Warm Up What is the wavelength defined as? You are given the wavelength of a particle as being 6.3 x 10 -5 m. What is the frequency of the particle? You are given the frequency of a particle as 7.43 x 1014 Hz. What is the wavelength? HINT: Speed of light = 3.00 x 108 m/s

Unit Three, Day Two Kimrey 18 September 2012 Chemistry Unit Three, Day Two Kimrey 18 September 2012

Electromagnetic Spectrum Shows the different types of radiation – different wavelengths.

Radio Waves Radio waves are electromagnetic waves with the longest wavelengths (longer than 1mm) They are used in communications, radar, microwaves, and MRIs

Microwaves Microwaves are radio waves with wavelengths less than 30 cm but longer than 1mm Cell phones and satellites use microwaves Microwaves in microwave ovens cause water molecules to rotate, heating your food

Infrared Waves Infrared waves have wavelengths between 1mm and 750 billionths of a meter Thermal energy travels in infrared waves Remote controls and CD-ROM drives also use infrared waves

Visible Light The visible spectrum is the light we can see In order from largest wavelength to smallest: Red, Orange, Yellow, Green, Blue, Indigo, Violet (Roy G Biv) The color you see is the color that is reflected. White is all colors, black is no color. The longer the wavelength, the less penetrating (including less dangerous to cells)

Visible Light (ROYGBIV)

Ultraviolet Waves Ultraviolet, or UV waves, have wavelengths of 400 billionths to 10 billionths of a meter UV waves can cause skin damage such as sunburn, wrinkling, and cancer

Ultraviolet Light UV light enables your body to make vitamin D UV waves can kill bacteria by damaging its DNA

X-Rays X-rays have wavelengths between ten billionths of a meter and ten trillionths of a meter X rays are commonly used by doctors and dentists

Gamma Rays Gamma waves have wavelengths shorter than 10 trillionths of a meter Gamma rays are produced by radioactive decay or other subatomic processes

The Bohr Model Created by Niels Bohr in 1913. Related the energy of an electron to the orbital it would occupy. Similar to the model of the solar system with the nucleus as the sun.

1st shell can hold 2 electrons. 2nd can hold 8. 3rd can hold 18 4th can hold 32

Making Bohr Models Step One: Write the number of protons and neutrons in the nucleus. Step Two: Add electrons in their appropriate orbitals until you have reached the correct number of electrons.

Example Draw a Bohr model for Mg-24.

You Try Draw a Bohr model for the following: Nitrogen-14 Aluminum -27 Sodium-23+1

Conclusions from the Bohr Model Electrons are both Particles AND waves. We cannot know for certain where an electron is. We cannot know for certain how fast an electron is moving. The more we know about the location of an electron the less we know about its’ movement and vice versa.

Bohr Model and Light Bohr went a step further as well, he determined that each orbital corresponded to a certain energy level. As electrons become excited they can “jump” to a higher energy level. When these electrons return to their ground state (normal energy level) they emit the difference in energy levels. NOTE!!! Electrons can ONLY exist at a specific orbital NOT between orbitals.

Reading the Bohr Model

Example What is the wavelength of light emitted when an electron goes energy level 4 to energy level 1? (n=4  n=1) 97 nm

You Try What is the wavelength of light emitted when an electron goes from n= 3 to n = 2? What type of light would this be classified as? A photon with a wavelength of 656 nm is emitted from a hydrogen atom. What energy state did this electron start in and end in?

Bohr Model for H Atom

Example Problems What type of light has a wavelength of 1 x 10-11 m? What type of light is released when an electron jumps from = 4 to n = 1 in a Hydrogen atom? What type of light has a wavelength of 6.3 x 10 -7m? Is light energy released or absorbed in the following jumps of an electron in a Hydrogen atom? n=1 to n = 3 n = 2 to n = 5 n = 6 to n = 3 n = 2 to n = 3 Rank the following types of light in increasing energy: X – ray, green light, microwaves, violet light.