ATOMIC STRUCTURE

ENERGY LEVELSElectrons possess energies to counteract the nuclear pull

Energies not of any amounts , but quantized energies, (energy levels)

• ) ) ) ) ) ) )

1 2 3 4 5 6 7K L M N O P Q

nucleus

• ) ) ) ) ) ) )1 2 3 4 5 6 7K 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 ?

yesAre 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 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

Degenerated orbitals

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 and present at all higher energy levels

3. D orbital starts on the 3rd and at all higher energy levels

4. F orbital starts on the 4th and present at all higher 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 leveltype of orbital

electron

Ordering of energy levels 1<2<3<4….Ordering of orbitals s<p<d<f

Aufbau Building Up PrincipleElectrons 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 41 2

F9 s2 S2 p5

Px Py Pz1 1 12 2

) )) )3 41 2

F9 s2 S2 p5

Px Py Pz1 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 nucleusN= 1,2,3,4.,5,6,7,

Azimuthal Quantum Number (l)- describes the kind of orbital where the electron occupiesL= 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 electronS= +1/2 = clockwise direction -1/2=counterclockwise direction