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.

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Electromagnetic Radiation: Light

Is a type of energyPropagates as a wave

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• Wavelength = l• (Greek lambda)• Measured in meters

• Frequency = n• (Greek nu)• Measured in 1/s or

Hertz (Hz)

Electromagnetic Spectrum:

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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.

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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?

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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.

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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?

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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.

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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.

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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!

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Each element gives off (and absorbs) a unique set of wavelengths.

These spectra are used as “fingerprints” to identify elements.

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