Atomic Spectroscopy and the Bohr Model A

Atomic Spectroscopy and the Bohr Model A. Light as a Wave

Light is a type of electromagnetic radiation that travels through space as a wave.

gamma rays x-rays UV radio waves micro waves red light green light Parts of an EM Wave

distance between wave crests measured in (m or nm) Parts of an EM Wave

2. Frequency- symbol is - how fast a wave oscillates - number of wavelengths per second - units are called hertz (Hz) 3. Wave Speed- measured in m/s - symbol is c - regardless of wavelength or frequency all EM radiation travels at a constant speed.

- 300,000,000 m/s 3.0 x 108 m/s 4. There is a mathematical relationship between wavelength and the frequency of a wave.

- The shorter the wavelength the higher the frequency - The longer the wavelength the lower the frequency

Calculated using the equation: = frequency (Hz) speed of light wavelength (m) (m/s) Parts of an EM wave 5. Light energy comes in packets called photons

*We say that light is quantized

Ephoton= h

h = Planck's constant = 6.626 x 10-34 J*s

If you substitute = frequency (Hz) speed of light wavelength (m) (m/s)

Ephoton= h*c Summary Part A: • Light = electromagnetic waves • Three characteristics > wavelength > frequency > speed > speed = wavelength x frequency

• Light is quantized (packets of energy) B. Light through a prism

When light is passed through a prism, the color components of light can be separated. 1.Continuous Spectrum

Shows all of the wavelengths of light that are being emitted by white light. The light is separated into a continuous ROYGBIV array or spectrum of colors.

White light is a mixture of all of the different colors of light.

The prism separates them up. 2. Emission spectrum

Shows the specific frequencies of light emitted by a specific atom that is being excited (energy is added)

*Atoms can be identified by the light they emit. They have a unique emission spectrum. Summary Part B: • Prisms separate light into components. • Continuous spectrum - think rainbow (ROYGBIV) • Emission spectrum - identifies atoms. C. Bohr Model

Scientist’s had a hard time explaining line spectra. - Why were there specific lines of color instead of all the colors? - Why were the colors always the same for a specific element? Niels Bohr Developed model for the atom that explained the atomic spectra. Planetary orbital model Niels Bohr 1. Electrons go around an atom's nucleus in circular orbits. 2. Circular orbits are different distances from the nucleus. 3. Energy of an electron depends on its distance from the nucleus. Niels Bohr 4. When an atom absorbs a photon of light, it is absorbing energy. > Absorption of a photon: low potential energy electron becomes high potential energy electron. > Emission of a photon: A high potential energy electron loses some of its energy, electron moves closer to nucleus Niels Bohr 5. Since light energy is quantized, the energy of an electron must also be quantized. *An electron can only have discrete amounts of potential energy.

With in the atom, there are energy levels.

Electrons cannot be "inbetween" energy levels

**Bohr's model ONLY WORKS FOR HYDROGEN.

Still, it is a good conceptual model to explain many phenomena...

Including emission spectra and fireworks!