Energy Quantization, Light, and the Electromagnetic Spectrum

SC.912.P.10.9 – ENERGY QUANTIZATION

SC.912.P.10.18 – ELECTROMAGNETIC SPECTRUM

• What was unique about Bohr’s model of the atom?• Discrete energy orbits

(or electron orbitals)

• Each orbital has an energy associated with it to prevent electrons from “wandering off”

• Orbital closest to nucleus = lowest energy• Electrons in “ground state”

• As orbitals get farther from nucleus they have increasing energy• Electrons in an “excited state”

Back to Niels Bohr & his atomic model

“The Original Double Slit Experiment”

https://youtu.be/Iuv6hY6zsd0

The Nature of Light

•Dual Nature • Particle AND wave

characteristics

Waves propagate… transports energy & momentum, NOT matter.

Quantization of Energy at the Atomic Level•Max Planck• Planck’s Constant: smallest amount of

energy that something can emit

• “h” = 6.626 x 10-34 J∙sec• “Energy is quantized”

• When energy is transferred, it can only be done so in discrete (whole “packets”) units of size hv(v = frequency)

• Quantum of Energy: ΔE=hv• Photon: the smallest possible quantity (or

quantum) of light. A “packet” of energy.

• Ephoton= hv = hc/λ• “c” = 3 x 108 m/s

(the speed of light!)

• Frequency (n): the number of waves that

pass a point in a given period of time

# of waves = # of cyclesUnits: hertz (Hz) or cycles/s = s−1

1 Hz = 1 s−1

• Wavelength (λ): the distance from one

crest to the next crest

The Electromagnetic Spectrum

v

λ

You MUST memorize the order of the energies!

Which of the following would be the best explanation of infrared waves?

A) They have lower frequencies than microwaves.B) They have shorter wavelengths than gamma waves.C) They have longer wavelengths than ultraviolet waves. D) They have higher frequencies than visible light waves.

SAMPLE TEST QUESTION:

This graphic will NOT be given to you, so it is

important to know the SPECIFIC ORDER of the

energies (gamma, xray, UV, vis, IR, microwave, radio)

Wavelength, Frequency, Energy…How are they related?

Frequency (v)

• Frequency and Energy?

• Frequency and Wavelength?

Wavelength (λ)

• Wavelength and Energy?

• Wavelength and Frequency?

v ↑ E↑

v↑ λ↓

λ↑ E↓

λ↑ v↓

Remember This!

• Frequency is DIRECTLY proportional to energy• Higher frequency (more waves per cycle) = higher

energy

• Frequency is INVERSELY proportional to wavelength• Higher frequency (more waves per cycles) = smaller

wavelength (less distance between each wave)

• Wavelength is INVERSELY proportional to energy• Higher energy = shorter wavelength

Spectra & Spectroscopy

• Each element has its own unique emission (atomic) spectrum• Like a fingerprint; characteristic• Pass light through sample of glowing hydrogen through a

prism it does not scatter into a continuous rainbow spectrum like white light

Emission spectrum for iron Emission spectrum for hydrogen