1. CHEM-111
General Chemistry
Unit Three (b)
Electronic Structure of Atoms
by
CHEMISTRY DEPARTMENT

2. The Electron Configurations of
Elements
Electron cloud
Nucleus
The Way the Electrons
are
Distributed Around the Nucleus of an Atom

3. ELECTRON CONFIGURATION IN SINGLE ATOM

4. Electrons exist in a number of cloud-like
shell or energy levels ,one inside the
other
• The first innermost shell (n=1) ,K shell, is only
small can hold one or two electrons .
• The second energy level (n=2) is called the
L Shell.
• The third energy level, M shell corresponds to
n=3.
• The fourth energy level, the N shell ,corresponds
to n=4 and so on.

5. Energy Levels and their Capacity of
Electrons
The maximum number of electrons in
each shell = 2n2
No. of shell Name of shell Max. no. of electrons
n = 1 K 2 x 12
= 2
n = 2 L 2 x 22
= 8
n =3 M 2 x 32
= 18
n = 4 N 2 x 42
= 32
(where n = number of shell)

6. Arrangement of Electrons in Energy
Levels
• Electrons are concentrated in certain region of
space, called orbital.
• Each shell contains different types and
numbers of orbital.
• Each orbital has different shape and energy.
• Each orbital contains a maximum of two
electrons.

7. Each shell contains different types and
numbers of orbital
Each orbital can have maximum of two electrons
Shell
Number
(n)
Shell
name
Name of Orbital in
shells
S p d f
Total no.
of electrons
in different shell
1 K 1 0 0 0 2
2 L 1 3 0 0 8
3
4
M
N
1 3 5 0
1 3 5 7
18
32

8. Sequence of Energy Levels for Atomic
Orbital
The sequence of energy-levels is important in
determining the arrangement of electrons in
an atom.
This diagram is
useful to
determine which
orbital in an
atom are
populated by
electrons
1 s
2 s
2 p
3 s
3 p
4 s 3 d
4 p
5 s
4 d
5 p
6 s 4 f
5 d
6 p
7 s 5 f n = 7
n = 6
n = 5
n = 4
n = 3
n = 2
n =1
E
N
E
R
G
Y

9. Each individual box
represents an orbit
An electron occupies the lowest energy
orbital
Sequence of Energy Levels for Atomic Orbital
and Aufbau Principal
E
N
E
R
G
Y

10. Orbital and its Shapes
Shape of s-Orbital
Electron density is same regardless of direction
spherical shape

11. Electron Density Distribution in the 1s, 2s and
3s Orbital of an Atom
The nodes in the 2s and 3s orbits are actually
empty spheres on which the electron density is
zero.
3s2s1s
1s 2s 3s
Node
Orientation of s orbital

12. The shape of p orbital
p orbital has 2 dumbbell-shaped lobes
2p
The electron density is concentrated in two
regions
that lie on opposite sides of the nucleus,
with their centers along a straight line that
passes
through the center of the atom.

13. Three different orientation (x,y,z) of p orbital
around the nucleus
z
y
x
z
y
x
z
y
x
px orbita py orbital pz orbital
Orientation of p orbital

14. Four orbital, dx2
-y2
, dxy, dyz, dxz, have same shape
each with four lobes of electron density.
dx2-y2 dxy
dyz
dxz dz2
Five different orientation of d-Orbitals
The shape of dz2
is different

15. Li
1
1
H
2
3
He
C
6
12
4
7
Be B C N O F Ne
4 5 6 7 8 9 10
9 11 12 1614 19 20
Na Mg Al Si P S Cl Ar
11 12 13 14 15 16 17 18
23 24 27 28 31 32 35.5 40
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
19 20 21 2223 24 25 26 27 28 29 35 3630 31 32 33 34
39 40 45 48 51 52 55 56
Rb Sr Y Zr NbMo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Ti Pb Bi Po At Rn
Fr Ra Lr Rf Db Sg Bh Hs MtUunUuuUub UutUuq Uuh
IA
IIBIIIB IVB VIBVB VIIB VIIIB IB
IIA IIIA IVA VA VIA VIIA
VIIIA
1
2
3
4
5
6
7
8459 59 63.5 65 70 73 75 79 80
38 39 4037 41 42 43 44 4645 47 48 49 50 51 52 53 54
La Ce Pr NdPm Sm Eu Gd Tb Dy Ho ErTm Yb
Ac Th Pa U Np PuAmCm Bk Cy EsFm Md No
55 56
57 58 59 60 61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
87
89
88
90 91 92 93 94 95 96 97 98 99 101100 102
103 104 105 106 107 108 109 110 111 112 113 114 116
85.5 88 89 91 93 96 (98) 101 103 106 108 112 115 119 122 131
133 137
128 127
175 178.5 181 184 186 190 192 195 197 201 204 207 209 (209) (210) (222)
(223) 226 (260) (261) (262) (263) (262) (265) (266) (269) (272) (277) (289) (289)
138 140 141 144 (145) 150 152 157 159 162.5 165 167 169 173
227 232 231 238 237 (244) (243) (247) (247) (251) (252) (257) (258) (259)
Elements are arranged
in increasing order of their
atomic number
Periodic Table of Elements

16. First
shell
Hydrogen
1
H Electronic Distribution of
Elements of first three Periods
Helium
2
He
Second
Shell
Lithium
3
Li
Beryllium
4
Be
Boron
5
B
Carbon
6
C
Nitrogen
7
N
Oxygen
8
O
Fluorine
9
F
Neon
10
Ne
Third
Shell
Sodium
11
Na
Magnesim
12
Mg
Aluminum
13
Al
Silicon
14
Si
Phosphors
15
P
Sulfur
16
S
Chlorine
17
Cl
Argon
18
Ar
Periodic Table of Elements and Distribution of
Electrons In Shells

17. Valence and Core Electrons
Valence electrons
Electrons located (in incompletely filled) outer shell,
(main energy level) which take part in chemical
reaction.
Core electrons
Electrons in shells below the outer shell are core
electrons.
Core electrons
Valence electrons

18. How to write Electronic configuration of
elements
An unoccupied orbital represented by a line
with orbital name written under it
Hydrogen Helium
S1 2S 2px y2p
z
2p
1s2,
2s1
Lithium Beryllium
Orbital Notation
Li
Examples
1s2
2s2
Be

19. ELECTRON CONFIGURATION OF FIRST 18 ELEMENTS
Electron Configurations of 2nd
Period Element
Showing Two Notations
Name Symbol 1s 2s 2p 2p 2p Electron configuration
Lithium
3
Li
- - - 1s2
2s1
Beryllium 4
Be - - - 1s2
2s2
Boron 5
B - - 1s2
2s2
2p1
Carbon 6
C - 1s2
2s2
2p2
Nitrogen 7
N 1s2
2s2
2p3
Oxygen 8
O 1s2
2s2
2p4
Fluorine 9
F 1s2
2s2
2p5
Neon 10
Ne 1s2
2s2
2p6

20. Electron Configurations of 3rd
Period
Elements
Name Symbol 1s 2s 2p 3s 3p Nobel-gas
notation
Sodium 11
Na 2 2 6 1 - [Ne]3s1
Magnesium 12
Mg 2 2 6 2 - [Ne]3s2
Aluminum 13
Al 2 2 6 2 1 [Ne]3s2
3p1
Silicon 14
Si 2 2 6 2 2 [Ne]3s2
3p2
Phosphorus 15
P 2 2 6 2 3 [Ne]3s2
3p3
Sulfur 16
S 2 2 6 2 4 [Ne]3s2
3p4
Chlorine 17
Cl 2 2 6 2 5 [Ne]3s2
3p5
Argon 18
Ar 2 2 6 2 6 [Ne]3s2
3p6

21. Exercise
1. How many electrons are in shell 2 of the following
elements?
a) sodium b) nitrogen c) sulphur
d) helium e) chlorine
2. Write the electron shell arrangement for each of the
following elements.
Example: sodium 2,8,1
a) carbon b) argon c) sulfur d) silicon.
3. Identify the elements that have the following electron shell
arrangement.
Energy Levels 1 2 3
a. 2 e -
1 e -
b. 2 e-
8 e -
2 e -
c. 1 e-
d. 2 e-
8 e-
7 e -

22. Exercise
4.Name two elements which would exhibit physical and
chemical behavior similar to chlorine.
5.What are the number of electrons in the outer energy level
and the group number for each of the following elements.?
a) Lithium b) silicon c) neon d) argon
1.The maximum number of electrons in d-orbital is:
a) 2 b) 6 c) 10 d) 14
2. The electronic configuration of C is:
a) 1s2 b) 1s2
, 2s1
c)1s2
, 2s2
, 2p2
12
6
M. C. Q:

23. 3. Indicate the sub shell having maximum 14 electrons:
a) S orbital b) p orbital c) d orbital d) f orbital
4. Indicate the shell with n = 3
a) K b) L c) M d) N
5.The maximum number of electrons in M-shell is:
a) 2 b) 8 c) 18 d) 32
6.The electrons of an atom are distributed ranging from
higher to lower energy levels:
a) True b) False