Light atomic spectra nuclear chemistry
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Light & Atomic Spectra & Nuclear Chemistry. Planck’s Constant. Types of Light. Visible light is the light that humans can see. Did you know?. Dogs can see only shades of gray and some insects can see light from the ultraviolet part of the spectrum. Seeing the Light.

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Light & Atomic Spectra & Nuclear Chemistry

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Light atomic spectra nuclear chemistry

Light & Atomic Spectra & Nuclear Chemistry

Planck’s Constant


Types of light

Types of Light

  • Visible light is the light that humans can see.


Did you know

Did you know?

  • Dogs can see only shades of gray

  • and some insects can see light from the ultraviolet part of the spectrum


Seeing the light

Seeing the Light

  • Visible light is the light that humans can see.

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

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


Light atomic spectra nuclear chemistry

Red

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


Electromagnetic radiation

electromagnetic radiation

  • Visible light is only one small portion of a family of waves called electromagnetic (EM) radiation.

  • EM waves includes radio waves, uv, infared, microwave, x-rays, gamma rays

  • Visible light is near the middle of the spectrum.


Roy g biv

ROY-G-BIV

  • ROY-G-BIV

  • represents all of the colors in the visible spectrum of light. R (red) - O (orange) - Y (yellow) - G (green) - B (blue) - I (indigo) - V (violet).

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

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


Prisms

Prisms

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

  • A prism is made up of two planar surfaces at an angle.

  • It uses the slower speed of light in glass to its advantage by refracting the light twice.

  • When the light ray leaves the prism, it speeds up again (entering the air) and refracts a second time.

  • That second dispersal creates the colorful spectrum of colors.


Light waves are classified by frequency of wavelength

Light waves are classified by frequency of wavelength

  • Low frequency= long wavelength

  • High frequency= short wavelength


Parts of a wave

Parts of a wave

  • Amplitude

  • height of the wave from normal to highest point.

  • Wavelength

  • the distance from origin to origin, crest to crest

  • Frequency

  • 1 wave per period

  • measured in Hz (1Hz = 1wave per second).


In 1900 max planck

In 1900, Max Planck

  • was working on the problem of how the radiation an object emits is related to its temperature.

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


The formula

The formula

  • The energy E contained in a photon, the smallest possible 'packet' of energy, is directly proportional to the frequency f :

  • Ephoton = hf

  • E = (6.626176 x 10-34J*s) * f (frequency)

  • and conversely:

  • F (frequency)= Ephoton / (6.626176 x 10-34J*s)

  • Frequency SI units are Hz or 1/s or s-1


Sample problem

Sample Problem

  • Example Problem: Calculate the energy in J of a quantum of radiant energy (the energy of a photon) with a frequency of 5.00 x 1015 Hz.

  • 1st list the knowns:

  • Frequency (f) = 5.00 x 1015Hz

  • h= 6.626 x 10-34 J*s (Planck’s constant)

  • Unknown: E


Light atomic spectra nuclear chemistry

  • Solve for the unknown:

  • E= h x f

  • E= (6.626 x 10-34 J*s) x (5.00 x 1015 1/s)

  • E=3.31 X 10-18J


Light atomic spectra nuclear chemistry

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


Light atomic spectra nuclear chemistry

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


Einstein

Einstein

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


Light atomic spectra nuclear chemistry

  • c=λf

  • c=speed of light = 3.0 x 108 m/s

  • λ= wavelength (make sure it is in meters (m) so the units will match)

  • f=frequency in Hz


Sample problem1

Sample Problem

  • Calculate the wavelength of the yellow light emitted by a sodium lamp if the frequency of the radiation is 5.10 x 1014 Hz

  • List the knowns:

  • Frequency (f) = 5.10 x 1014Hz

  • c=speed of light = 3.0 x 108m/s

  • Unknown: λ in m


Light atomic spectra nuclear chemistry

  • What is the wavelength of radiation with a frequency of 1.50 x 1013 Hz


Light atomic spectra nuclear chemistry

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


It s all energy

It's all Energy

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

  • Wavelength determines: energy & type of EM radiation

  • # of photons: states how much radiation is present


Photons determine how bright the light is

Photons determine how bright the light is….

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

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


Think of a dimmer switch

Think of a dimmer switch

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

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


Flame test lab

Flame Test Lab

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

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


So in the flame

So in the flame,

  • electrons get excited and pushed to higher energy levels

  • When they fall back down, they give off photons of light of different colors, based upon how far they fall.


For example a sodium na ion in an unexcited state has the structure 1s 2 2s 2 2p 6

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

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

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

For example, a sodium (na) ion in an unexcited state has the structure 1s22s22p6.


Light atomic spectra nuclear chemistry

It might fall straight back or jump through many levels…

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


Light atomic spectra nuclear chemistry

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

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

Sodium

Lithium

Copper Sulfate

Copper

Gas Flame

Potassium

Sodium Carbonate


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