Light & Atomic Spectra & Light & Atomic Spectra & Nuclear ChemistryNuclear Chemistry

Planck’s ConstantPlanck’s Constant

Types of LightTypes of Light

Visible light is the light that humans can Visible light is the light that humans can see. see.

Did you know?Did you know?

Dogs can see only Dogs can see only shades of gray shades of gray

and some insects can and some insects can see light from the see light from the ultraviolet part of the ultraviolet part of the spectrumspectrum

Seeing the LightSeeing the Light

Visible light is the light that humans can Visible light is the light that humans can see.see.

More specifically, you see the light that is More specifically, you see the light that is not absorbed by objects. not absorbed by objects.

Green plants are green because they Green plants are green because they absorb all of the colors of the visible absorb all of the colors of the visible spectrum spectrum except except the green color (you the green color (you could also say the green wavelengths). could also say the green wavelengths).

RedRed

A red wall is red to your eyes because it is A red wall is red to your eyes because it is not absorbing light from the red not absorbing light from the red wavelengths.wavelengths.

electromagnetic radiationelectromagnetic radiation Visible light is only one small portion of a family Visible light is only one small portion of a family

of waves called electromagnetic (EM) radiation. of waves called electromagnetic (EM) radiation. EM waves includes radio waves, uv, infared, EM waves includes radio waves, uv, infared,

microwave, x-rays, gamma rays microwave, x-rays, gamma rays Visible light is near the middle of the spectrum. Visible light is near the middle of the spectrum.

ROY-G-BIVROY-G-BIV

ROY-G-BIV ROY-G-BIV represents all of the colors in the visible represents all of the colors in the visible

spectrum of light. R (red) - O (orange) - Y spectrum of light. R (red) - O (orange) - Y (yellow) - G (green) - B (blue) - I (indigo) - V (yellow) - G (green) - B (blue) - I (indigo) - V (violet). (violet).

Red has the longest wavelength and violet has Red has the longest wavelength and violet has the shortest. the shortest.

You could also say that red is the least energetic You could also say that red is the least energetic and violet is the most energetic of the visible and violet is the most energetic of the visible spectrum. spectrum.

PrismsPrisms

When refraction is at work in a prism it breaks the beam When refraction is at work in a prism it breaks the beam of visible light into its basic colors.of visible light into its basic colors.

A prism is made up of two planar surfaces at an angle. A prism is made up of two planar surfaces at an angle. It uses the slower speed of light in glass to its advantage It uses the slower speed of light in glass to its advantage

by refracting the light twice. by refracting the light twice. When the light ray leaves the prism, it speeds up again When the light ray leaves the prism, it speeds up again

(entering the air) and refracts a second time. (entering the air) and refracts a second time. That second dispersal creates the colorful spectrum of That second dispersal creates the colorful spectrum of

colors.colors.

Light waves are classified by Light waves are classified by frequency of wavelengthfrequency of wavelength

Low frequency= long wavelengthLow frequency= long wavelengthHigh frequency= short wavelengthHigh frequency= short wavelength

Parts of a waveParts of a wave

AmplitudeAmplitude height of the wave from normal to highest point. height of the wave from normal to highest point. WavelengthWavelength the distance from origin to origin, crest to crestthe distance from origin to origin, crest to crest FrequencyFrequency 1 wave per period 1 wave per period measured in Hz (1Hz = 1wave per second).measured in Hz (1Hz = 1wave per second).

In 1900, Max PlanckIn 1900, Max Planck was working on the was working on the

problem of how the problem of how the radiation an object radiation an object emits is related to its emits is related to its temperature. temperature.

Planck's constantPlanck's constant, , the constant of the constant of proportionality relating proportionality relating the energy of a the energy of a photon to its photon to its frequency; or frequency; or hh, and it , and it has the value has the value

The formulaThe formula

The energy The energy EE contained in a photon, the contained in a photon, the smallest possible 'packet' of energy, is smallest possible 'packet' of energy, is directly proportional to the frequency directly proportional to the frequency ff : :

EEphotonphoton = = hfhf EE = (6.626176 x 10 = (6.626176 x 10-34-34J*s) * J*s) * ff (frequency) (frequency)and conversely: and conversely: F F (frequency)(frequency) = = EEphotonphoton / (6.626176 x 10 / (6.626176 x 10-34-34J*s)J*s)Frequency SI units are Hz or 1/s or sFrequency SI units are Hz or 1/s or s-1-1

Sample ProblemSample Problem

Example Problem: Calculate the energy in Example Problem: Calculate the energy in J of a quantum of radiant energy (the J of a quantum of radiant energy (the energy of a photon) with a frequency of energy of a photon) with a frequency of 5.00 x 105.00 x 101515 Hz. Hz.

11stst list the knowns: list the knowns:Frequency (f) = 5.00 x 10Frequency (f) = 5.00 x 101515 Hz Hzh= 6.626 x 10h= 6.626 x 10-34-34 J*s (Planck’s constant) J*s (Planck’s constant)Unknown: EUnknown: E

Solve for the unknown:Solve for the unknown:E= h x fE= h x fE= (6.626 x 10E= (6.626 x 10-34-34 J*s) x (5.00 x 10 J*s) x (5.00 x 101515 1/s) 1/s) E=3.31 X 10E=3.31 X 10-18-18JJ

What is the energy of a photon of What is the energy of a photon of microwave radiation with a frequency of microwave radiation with a frequency of 3.20 x 103.20 x 10-11-11 Hz? Hz?

What is the energy of a photon of green light with a frequency of 5.80 x 1014 Hz?

EinsteinEinstein

Based on Planck's work, Einstein Based on Planck's work, Einstein proposed that light also delivers its energy proposed that light also delivers its energy in chunks; light would then consist of little in chunks; light would then consist of little particles, or particles, or quantaquanta, called , called photonsphotons, each , each with an energy of Planck's constant times with an energy of Planck's constant times its frequency. its frequency.

c=λfc=speed of light = 3.0 x 108 m/sλ= wavelength (make sure it is in meters

(m) so the units will match) f=frequency in Hz

Sample ProblemSample Problem

Calculate the wavelength of the yellow Calculate the wavelength of the yellow light emitted by a sodium lamp if the light emitted by a sodium lamp if the frequency of the radiation is 5.10 x 10frequency of the radiation is 5.10 x 101414 Hz Hz

List the knowns:List the knowns:Frequency (f) = 5.10 x 10Frequency (f) = 5.10 x 101414 Hz Hzc=speed of light = 3.0 x 10c=speed of light = 3.0 x 1088 m/s m/sUnknown: Unknown: λ in m

What is the wavelength of radiation with a What is the wavelength of radiation with a frequency of 1.50 x 10frequency of 1.50 x 101313 Hz Hz

What frequency is radiation with a What frequency is radiation with a wavelength of 5.00 x 10wavelength of 5.00 x 10-6-6 cm? cm?

It's all EnergyIt's all Energy

The quantum theory says light consists of The quantum theory says light consists of very small bundles of energy/particles very small bundles of energy/particles called photons.called photons.

Wavelength determines: energy & type of Wavelength determines: energy & type of EM radiation EM radiation

# of photons: states how much radiation is # of photons: states how much radiation is present present

Photons determine how bright the Photons determine how bright the light is….light is….

Lots of photons give a brighter, more Lots of photons give a brighter, more intense type of light. intense type of light.

Fewer photons give a very dim and less Fewer photons give a very dim and less intense light.intense light.

Think of a dimmer switchThink of a dimmer switch

When you use the dimmer switch on the When you use the dimmer switch on the wall, you are decreasing the number of wall, you are decreasing the number of photons sent from the light bulb. photons sent from the light bulb.

The type of light is the same while the The type of light is the same while the amount has changed. amount has changed.

Flame Test LabFlame Test Lab

Flame tests are used to identify the Flame tests are used to identify the presence of a relatively small number of presence of a relatively small number of metal ions in a compound. metal ions in a compound.

Flame colors are produced from the Flame colors are produced from the movement of the electrons in the metal movement of the electrons in the metal ions present in the compounds.ions present in the compounds.

So in the flame,So in the flame, electrons get excited and pushed to higher electrons get excited and pushed to higher

energy levels energy levels When they fall back down, they give off photons When they fall back down, they give off photons

of light of different colors, based upon how far of light of different colors, based upon how far they fall. they fall.

For example, a sodium (na) ion in an For example, a sodium (na) ion in an unexcited state has the structure 1sunexcited state has the structure 1s222s2s222p2p66..

When heated: electrons When heated: electrons gain energy and jump into gain energy and jump into any of the empty orbitals any of the empty orbitals at higher levels – at higher levels –

for example, into the 7s for example, into the 7s or 6p or 4d, depending on or 6p or 4d, depending on how much energy is how much energy is absorbed from the flame.absorbed from the flame.

Because the electrons Because the electrons are now at a higher and are now at a higher and more energetically more energetically unstable level, they tend unstable level, they tend to fall back down to to fall back down to where they were before where they were before

It might fall straight It might fall straight back or jump through back or jump through many levels…many levels…

Each of these jumps Each of these jumps involves a specific involves a specific amount of energy amount of energy being released as being released as light energy, and each light energy, and each corresponds to a corresponds to a particular color.particular color.

Whatever color is produced, tells you what Whatever color is produced, tells you what element you have.element you have.

This is a great way to determine an This is a great way to determine an unknown substance…unknown substance…