) is
a. 20
b. 2
c. 8
d. 18

19. MCQ # 6
With increase in the value of principal
quantum number ‘n’, the shape of the p-
orbital’s remain same although their sizes
a. Decreases
b. Increases
c. Remains the same
d. May or may not
remain the same

20. MCQ # 7
Which shape is associated with orbital
designated by n=3 , l =2
a. Spherical
b. Dumb-bell
c. Double dumb-bell
d. none of the above

21. MCQ # 8
In electronic configuration of Cu and Cr
which of following is true for both
elements
A. 3d is full filled
B. 3d is half filled
C. 7 electrons in s-orbitals
D. 8 electrons in s-orbitals

22. Which rule is violated by any atom in its excited state
configuration
A) Auf Bau Principle
B) Pauli’s Exclusion Principle
C) Hund’s Rule
D) All of thes
MCQ # 9

23. Positive rays are produced
A. By burning of gas
B. By cooling of the gas
C. By the bombardment of cathode rays on gas
molecules
D. From anode like cathode rays, produced from
cathode
MCQ # 10