Atomic structure

ATOMIC STRUCTURE
ENERGY LEVELS
Electrons possess energies to
counteract the nuclear pull

Energies not of any amounts , but quantized energies,
(energy levels)
• ) ) ) ) ) ) )
1 2 3 4 5 6 7
K L M N O P Q
nucleus

• ) ) ) ) ) ) )
1 2 3 4 5 6 7
K L M N O P Q
Electrons tend to occupy energy level of low
energy state
Ordering of energy levels : 1< 2< 3< 4…..

• 2n2 = maximum number of electrons in an
energy level
How many e’s can be accomodated in an energy level ?

1
2
3
4
5
6
7
Energy level 2 (n)2 Maximum
number of e’s
2(1)2 2 2
2(2)2 8 8
2(3)2 1818
2(4)2 32 32
) ) ) )1 2 3 4

2n2 = maximum number of electrons in an
energy level

2) 8) 18) 32) 50) 72) 98)
• Example
• Kr 36 2) 8) 18) 8)
• An energy level can have less than the maximum number of e’s provided energy
levels before it of low energies are filled.
• Ca20 2) 8) 10)
Ca20 2) 8) 8) 2)
Why ?
Not probable
probable

• 2) 8) 18) 32) 50) 72) 98)
1 2 3 4 5 6 7 energy levels
Are the 2 e’s (as they spin) equal in
enrgies ?
yes
Are the 8 e’s (as they spin)
equal in energies ?
No

SUBLEVELS OF ENERGY
• Electrons are not only restricted to certain
energy levels, 1….7 but they are also restricted
to certain sublevels of energy called orbitals.
• Orbital – space or region in the atom where an
electron is probably located.

orbital
shape Spatial orientation
spin repulsion
has
Gives rise to
Generated orbitals/ types

Kinds Types Designation
s
Maximum
number of
e’s
s 1 s 2
p 3 Px Py Pz 6
d 5 D d d d
d
10
f 7 F f f f f
f f
14

Kinds of orbitals
Kinds Types Designations Maximum
number of
e’s
s 1 s 2
p 3 Px Py Pz 6
d 5 D d d d
d
10
f 7 F f f f f
f f
14

1. S orbital starts on the 1st
and present at all higher
energy levels
2. P orbital starts on the 2nd
energy levels
3. D orbital starts on the 3rd
and at all higher energy
levels
4. F orbital starts on the 4th
energy levels.
1 2 3 4 5 6 7
s S s s s s s
p p p p p p
d d d d d
f f f f
g g g
h h
i

Ordering of Orbitals s < p < d < f
• Ca 20 s2) s2 p6)s2p6) s2)

Properties of an Electron
E’E’
E’ E’
Spins around
Produces a magnetic field
whose polarity depends upon
the direction of the spin
Repel each other maximally
to become stable
Always
Thus as they spin in opposite direction,
opposite polarites of the magnetic fields
will attract the e’s together

ELECTRONIC CONFIGURATION
• Distribution of the electrons of a given atom into
their respective energy levels and orbitals.
n l
x
energy level
type of orbital
electron
Ordering of energy levels 1<2<3<4….
Ordering of orbitals s<p<d<f

Aufbau Building Up Principle
Electrons tend to occupy energy level and orbital of low energy states.
1 2 3 4 5 6 7
s S S s s s s
p P p p p p
d d d d
f f

• 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p
•

Pauli Exclusion Principle
• Two electrons can occupy a given orbital at
the same time provided they are of opposite
spins.
E’ E’

Hund’s Rule
• Degenerated orbitals (types of orbitals) within
the same energy level are of equal energies.
Electrons occupy them one at a time before
they would pair.
) )) )
3 4
1 2
F9 s2 S2 p5
Px Py Pz
1 1 12 2

) )) )
3 4
1 2
F9 s2 S2 p5
Px Py Pz
1 1 12 2

QUANTUM NUMBERS
• An electron of a given atom can be described by four quantum numbers
Principal Quantum Number (n)- describes the relative distance of the electron
from the nucleus
N= 1,2,3,4.,5,6,7,
Azimuthal Quantum Number (l)- describes the kind of orbital where the
electron occupies
L= 0…..(n-1)
Magnetic Quantum Number (m)= describes the type of orbital where the
electron is.
M= l (l-1) …0….(l-1) –l
Spin Quantum number (s)= describes the direction of the spin of an electron
S= +1/2 = clockwise direction -1/2=counterclockwise direction

Atomic structure

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