Download continuous spectrum

Light and Quantized
Energy
Learning Objectives
• Compare the wave and particle nature of light.
• Contrast continuous electromagnetic spectra
and atomic emission spectra.
• Explain why atoms of a particular element
give off specific wavelengths of light when
their electrons are excited.
Light and Quantized Energy
• Light, a form of
electromagnetic
radiation, has
characteristics of both a
wave and a particle.
• Light exhibits wavelike
behavior as it travels
through space.
• Light exhibits particle like
behavior as it interacts
with matter.
The Wave Nature of Light
Visible light is a type of electromagnetic
radiation-a form of energy that exhibits wavelike
behavior as it travels through space.
Examples: microwaves, x-rays, radio waves
Characteristics of Waves
• The wavelength (represented by λ, the Greek letter
lambda) is the shortest distance between equivalent
points on a continuous wave.
• The frequency (represented by ν, the Greek letter nu) is
the number of waves that pass a given point per second.
• The amplitude of a wave is the wave’s height.
Characteristics of Waves
All electromagnetic waves, including visible
light, travel at the speed of light.
Electromagnetic Wave Relationship: c = λν
c = speed of light, a constant (3.00 x 108 m/s)
ν= frequency
λ = wavelength
Electromagnetic Spectrum
• The electromagnetic spectrum is the range of
all possible frequencies of electromagnetic
radiation.
Continuous Spectrum
• A continuous spectrum
is an emission spectrum
that exhibits all the
wavelengths or
frequencies of visible
light (violet to red).
The Particle Nature of Light
• Max Planck studied the light
emitted by heated objects.
• His conclusion: matter can
gain or lose energy only in
small, specific amounts
called quanta.
• A quantum is the minimum
amount of energy that can
be gained or lost by an
atom.
• A photon is a particle of
light with a particular
frequency.
The Particle Nature of Light
• A relationship between the energy of a quantum
and the frequency of the emitted radiation
• Relationship between energy and freqency E = hν
E = Energy,
h = Planck’s constant (6.626 x 10-34 Js)
ν = frequency,
The equation shows that the energy of radiation
and the radiation’s frequency are directly
proportional.
Light’s Dual Nature
• The energy of a photon of light is directly
proportional to its frequency.
– Energy ↑ Frequency ↑
– Energy ↓ Frequency ↓
• Energy and frequency are inversely proportional to
wavelength.
– energy/frequency ↑ Wavelength ↓
– energy/frequency ↓ Wavelength ↑
Long wavelength = low frequency = low energy
Short wavelength = high frequency = high energy
Learning Check
List the following in order of increasing
wavelength: microwaves, ultraviolet (UV),
gamma (γ), x-rays
Learning Check
• List the following in order of increasing
energy: microwaves, ultraviolet (UV), gamma
(γ), x-rays
Learning Check
• What color of visible light has the longest
wavelength?
Learning Check
• What color of visible light has the highest
energy?
Bohr Model
• Suggested that electrons
orbit the nucleus in fixed
energy levels (or shells)
• Electrons could jump
between levels, giving off
light we can see
Bohr’s Model of the Atom
• Electron transitions
involve jumps of
definite amounts of
energy.
• This produces bands of
light with definite
wavelengths.
Energy States of Atoms
• The lowest allowable
energy state of an atom
is called its ground
state.
• When an atom gains
energy, it is said to be in
an excited state.
• Various possibilities of
excited states create
characteristic spectral
emissions.
Atomic Emission Spectra
• The atomic emission
spectrum or line
spectrum of an element
is the set of frequencies
of the electromagnetic
waves emitted by atoms
of a specific element.
Continuous vs Line Spectrum
Atomic Emission Spectra
• Like a fingerprint, each
element’s atomic
emission spectrum is
unique and can be used
to identify an element
Summary
• All waves are defined by their wavelengths,
frequencies, amplitudes, and speeds.
• In a vacuum, all electromagnetic waves travel
at the speed of light.
• Electromagnetic radiation has both wave and
particle properties.
• Matter emits and absorbs energy in quanta.
• White light produces a continuous spectrum.
• An element’s emission spectrum consists of a
series of lines of individual colors.
AllWrite RoundRobin
• All team members look at notes on page 108
and think of one potential test question and
write it down on your white board.
• Starting with TM#____ take turns sharing the
question you came up with.
• Team agrees on questions to write down.
• All team members record questions.
• Repeat until there are 3-4 questions per page
of notes.
Summaries
• When your team has finished recording the
cue column questions, work on your
summaries.
Title page 112, Electromagnetic
Spectrum
• Cut out and glue the electromagnetic
spectrum to page 112.
Title page 113 Electromagnetic
Spectrum Questions
• Cut out and glue the Electromagnetic
Spectrum questions to page 113.
Flame Demo
• I am going to light five different metal salts on
fire.
• Record the names of each metal salt and your
observations for each in your science
notebook.
Title page 114 Flame Demo
Metal Salt
Flame Color
Write the following question under
your data table.
• Question: Why did we only see one color for
each metallic salt rather than the colors that
would be present in a line spectra for each
element?
• If you weren’t here the day of the demo, use
the slides to complete your data table and
then answer the question.
Flame Demo
LiCl – Lithium Chloride
SrCl2 – strontium chloride
Flame Demo
KCl – potassium chloride
CuCl2 – copper II chloride
Flame Demo
BaCl2 – barium chloride
Spectrometer
• A spectrometer (spectrop
hotometer, spectrograph
or spectroscope) is an
instrument used to
measure properties
of light over a specific
portion of the
electromagnetic
spectrum, typically used
in spectroscopic
analysis to identify
materials.