Light and Electrons!Light and Electrons!

Ch 11Ch 11

Light & Atomic SpectraLight & Atomic Spectra

A Brief Bit of History (development of the A Brief Bit of History (development of the quantum mechanical model of the atom)quantum mechanical model of the atom) Grew out of the study of lightGrew out of the study of light

By 1900, scientists accepted the idea that light was By 1900, scientists accepted the idea that light was made of waves. made of waves.

Light as WavesLight as Waves

Light consists of ELECTROMAGNETIC Light consists of ELECTROMAGNETIC RADIATION.RADIATION. Includes…Includes…

Radio wavesRadio wavesMicrowavesMicrowavesInfrared wavesInfrared wavesVisible lightVisible lightUltraviolet wavesUltraviolet wavesx- raysx- raysGamma raysGamma rays

Electromagnetic WavesElectromagnetic Waves

All waves travel at the speed of light (c)All waves travel at the speed of light (c) c = 3.00 c = 3.00 × 10× 1088 m /s m /s

Wave CharacteristicsWave Characteristics

Wave CharacteristicsWave Characteristics

Electromagnetic SpectrumElectromagnetic Spectrum

The Speed of Light EquationThe Speed of Light Equation

Speed of Light = wavelength Speed of Light = wavelength × frequency× frequency

c = c = λλ× × υυ

UnitsUnits Speed of light = c = 3.00 × 10Speed of light = c = 3.00 × 1088 m /s m /s Wavelength = Wavelength = λλ is in m is in m Frequency = Frequency = υυ is in Hertz (Hz) = cycles/ s is in Hertz (Hz) = cycles/ s

(1/s)(1/s)

Light as ParticlesLight as Particles

In the early 1900’s, German physicist Max In the early 1900’s, German physicist Max Planck was trying to understand why some Planck was trying to understand why some substances change color when heatedsubstances change color when heated

What Max thoughtWhat Max thought

As the substance is heated, its energy As the substance is heated, its energy changes in specific amounts of energy. It’s changes in specific amounts of energy. It’s not random.not random.

The amount of energy that can be emitted The amount of energy that can be emitted by a substance is directly proportional to by a substance is directly proportional to the frequency of the radiation given off.the frequency of the radiation given off.

Energy EquationEnergy Equation

Radiant Energy = Planck’s constant Radiant Energy = Planck’s constant × ×

frequencyfrequency

E = h × E = h × υυ

UnitsUnitsh = 6.626 × 10h = 6.626 × 10-34-34 J•s J•sE = Joules (J which is kg•mE = Joules (J which is kg•m22/s/s22) )

υυ = Hz (cycles/s or 1/s) = Hz (cycles/s or 1/s)

Energy & EinsteinEnergy & Einstein

The amount of energy given off by a photon is The amount of energy given off by a photon is directly proportional to the mass of that photondirectly proportional to the mass of that photon

E = mcE = mc22

E = radiant energy (unit – joules)E = radiant energy (unit – joules)

m = massm = massphotonphoton (unit – kg) (unit – kg)

c = speed of light (3.00 c = speed of light (3.00 × 10× 1088 m/s) m/s)

The Photoelectric Effect: Albert The Photoelectric Effect: Albert Einstein (1905)Einstein (1905)

So what does light have to do with So what does light have to do with chemistry?chemistry?

You can identify an element by the color of You can identify an element by the color of light it gives off when heated.light it gives off when heated.