Waves and particles Ch. 4

Waves Wavelength (λ)-the distance between corresponding points on adjacent waves. meters, centimeters, or nanometers Frequency (ν) -defined as the number of waves that pass a given point in a specific time. hertz (Hz) = 1/s Amplitude (A) - distance from the origin to the trough or crest

EM Spectrum High Energy Low Energy

EM Spectrum High Low Energy Energy R O Y G. B I V red orange yellow green blue indigo violet

Frequency and Wavelength c=λv c= speed of light m/s, λ= wavelength m, v= frequency s-1 or 1/s c is a constant that equals 3.00x108 m/s Therefore frequency and wavelength are inversely proportional.

This is the answer you should get: Ex. Find the frequency of a photon with a wavelength of 434 nm ν = c/λ λ = 434 nm c = 3.00 × 108 m/s Solve for v This is the answer you should get: ν = 6.91 × 1014 Hz

Quantum Theory Planck (1900) Observed - emission of light from hot objects Concluded - energy is emitted in small, specific amounts (quanta) Quantum - minimum amount of energy change

Quantum Theory Einstein (1905) Observed - photoelectric effect Concluded - light has properties of both waves and particles “wave-particle duality” Photon - particle of light that carries a quantum of energy

Photoelectric Effect photoelectric effect- emission of electrons from a metal when light shines on the metal. no electrons were emitted if the light’s frequency was below a certain minimum regardless of lights intensity. light form of energy able to knock loose an electron from a metal. wave theory of light- light any frequency could supply enough energy to eject an electron.

Quantum Theory The energy of a photon is proportional to its frequency. E=h ν E: energy (J, joules) h: Planck’s constant(6.6262 ×10-34 J·s) ν: frequency (Hz)

EX: Find the energy of a red photon with a frequency of 4.57 × 1014 Hz. GIVEN: ____________________ E = ? ν = 4.57 × 1014 Hz h = 6.6262 × 10-34 J·s WORK: ______________________ E = hν E = (6.6262 × 10-34 J·s) (4.57 × 1014 Hz) E = 3.03 × 10-19 J

Bohr Model of an Atom

Bohr Model e- exist only in orbits with specific amounts of energy called energy levels Therefore… e- can only gain or lose certain amounts of energy only certain photons are produced

Bohr Model Energy of photon depends on the difference in energy levels Bohr’s calculated energies matched the IR, visible, and UV lines for the H atom 6 5 4 3 2 1

Bohr’s calculations only worked for hydrogen! ☹ Other Elements Each element has a unique bright-line emission spectrum. “Atomic Fingerprint” Helium Bohr’s calculations only worked for hydrogen! ☹