2 Properties of LightDifferent types of electromagnetic radiation (x-rays, radio waves, microwaves, etc…) SEEM to be very different from one another. Yet they share certain fundamental characteristics.3.0 x 108 m/sec is the speed of light!
3 A. WavelengthWavelength – distance between identical points on successive wavesUsually measured in nanometers
4 B. FrequencyFrequency – the number of complete wave cycles that pass a given point in one second: the unit is cycles/second but is written as sec-1, or Hertz.One wave in one second equals one Hertz!
5 AmplitudeAmplitude is the height of a wave. It is also measured in length units like nanometers, angstroms, etc.
6 A A A. Waves greater amplitude crest (intensity) origin trough greater frequency(color)
7 c = f EM Spectrum c: speed of light (3.00 108 m/s) Frequency & wavelength are inversely proportionalc = fc: speed of light (3.00 108 m/s): wavelength (m, nm, etc.)f: frequency (Hz)
8 EM Spectrum c = f Longer Wavelength means Lower Frequency Shorter Wavelength means Higher FrequencyHigher Frequency means Higher EnergyLower Frequency means Lower Energy
9 RangeThe range of visible light is from 400 to 700 nanometers. Low energy is colored red while high energy is colored violet.Violet: nmIndigo: nmBlue: nmGreen: nmYellow: nmOrange: nmRed: nm
10 Ephoton = hf E : engery of a photon (J) h: Plank’s constant (6.63 x J . sec)f: frequency (Hz or sec-1)
15 Examples3. What is the frequency of radiation whose wavelength is 2.20 x l0-6 nm? (1 m = 1,000,000,000 nm)Given:Work:c = 3.00 108 m/sλ = 2.20 x 10-6 nm(you have to change nm to m)f = ?f = c/ λf = 3.00 1082.20 x 10-15
17 Hydrogen Atom Line Emission Spectra When investigators passed electric current through a vacuum tube containing hydrogen gas at low pressure, they observed the emission of a characteristic pinkish glow. When a narrow beam of the emitted light was shined through a prism, it was separated into a series of specific frequencies (and therefore specific wavelengths, c =) of visible light. The bands of light were part of what is known as hydrogen’s LINE-EMISSION SPECTRUM. (page 95)
18 The lowest energy state of an atom is its ground state. A state in which an atom has a higher amount of energy is an excited state. When an excited atom returns to its ground state, it gives off energy.
19 B. Bohr Modele- exist only in orbits with specific amounts of energy called energy levelsTherefore…e- can only gain or lose certain amounts of energyonly certain photons are produced
20 B. Bohr Model6Energy of photon depends on the difference in energy levelsBohr’s calculated energies matched the IR, visible, and UV lines for the H atom54321
21 C. Other Elements Helium Each element has a unique bright-line emission spectrum.“Atomic Fingerprint”HeliumBohr’s calculations only worked for hydrogen!