Properties of Light
Electromagenetic
Spectrum
Electromagnetic Spectrum
-the range containing all of the possible
frequencies and wavelengths of
electromagnetic radiation
Types of
electromagnetic
radiation
Electromagnetic Spectrum
In order of increasing wavelength: Gamma Rays, XRays, Ultraviolet Rays, Visible Rays, Infrared,
Microwaves, Radio Waves
-Visible Light:
• the light WE can see
Properties of Light
-Wave description of Light
- light exhibits wavelike behavior as it travels through
space.
-
-
-
Wavelength (λ): distance between two peaks; unit of
measure – meter, cm, nanometer
Frequency (f): number of waves that pass a given point in a
specific time; unit of measure – Hertz (Hz)
Speed of light (c ): c= λf
c=3.00 X 108 m/s
Properties of Light
-
Particle description of light:
-
light can be thought of as being composed of
particles (Planck)
-
Photon: particle of light. Has zero mass and a
quantum of energy (Einstein)
-
Quantum: minimum quantity of energy that can be
lost or gained by an atom
Photoelectric effect
-
Photoelectric effect- refers to the emission of
electrons from a metal when a light of sufficient
energy shines on the metal
-
Wave theory of light couldn’t explain this effect
E = hf
E - energy in Joules of a quantum of energy
h - Planck’s constant = 6.626 x 10-34 J·s
f - frequency
Problems
1. Calculate the wavelength if the frequency of
radiation is 5.10 x 1014 Hz.
Problems
2. Find the energy in a quantum of light that has a
frequency of 1.7 x 1014 Hz
Problems
3. Find the wavelength of a photon of light with
an energy of 3.26 x 10-19 J.
Violet
Indigo
Blue
Green
Yellow
Orange
Red
400-424 nm
425-454 nm
455-489 nm
490-574 nm
575-579 nm
580-649 nm
650-700 nm
Find the color of a photon of light if it is known
to have an energy of 4.75x10-19J.
Properties of Light
Therefore, light has dual wave- particle properties
- It behaves like a wave AND a particle
H atom Line-Emission Spectra




When you pass a current through a gas at low
pressure, the energy of some of the gas atoms
increases.
Ground State - lowest energy state for an
electron.
Excited state - An electron that has a higher
potential energy
When an electron drops down from an
excited state to its ground state, light of a
certain wavelength is emitted
The Two Different Sides of the Spectrum
Screen
Prism
Slit
White light
source



CONTINUOUS SPECTRUM
FROM WHITE LIGHT SOURCE
VARIOUS COLORS BLENDED
TOGETHER
Gas discharge
tube



DISCONTINUOUS SPECTRA
FROM EXCITED ATOMS
DISTINCT SEPARATED, ONLY A
FEW COLORS
2
If an electron in the n = 1 level of an H
atom absorbs enough energy to move
to the n = 4 level. How much energy
is absorbed?
n
4
3
If an electron in the n = 4 level of an H
moves to the n = 2 level. How much
energy is emitted?
Light of what wavelength is emitted in
a transition from n = 4 to n = 2?
Energy
2
1
“Neon Lights”
Electron
-Is a particle & also has wave properties
-Bohr’s Model of Atom:
-Electrons circle around
nucleus in allowed paths (orbits)
-Electrons placed in different
orbits based on energy levels of the electron
-One electron can not be in two orbits at once and can
not be between orbits
*** Bohr’s model still has shortcomings… we will
discuss later)
Take Home Message
-Science is CONSTANTLY changing
-New research may disprove old findings
-New models and thoughts may be created as a
result
Review
1) Name the two properties that light has.
2) What is the type of light that we can see called?
3) Visible light is found on the _________ spectrum.
4) A particle of light that has zero mass and a quantum of energy is
called a ________.
5) The distance between two peaks is called_____
6) Name the model of an atom that said electrons circle around nucleus in
allowed paths based on energy level.
7) The number of waves that pass a given point in a specific time is
called ________
8) The minimum quantity of energy that can be lost or gained by an
atom is a____________.
9) The ______________ refers to the emission of electrons from a
metal when a light of sufficient energy shines on the metal
Quantum Numbers
Review
1) Name the two properties that light has.
2) A particle of light that has zero mass and a quantum of energy
is called a ________.
3) The minimum quantity of energy that can be lost or gained by
an atom is a____________.
4) Name the model of an atom that said electrons circle around
nucleus in allowed paths based on energy level.
Electron
-Is a particle & also has wave properties
-Bohr’s Model of Atom:
-Electrons circle around
nucleus in allowed paths (orbits)
-Electrons placed in different
orbits based on energy levels of the electron
-One electron can not be in two orbits at once and can
not be between orbits
*** Bohr’s model still has shortcomings… we will
discuss later)
Electrons as Waves
Early 20th century:
-De Broglie: believed electrons have dual waveparticle properties
-Scientists demonstrated that electrons could be
bent or diffracted
-Diffraction: bending of a wave as it passes by the
edge of an object
Electron “Detection”
-
Electrons are detected with interaction with
photons
Photons can knock an electron off its course
-
Heisenberg Uncertainty Principle:
-
-
It is impossible to determine simultaneously both
the position and velocity of an electron or any other
particle
Quantum Model
- Schrödinger: wave equation
- Quantum Theory:
-
-
Electrons can exist in atoms only at specific energy
levels
Wave equations only tell us probability of finding
electron in certain position
Currently it is believed:
-
Electrons do not travel in orbits, but orbitals
Orbital: 3-D region around nucleus. Indicates
probable location of finding an electron
Quantum numbers
-
Quantum numbers: specify the properties of
atomic orbitals and the electrons in orbitals
-
Four different Quantum Numbers
-
-
Principal Quantum Number
Angular Momentum Quantum Number
Magnetic Quantum Number
Spin Quantum Number
Principal Quantum Number
- Symbol: n
- Main energy level occupied by the electron
-
Whole numbers (1, 2, 3, …)
- n=1 : Lowest energy level (closest to nucleus)
- Gives an indication of the size of the orbital
Angular Momentum Quantum
Number
- Symbol: l
- Indicates the shape (sublevels) of the orbital
- l= zero, one, two,…. (n-1)
- Shapes s: spherical, p: dumbbell, d, f
Value of l:
Letter used:
0
s
1
p
2
d
3
f
Magnetic Quantum Number
- Symbol: m
- Indicates the orientation of an orbital in space
- s orbital has 1 orientation, p orbital has 3, d
orbital has 5, f has 7
Spin Quantum Number
- Indicates the spin of an electron in an orbital
- A single orbital can hold a maximum of 2
electrons with OPPOSITE spins
-
Practice:
-
-
How many orbitals are in n=3?
How many electrons are in n=3?
Electron Configuration
Objectives
-List the total number of electrons needed to fully
occupy each main energy level
-State the Aufbau principle, Pauli exclusion
principle, and Hund’s Rule
-Draw the electron configuration and orbital
notation to show the location of electrons in an
atom.
Electron Configuration
- Electron configuration: the arrangement of
electrons in an atom
- Rules for electron filling of orbitals:
-
-
-
Aufbau Principle: e- will occupy the lowest energy
level orbital available
Pauli Exclusion Principle: no two e- in the same
orbital can have the same spin
Hund’s Rule: orbitals of equal energy will fill
singularly before a second e- can occupy the same
orbital
The Order of Electron Filling
7s7p
6s6p
5s5p
4s4p
3s3p
2s2p
1s
7d
6d
5d
4d
3d
7f
6f
5f
4f
Remember the
Aufbau Principle
The Order of Electron Filling
7s7p
6s6p
5s5p
4s4p
3s3p
2s2p
1s
7d
6d
5d
4d
3d
7f
6f
5f
4f
Remember the
Aufbau Principle
Electron Configuration
-
-
Electron configuration shows the energy level
number, the orbital sublevel, and the number of
electrons in each orbital
# of e- are represented by a superscript
e- config for carbon
-
-
1s22s22p2
Write the e-config for fluorine.
Write the e-config for silver.
Orbital Notation
Orbital notation for Carbon
Orbital Notation
- Orbital notation shows e- in their orbitals
- First write the electron configuration
_____
_____ This is the orbital notation for Lithium
1s 2s
Remember the Pauli Exclusion Principle &
Hund’s Rule
Orbital Notation
-Draw the orbital notation for fluorine
-Draw the orbital notation for nitrogen
Review
-
-
-
What rule says orbitals of equal energy will fill
singly before a second e- can occupy the same
orbital
What rule says that e- will occupy the lowest
energy level orbital available
What rule says that no two e- in the same orbital
can have the same spin
Chapter 4-3
The Order of Electron Filling
7s7p
6s6p
5s5p
4s4p
3s3p
2s2p
1s
7d
6d
5d
4d
3d
7f
6f
5f
4f
Remember the
Aufbau Principle
Objectives
-
-
Write the noble-gas notation of a given element
Determine the element given the electron
configuration or orbital notation.
Determine the highest energy level that is
occupied and the last orbital that is filled of a
given element.
Noble Gases
-
Gases like helium, neon, and argon
Where are these on the periodic table?
-
-
-
Group 18
The outer shell (main energy level) is completely
filled with 8 electrons
We can use their electron configuration to help
abbreviate the e- config. of other elements
Noble Gas Configuration
-
The electron configuration of Manganese is:
-
-
-
Manganese is in period 4…. Look at the noble
gas in the previous period (period 3)--- Argon
Argon’s e- config. is:
-
-
1s22s22p63s23p64s23d5
1s22s22p63s23p6
We can shorten the e- config of Mn by writing:
-
[Ar] 4s23d5
Practice
- Write the Noble Gas Configuration of Na, Sr,
and P
Short cuts with the Periodic Table

Look at the period number, group number, and
block
Identify the following elements
A)
B)
C)
D)
1s22s22p63s23p3
[Ar]4s1
1s22s22p1
[Ne]3s2
Review
-
What is the last orbital occupied by an electron
in the elements:
-
-
He
Al
What is the highest energy level occupied by the
following elements:
-
Ca
Be