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How atoms
What is Light?
• LIGHT is a form of energy
• Light can be considered as a bunch
of individual light “packets” called
• Each packet has its own set of
properties (wavelength, etc)
• A bunch of these packets traveling
together is like a ray of light.
Continuous Spectrum= all colors
There are no “blank spots” in the
Why continuous spectrum?
• A solid is heated…all of its
atoms/molecules and their parts
move really fast
• Energy is given off as the atoms
constantly vibrate.
• Photons of all colors can be emitted.
• All colors blend into “white light”
Brightline Spectrum
When only certain photons are observed,
it means that only light packets of a
particular type are being emitted!
• Each photon has a specific energy
• So only certain energy exchanges are
happening within the heated substance.
• So there must only be certain ways of
changing the energy in the substance!
• This can be explained by the movement of
• We know from middle school that atoms
have “layers” of electrons called energy
• Each energy level has electrons with a
certain amount of energy in them that
matches the level.
• When the electrons change levels, they
have to gain or lose energy to do so.
• Each time they lose energy, they emit a
bundle of energy.
• We see that bundle as a photon!
• Atoms only emit photons of
specific energies
• WHY??
All about…
• A form of energy!
• Travels in waves
• Wave properties are all related
• All light is part of the electromagnetic
spectrum (like energy from the sun)
Wave properties
• Speed
• Wavelength
• Frequency
• Energy
• Light travels at the speed of light (duh!)
• The speed of light = 2.998 x 108 m/s
• The symbol “c” stands for the speed of
– c = 2.998 x 108 m/s
• All light waves will have the same speed,
so speed is a constant
• A specific quantity of light
• Bohr said that when energy is added to
atoms, the electrons gain a “quantum” of
energy to move to a higher level.
• When electrons relax back to their normal
state, they emit a quantum of energy to go
back to the lowest level.
• Photon is just the name for a quantum of
• Electron Transition – when an electron
moves from one level to another
– When an electron transitions to a higher
energy level, a photon is absorbed.
– When an electron transitions to a lower energy
level, a photon is emitted.
• The emitted photon is just a “piece”
of light.
• It has a specific energy value, so it
has a specific wavelength, frequency
and color
• If you can measure the wavelength
of the photon, you can calculate its
Gas Discharge Tubes
• Another way to give energy to the
atom is using electricity
Gives a spectrum just like
that of a flame…
Figure 5.12 in your textbook
• This is why scientists can calculate
the energy values of the levels within
an atom even though they can’t see