Light and the AtomLight and the Atom

LightLight Much of what we know about the atom has

been learned through experiments with light; thus, you need to know some fundamental concepts of light in order to understand the structure of the atom, especially the placement of the electrons.

Characteristics of Light– Has "Dual" nature (or split personality)– There are times in which it behaves like a WAVE

and other times when it behaves like a PARTICLE

Light as a WaveLight as a Wave

Electromagnetic SpectrumElectromagnetic Spectrum

Wave CalculationsWave Calculationscc = = λ λ

C = speed of light (constant 3 x 10C = speed of light (constant 3 x 1088 m/s) m/s)– νν = Greek letter nu, frequency = Greek letter nu, frequency– λλ = Greek letter lambda, wavelength = Greek letter lambda, wavelength

speed of electromagnetic waves is always speed of electromagnetic waves is always the same, wavelength and frequency can the same, wavelength and frequency can change and are inversely related change and are inversely related

frequencyfrequency – number of waves that pass a – number of waves that pass a given point per secondgiven point per second

WavelengthWavelength – the length of one entire – the length of one entire wavewave

exampleexample

The yellow light given off by a The yellow light given off by a sodium vapor lamp used for sodium vapor lamp used for parking lots has a wavelength of parking lots has a wavelength of 589 nm. What is the frequency of 589 nm. What is the frequency of this radiation? (pay attention to this radiation? (pay attention to the units)the units)

5.09 x 105.09 x 101414 s s-1-1

Light as a ParticleLight as a Particle

When light behaves as a particle, it is called a PHOTON.

We are interested in how much energy they have. The unit of energy we will use is the Joule, J.

Max Max Planck (1900)Planck (1900)

matter does not gain or lose energy in matter does not gain or lose energy in a continuous manner, but in small, a continuous manner, but in small, specific amounts (quanta) specific amounts (quanta)

quantum – minimum amount of energy quantum – minimum amount of energy that can be gained or lost by an atomthat can be gained or lost by an atom

mathematically demonstrated the mathematically demonstrated the relationship between energy of a relationship between energy of a quantum and emitted radiationquantum and emitted radiation

The Energy of LightThe Energy of Light

E = hE = hWhere Where

E = energyE = energy

h = h = Planck’s constantPlanck’s constant (6.626 x (6.626 x 1010-34-34Js)Js)

frequencyfrequency

ExamplesExamples

1. What is the energy of a photon of light whose frequency is 7.85 x 1015 Hz?

2. If a light has a wavelength of 550 nm, what is the energy of one photon of this light?