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Students ScoreBooster Series Videos
WAEC, SSCE, GCE, JAMB (UTME),
NECO and NABTEB
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Chemistry
Atomic Structure cont’d
Presented by
A.A.S Lateef
(Feb., 2016)
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THE ELECTRON
• Learning objectives, at the end of this lecture,
students should
 be able to describe the four quantum
numbers
Be able to name and draw the shapes of the
four quantum numbers
Have insights into writing the electronic
configurations of the elements
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Structure of Atom
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Locating the Electron
• Locating the electrons now uses quantum mechanical model
of the atom
• It is a highly mathematical model
• It states that the position and the momentum of electrons can
be determined at the same time
• Scientists developed the concept of orbitals- the volume of
space where electrons are found, to describe the position of
electrons
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Four Quantum Numbers
• Scientists introduced four quantum numbers to
describe the characteristics of electrons and their
orbitals
• These are;
 Principal quantum number, n
 Angular momentum (or azimuthal) quantum
number, l
 Magnetic quantum number, m
 Spin quantum number, s
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Four Quantum Numbers
(cont’d)
Table 1.1 The four quantum numbers and their descriptions
Name
Symbol
Description
Allowed Values
Principal
n
Orbital energy
Positive integers
(1,2,3,….)
Angular momentum
l
Orbital shape
Integers from 0 to n-1
Magnetic
m
Orientation
Integers from –l to +l
Spin
s
Electron spin
+1/2 or -1/2
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Principal Quantum Number (n)
• This describes the average distance of orbitals from
the nucleus
• It also describes the energy of the electron in an
atom
• The higher the value of n, the higher the energy and
the larger the orbital
• It can only have positive integer i.e. n = 1,2,3,4,5,…
• The value of n can not be negative
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Angular momentum Quantum Number
(l)
•
•
•
•
•
•
This is also called Azimuthal quantum number
It describes the shape of the orbital.
The value is limited by the value of n
It can only have positive integer i.e. n = 0 to n-1
E.g. if n =2, l = 0 and 1
NB: value of l defines the shape of the orbital and n
defines the size
• Orbitals that have the same value of n but different l
values are called subshells- these are given letters for
easy recognition.
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Angular momentum Quantum Number
(l)
Table 1.2 Letter designation of the subshells
l value
Letter
0
s
1
P
2
d
3
f
4
g
NB: Complete shell specification is done by specifying the values of n and l e.g. 2s, 3p
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Magnetic Quantum Number (m)
• Orientation of the orbitals in space is described by
this quantum number
• The value of m depends on the value of l (m = -I to
+l)
• E.g. if l =1, m = -1, 0, +1
• This means that there are 3 different p-subshells for a
particular orbital. These subshells have the same
energy but different orientations in space.
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Spin Quantum Number (s)
• It describes the direction of spin of electron in a magnetic
field---- clockwise or anticlockwise
• Only two values are allowed which are +1/2 and -1/2
• NB: for each subshell, there can only be maximum of 2
electrons (one with +1/2 and the other with -1/2).
Table 1.3 Quantum Numbers for the first two energy levels
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In summary,
• There are four quantum numbers
• They are collectively used to specify the position and energy
of a shell as well as the shape of the orbitals
• There letters that are used to specify the orbitals are s, p, d, f
etc
n
l(0 to n-1)
m(-l ..0..+l)
Orbitals
allowed
s
1
0
0
s
+1/2, -1/2
2
0,1
-1, 0, +1
s, p
+1/2, -1/2
3
0, 1, 2
-2, -1, 0, +1, +2
s, p, d
+1/2, -1/2
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Exercises
1. Using the Table 1.1, determine the four quantum
numbers for an atom with energy levels n = 3 and 4,
then find the maximum number of electrons each of
the shells can contain.
2. Write the name of the shapes of s, p and d orbitals.
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Solution
1.
• For n =3,
• l = 0,1,2 (s, p, d)
• m = -2, -1, 0, 1, 2
•
•
•
•
•
2.
Maximum number of electron = 18 (i.e 2x 9subshells)
For n =4,
l = 0,1,2,3 (s, p, d, f)
m = -3, -2, -1, 0, 1, 2,3
Maximum number of electron = 32 (i.e 2x 16subshells)
s= spherical
p = dumb-bell
d = double dumb-bell
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Curriculum Vitae
Full name: Saheed Adewale, LATEEF
Email: [email protected]
Educational Background
Kwara State Polytechnic, Ilorin (2005-2007), [ND, Science
Technology].
Federal University of Technology, Minna (2008-2012), [B.Eng.
Chemical Engineering].
King Fahd University of Petroleum and Minerals, Saudi Arabia
(2014-2016), [MSc, Chemical Engineering].
Awards won
Best Polytechnic graduating student (Kwara Polytechnic, 2007).
Best Undergraduate Design Project (FUTMinna, 2012).
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