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Waves & Particles
Electromagnetic Radiation
Is a fancy term for LIGHT
Human eyes only detect a very small
range of colors, so we tend to not think of
the others as “light” but they definitely are.
LPChem:Wz:1415
Electromagnetic Radiation: Light
Is a type of energyPropagates as a wave
LPChem:Wz:1415
• Wavelength = l• (Greek lambda)• Measured in meters
• Frequency = n• (Greek nu)• Measured in 1/s or
Hertz (Hz)
Electromagnetic Spectrum:
LPChem:Wz:1415
The Electromagnetic
Spectrum(all the “colors” of light)ROYGBV
High EnergyLow Energy
Electromagnetic Radiation: Light
Wavelength and frequency are inversely proportional As wavelength increases, frequency decreases (and
vice versa.
LPChem:Wz:1415
c = nl n
c = the speed of light: 3.0 x 108 m/s• The speed of light is a constant.• 3.0 x 108 m/s will be the value of
“c” whenever you solve this equation.
Electromagnetic Radiation: Light
A certain Utah radio station broadcasts at 99.5 FMFM radio stations give their frequencies in megahertz 99.5 FM = 99.5 x 106 Hz = frequency ( )n What is the wavelength used by this radio station?
LPChem:Wz:1415
c = nl n 3.0 x108 m/s = n l
99.5 x 106 Hz1/s
3.0 x108 m/s99.5 x 106 1/s
= l = 3.02 mThe radio waves that 99.5 FM broadcasts on are 3 meters long.
Electromagnetic Radiation: Light
Frequency and ENERGY are directly proportional As frequency increases, the energy of the light
increases.
LPChem:Wz:1415
E = h n n• h = Planck’s Constant: 6.626 x 10-34 Jns
• This number will be the value of “h” whenever you solve this equation.
• E is energy (in Joules)• n is still frequency (in Hz or 1/s)
Electromagnetic Radiation: Light
What is the Energy of the light (radio) wave 99.5 FM broadcasts on?
LPChem:Wz:1415
E = h n nE = 6.626 x 10-34 Jns n 99.5 x 106 Hz1/s
E = 6.59 x 10-26 J• 99.5’s radio signal is carried by waves of light with an
energy of 6.59 x 10-26 J.• Why so little energy? That is the energy generated by
just ONE electron in ONE atom.
Energy in the Atom
Electrons in the atom are in different Energy Levels (n) Orbitals further from the
nucleus have higher energy Electrons can absorb light to
jump up to a higher energy level.
Electrons can emit light to jump down to a lower energy level.
LPChem:Wz:1415
Energy in the Atom
Electrons are most stable at the lowest available energy (ground state) and will always return to ground as soon as possible. Any level above ground state is
considered an “excited state” The electron is “excited” when
above ground state.
LPChem:Wz:1415
Energy in the Atom
An electron moves from n = 1 to n = 3 Energy must be absorbed
An electron moves from n = 2 to n = 1 Energy must be emitted
Energy is conserved in all these changes!
LPChem:Wz:1415
Each element gives off (and absorbs) a unique set of wavelengths.
These spectra are used as “fingerprints” to identify elements.
LPChem:Wz:1415