CHEM-111General Chemistry

Unit Three (b)Electronic Structure of Atoms

byCHEMISTRY DEPARTMENT

The Electron Configurations of Elements

Electron cloud

Nucleus

The Way the Electrons are

Distributed Around the Nucleus of an Atom

ELECTRON CONFIGURATION IN SINGLE ATOM

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.

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)

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.

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

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 s2 p

3 s3 p

4 s 3 d4 p

5 s 4 d5 p

6 s 4 f5 d

6 p7 s 5 f n = 7

n = 6

n = 5

n = 4

n = 3

n = 2

n =1

E

N

E

R

G

Y

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

Orbital and its Shapes Shape of s-Orbital

Electron density is same regardless of direction

spherical shape

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

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.

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

Four orbital, dx2-y2, dxy, dyz, dxz, have same shape each with four lobes of electron density.

dx2-y2 dxydyz

dxz dz2

Five different orientation of d-Orbitals

The shape of dz2 is different

Li

1

1H

2

3

He

C6

12

4

7Be B C N O F Ne4 5 6 7 8 9 10

9 11 12 1614 19 20

Na Mg Al Si P S Cl Ar11 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 Kr19 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 Mt UunUuuUub 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 8038 39 4037 41 42 43 44 4645 47 48 49 50 51 52 53 54

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho ErTm Yb

Ac Th Pa U Np Pu AmCm 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

Firstshell

Hydrogen

1H Electronic Distribution of Elements of first three Periods

Helium

2He

SecondShell

Lithium

3LiBeryllium

4BeBoron

5BCarbon

6CNitrogen

7NOxygen

8OFluorine

9FNeon

10Ne

ThirdShell

Sodium

11NaMagnesim

12MgAluminum

13AlSilicon

14SiPhosphors

15PSulfur

16SChlorine

17ClArgon

18Ar

Periodic Table of Elements and Distribution of Electrons In Shells

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

How to write Electronic configuration of elements

An unoccupied orbital represented by a line with orbital name written under it

Hydrogen Helium

S1 2 S 2 px y2 p z2 p

1s2, 2s1

Lithium Beryllium

Orbital Notation

Li

Examples

1s2 2s2

Be

ELECTRON CONFIGURATION OF FIRST 18 ELEMENTS

Electron Configurations of 2nd Period Element

Showing Two Notations

Name Symbol 1s 2s 2p 2p 2p Electron configuration

Lithium3Li

- - - 1s22s1

Beryllium 4Be - - - 1s22s2

Boron 5B - - 1s22s22p1

Carbon 6C - 1s22s22p2

Nitrogen 7N 1s22s22p3

Oxygen 8O 1s22s22p4

Fluorine 9F 1s22s22p5

Neon 10Ne 1s22s22p6

Electron Configurations of 3rd Period Elements

Name Symbol 1s 2s 2p 3s 3p Nobel-gas notation

Sodium 11Na 2 2 6 1 - [Ne]3s1

Magnesium 12Mg 2 2 6 2 - [Ne]3s2

Aluminum 13Al 2 2 6 2 1 [Ne]3s23p1

Silicon 14Si 2 2 6 2 2 [Ne]3s23p2

Phosphorus 15P 2 2 6 2 3 [Ne]3s23p3

Sulfur 16S 2 2 6 2 4 [Ne]3s23p4

Chlorine 17Cl 2 2 6 2 5 [Ne]3s23p5

Argon 18Ar 2 2 6 2 6 [Ne]3s23p6

Exercise1. How many electrons are in shell 2 of the following

elements? a) sodium b) nitrogen c) sulphur d) helium e) chlorine2. 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 -

Exercise4.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

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M. C. Q:

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 = 3a) 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