Electron Configuration
and Light as a Wave
I.
Arrangement of electrons in principle
energy levels.
A. What keeps an electron from crashing into
the nucleus?
1. Plank – proposed that there is a fundamental
restriction on the amount of energy that an
object emits or absorbs and he called these
pieces of energy quantum.
2. Electrons in an atom have their energies
restricted to certain energy levels.
Quantized property is a property that can
have only certain values, that is not all values
are allowed. The energy of these levels
increases as the distance between the
electron and the nucleus increases.
3. These energy levels are called electron shells
in this book and in others are called
principle energy levels and are designated
by whole numbers 1 - 7. Electron shell is the
region of space around the nucleus that
contains electrons that have approximately
the same energy and that spend most of their
time approximately the same distance from
the nucleus.
a) For an electron to go to a higher energy
level, it must absorb energy.
b) For an electron to go to a lower energy
level, it must emit energy.
c) The energy emitted is equal to the energy
difference of the two levels.
4. The maximum number of electrons in an
energy level is 2n2, where n = the principle
energy level (i.e. 1 – 7).
II. Arrangement of electrons in sub-levels.
A. Principle energy levels are divided into
sublevels.
1. These sub-levels are labeled s, p, d, and f.
2. The sublevels are broken up into orbitals. An
orbital is the region of space surrounding a
nucleus in which there is a high probability
of finding up to 2 electrons.
a. Electrons can be either spin-up or spindown. When an orbital is full it will
have one electron spin-up and one
electron spin-down.
3. Sublevels have a maximum number of
electrons that they can contain.
s sublevel = 2 electrons
= 1 orbital
p sublevel = 6 electrons
= 3 orbitals
d sublevel = 10 electrons
= 5 orbitals
f sublevel = 14 electrons
= 7 orbitals
B. Filling the sublevels.
1. Lowest energy sublevel is filled first.
Aufbau principle states that electrons
normally occupy electron sub-shells in an
atom in order of increasing energy.
1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<
4f<5d<6p<7s<5f<6d.
The principle number being smaller does not
mean that it fills first.
2. Each sublevel can only hold a limited
number of electrons.
3. Hund’s rule states that when electrons are
placed in a set of orbitals of equal energy, the
order of filling for the orbitals is such that
each orbital will be occupied by one electron
before any orbital receives a second electron.
This minimizes repulsion.
4. Fill each sublevel before proceeding to the
next until you run out of electrons.
5. You include valance and core electrons.
a. Valance electrons are the outermost
electrons. These have the largest
principle energy number. These are the
electrons that are used for bonding.
b. Core electrons are the inner electrons
that are generally not used for bonding.
III. Quantum numbers all atoms can be
characterized by their quantum numbers.
A.
HOMO highest occupied molecular
orbital. When you look at an atom the homo
can be used to classify the atom.
B.
Principle energy level of the homo
gives you the value for the n. Example
Carbon has 6 electrons. Its electron
configuration is 1s22s22p2 so n=2.
C.
Angular Momentum Quantum
Number (l) this has values where l= n-1.
For the example with Carbon n=2, so can be
equal to l=1 which corresponds to a “p”
orbital.
Value of l Orbital
l=0
s
l=1
p
l=2
d
l=3
f
D.
Magnetic Quantum number ml ml is
equal to a value from –l to +l.
Orbital Value of l Value of ml
Number of orbits
s
l=0
0
1
p
l=1 -1, 0, 1
3
d
l=2 -2,-1,0,1,2
5
f
l=3 -3, -2,-1,0,1,2,3
7
6. Pauli exclusion principle electrons can be
placed in an orbital either spin up or spin
down. This is the fourth quantum number
ms. It can be either( + ½ )or (– ½ ). When
filling orbitals the ( + ½ ) is added first and
then the (– ½ ) is added after all the other
orbitals of the same energy have been filled.
7. Example What is the electron
configuration of oxygen? 1s22s22p4
What is the quantum number
configuration of oxygen?
n l
ml
ms
2 1 -1
–½
IV. Magnetism is the phenomena by which
materials exert attractive or repulsive forces on
other materials.
1. Paramagnetic atom has an electron
arrangement containing one or more
unpaired electrons. Attracted to a
magnet.
2. When an atom has unpaired electrons the
electrons can be lined up when exposed to
a magnetic field.
3. Diamagnetic atom has all electrons
paired.
V. Structure of the atom
Protons and neutrons are located in the nucleus
A.
Electrons are located outside the
nucleus.
1. Electrons are outside the nucleus in
quantized orbitals.
2. This tells us
E = h
E = energy
H = plank’s constant
= 6.6262 x 10-34 Js
 = frequency (1/sec)
3.
Photoelectric Effect – this was
discovered when it was observed that
certain colors of light would cause
electrons to be emitted from metal. In
addition certain colors of light were
never able to cause the loss of electrons.
Einstein showed that certain colors of
light have different amounts of energy
and that it takes the right amount of
energy to release an electron. If the light
does not have enough energy the e- is
not released.
VI. Light
Light has a dual nature
1. Light can be thought of as a particle –
as something that has energy
2. Light can be thought of as a wave
where it travels through space as a
wave.
B.
When thinking of light as a wave we
have terms that we need to know.
1. Amplitude – height if the wave from
its origin to its peak.
2. Wavelength – the distance between
the crest of the wave.
3. Frequency – this tells us how fast the
wave oscillates up and down.
4. Speed – tells us how fast the wave
moves.
a. For light we know that is travels
3.00 x 108 m/s in a vacuum. This
is called the speed of light.
C.
Wavelength
Amplitude
D.
Calculating involving waves.
1. E = h
E = energy
2.  = c/
 = wavelength
 = frequency
c = speed of light
3. The radio station I listen to is 101.1 MHz.
What is the wavelength and the energy?
a.  = c/
= 3.00 x 108m x
sec
sec
1.011 x 108
 = frequency is in units of
1
M = 1 x 106
sec
 = 2.967m
E = h
E = (6.6262 x 10-34 J sec) x
h = Planck’s constant
 = frequency
(1.011 x 108)
sec
= 6.699 x 10-26 J
E. Frequency vs. Wavelength
high 
short
low 
long
There is an inverse relationship between frequency
and wavelength