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Waves
What do light waves have
to do with chemistry?
The Big Idea!
• The atoms of each element
have a unique arrangement of
electrons
Light and Quantized
Energy
• Light, a form of electromagnetic
radiation, has characteristics of
both a wave and a particle
Electromagnetic
Radiation
• Light is just one form of
electromagnetic radiation
• Electromagnetic radiation
travels in the form of waves
• All waves have amplitude,
wavelength, frequency and
speed
Electromagnetic Spectrum
US Frequency Allocations
Wavelength
•Symbol is λ
•Defined as the distance between two crests or
two troughs
Speed of Light
• Is it really a constant?
• It equals 3.00 x 108 m/s
• Symbol is c
Speed of Light
• The speed of light (3.00  108 m/s) is the
product of it’s wavelength and frequency
c = λν.
Frequency
• Its symbol is 
• The number of wave cycles that
pass a given point in one
second
• Measured in hertz (Hz)
(cycles/sec)
• C = λ
Frequency vs
Wavelength
• Long wavelengths have low
frequencies
• Short wavelengths have high
frequencies
Who is Max Planck and
why do we care?
• The year is 1895
• Physicist’s are trying to model
the EM radiation of a black body
• A black body absorbs all light
and emits it as black body
radiation
• Max is working hard to model
this
1895 – Viola!!
• Success!
• Devised Planck’s constant:
Equantum= h
E = amount of energy
h = Planck’s constant:
6.6262 x 10-34 J· s (J = joule)
What does this mean?
Matter can emit or
absorb energy
only in wholenumber
multiples of h :
1 h, 2 h, etc.
1905 – Einstein comes
on the scene
• Publishes a paper on light
quanta (Won Nobel Prize for this
in 1921)
• Explained photoelectric effect
using this particle based model
• Proved Planck’s model correct
• Millikan – Tried to disprove both
Planck and Einstein for 10 years
Einstein’s explanation of
his theory
• “According to the assumption
considered here, in the propagation of a
light ray emitted from a point source, the
energy is not distributed continuously
over ever-increasing volumes of space,
but consists of a finite number of energy
quanta localized at points of space that
move without dividing, and can be
absorbed or generated only as complete
units.”
1920’s - Louis de Broglie
• Scientist who used Planck’s
constant to predict that electrons
could act like waves, since waves
could act like particles
• This principle is used in electron
microscopes, where electrons
streams are diffracted the same way
light waves are diffracted by lenses
A picture taken with an
electon scanning
microscope
Photons
• Particles of light are called
photons
• Each photon carries with it a
specific value of energy based
on its frequency
• High frequency photons carry
large amounts of energy
Atomic Emission
Spectra
• Light in a neon sign is produced when
electricity is passed through a tube filled
with neon gas and excites the neon atoms.
• The excited atoms emit light to release
energy.
• When the light passes through a slit and
then a prism, a line spectrum is formed.
Line Spectra
Atomic Emission
Spectra
• A line spectrum is also called
an atomic emission spectrum
• It’s formed by the energy given
off, in the form of light, when an
electron moves from its excited
state to its ground state
• Origin of Spectral Lines
Atomic Emission
Spectra
• The atomic emission spectrum of an
element is the set of frequencies of the
electromagnetic waves emitted by the
atoms of the element when it is excited.
• Each element’s atomic emission spectrum is
unique.
Photograph of a line
spectrum from helium
Several examples
of line spectra
Quantum Theory and the
Atom
• Wavelike properties of electrons
help relate atomic emission
spectra, energy states of atoms,
and atomic orbitals
Bohr’s Model of the
Atom
• Bohr suggested that an electron moves
around the nucleus only in certain allowed
circular orbits.
Bohr’s Model of the
Atom
• When an electron drops from a higher
energy orbit to a lower-energy orbit, a
photon is emitted.
Electrons are Weird
• Heisenberg Uncertainty
Principle:
• It is impossible to know both the
location and velocity of an electron at
the same time
• An electron can only be located when
a photon strikes it. The collision
causes it to change direction and
velocity.
Heisenberg Uncertainty
Principle
How are electrons arranged
around an atom?
• Bohr determined that electrons
gained or lost energy in quanta, or
specific amounts. These he labeled
as quantum numbers, or n.
• The n numbers refer to the energy
levels, which are the same as the
period numbers on the periodic
table.
Energy sublevels are contained
within the principal energy
levels.
Energy levels can be thought of as rows of
seats in a theater. The rows that are higher up
and farther from the stage contain more seats.
What are sublevels?
• Each energy level is divided into
sublevels
• There are four different
sublevels: s, p, d and f
Probability and Orbitals
• Orbital: region around the
nucleus where an electron is
likely to be found
• Have characteristic shapes, sizes
and energies
• Each can only hold 2 electrons
with opposite spins
How do orbitals relate
to energy?
• Each principle energy level is
divided into sublevels: s,p,d,f
• Each sublevel has an odd number of
orbitals: s has 1, p has 3, d has 5,
and f has 7
What do the orbitals
look like?
Orbital in the s sublevel
Orbitals in the p sublevel
Orbitals in the d sublevel
Orbitals in the f sublevel
Each one of these orbitals
holds only two electrons.
The d sublevel holds 10
electrons total, and the f
sublevel holds 14 electrons
total.
Orbitals
Energy
Level
Sublevels
Orbitals
# of
Electrons
1
s
1
2
2
s
p
1
3
2
6
3
s
p
d
1
3
5
2
6
10
4
s
p
d
f
1
3
5
7
2
6
10
14
David's Whizzy Periodic Table
Electron Configuration
• A set of three rules can be used
to determine electron
arrangement in an atom
What is electron
configuration?
• Each electron has a characteristic
energy and a characteristic spin
• Each electron is located in a specific
orbital with a specific quantum
number; this is called its electron
configuration
• There are three rules to use to
determine where each electron is
located and what spin it has
What are the rules for
assigning configurations?
• Aufbau Principle: electrons are
added to an atom one at a time
starting with the lowest energy
orbital
• 1s will get the first 2 electrons (lowest
energy)
• 2s will get the second 2 electrons (next
higher energy)
• 2p will get the next 6 electrons (next
higher energy)
What are some
examples?
• Hydrogen: has 1 electron
• From the Periodic Table, it is in
row 1, so n = 1
• It has a 1s orbital
• Its configuration is 1s1
Another example
• Helium has 2 electrons
• According to the P. Table, it is
in the 1st row, so n = 1
• It has an s orbital
• Its configuration is 1s2
Another example
• Lithium has 3 electrons
• The first two electrons are the
same as in He, so the first term
is 1s2
• It is in the 2nd row, so n=2
• Its configuration is 1s2 2s1
What is sublevel
notation?
• The type of electron
configuration we have just done
is also called sublevel notation
• The order in which the levels fill
is shown on the next slide and
on your handout
You can tell which sublevel the
electrons of an element are in
by looking at the element’s location in the
Periodic Table.
S = pink
p = blue
d = green
f = yellow
What is the next rule for
assigning configurations?
• Pauli Exclusion Principle: Each
orbital can hold up to two electrons;
must have opposite spins
• Hund’s Rule: When electrons occupy
orbitals of equal energy, one
electron enters each orbital until all
the orbitals contain one electron
with spins that are parallel
What are electron
spins?
• Electrons have their own spins,
represented by up and down
arrows
• They can spin clockwise or
counterclockwise
• Each ortibal holds two
electrons, and they have to be
spinning in opposite directions
How do I represent this?
• Electron spins and the order in
which they fill orbitals can be
represented using an orbital
diagram
• Orbital diagrams use arrows
and lines or squares to
represent electrons in their
orbitals
What are some
examples?
• What is the orbital diagram for
boron?
• Its electron configuration is
1s22s22p1
• Its orbital diagram is
1s
2s
2p
Orbital Diagrams
Electronic
Configuration
The aufbau principle states that each electron occupies the
lowest energy orbital available.
What are valence
electrons?
• Electrons in the outermost energy
level (the n #)
• Can be determined by counting the
number of s- and p-electrons since
the most recent noble gas
• These electrons are primarily
responsible for the reactivities of the
elements in the s- and p-sections of
the Periodic Table
What are some
examples?
• How many valence electrons
does chlorine have?
• How many valence electrons
does sodium have?
• How many valence electrons
does aluminum have?