Physics and the Quantum

Mechanical Model Notes

Light and the Atomic Spectrum

• Light is composed of waves at different wavelengths

• The wave is composed of:– Wavelength (λ): is the distance between the crests– Frequency (ν): the number of wave cycles to pass a

point per time– Amplitude: The height of the crest from the origin

Waves

You can calculate the frequency and wavelength of light using the equation

c= λν

c = speed of light (3.0 x 1010 cm/s or 3.0 x 108 m/s)

λ = wavelength (cm or m – distance between crests)

ν = frequency (1/s or s-1 = hertz = Hz)

Electromagnetic Spectrum• Visible Light is composed of a small section of

the Electromagnetic Spectrum

• EMS- a scale of all forms of radiation that exhibit wave-like behavior as they travel through space

• Light can be broken up into a spectrum of colors (ROY G BIV)

red – orange - yellow – green – blue – indigo- violet Violet is the highest energy (shortest wavelength)

Red is the lowest energy (longest wavelength)

Electromagnetic Spectrum (EMS)

Types of Spectra

Types of Spectra

• Continuous: Produced by a hot, opaque (dense gas or solid). A RAINBOW of colors

• Emission/Dark Line: Produced by a hot, transparent gas

• Absorption: Produced by a cool, transparent gas

Atomic Emission Spectrum• Each element has its own unique emission

spectrum when it is excited

• Excitation is usually induced via heat, electricity, etc.

• Excited = move up an energy level (absorb a “quanta” of energy. When e moves back to ground state, a quanta of energy (called a PHOTON is released

Quanta = “Packet” of Energy

• Photon: “particle” of electromagnetic radiation. ZERO mass, carries a quantum (amount) of energy

• When an electrons falls back to it’s natural (non “excited state”) it’s seen a light and felt as heat

Photoelectric Effect (Solar Cells)

• Metals eject electrons called photoelectrons when light shines on them (energy not emitted continuously)

• Plank showed relationship between the intensity of light shined on metal (frequency) and amount of electrical current produce (Energy).

Plank’s Constant

E = h x v

E = radiant energy

h = 6.6262 x 10-34 Jxs (Plank’s Constant) = Energy of one photon

v = frequency of the radiation (Hz)

Frequency (v) and Energy (E) directly proportional!

De Broglie equation

• Wave-particle duality: Particles exhibit wave and particle properties (not just light but ALL matter)

λ = h / mv

m = mass of particleh = 6.6262 x 10-34 Jxs (Plank’s Constant)

Atomic Emission Spectrum