# Entry Task: October 12 th Friday Question: What makes up the colors in a rainbow? What other types of waves exist? You have 5 minutes!

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Entry Task: October 12 th Friday Question: What makes up the colors in a rainbow? What other types of waves exist? You have 5 minutes!

Agenda: Sign off and discuss Ch. 5 sec 1 reading and its worksheet –I’m SPRINTING through this!!!

Ch. 5 Electrons in Atoms

I CAN…… Explain the relationship of light with electron behavior. Compare Bohr’s and quantum mechanical model of the atom Express the arrangement of electrons in atoms through orbital notations, electron configurations, and electron dot structures

The timeline shows the development of atomic models from 1803 to 1911

5.1 Light and Quantized Energy Why was Rutherford’s model of the atom incomplete? Rutherford's model didn’t explain: The arrangement of electrons The electrons attraction to nucleus Differences in chemical behaviors in different elements

5.1 Light and Quantized Energy What relationship did early scientist observe about elements, chemical behavior and light? Certain elements emit visible light when heated by a flame. Analysis of the emitted light revealed that an elements chemical behavior is related to the arrangement of the electrons in its atom.

Wave characteristics All waves have these characteristics Wavelength (λ)- measures crest to crest- it’s a length Frequency (ν)- is the number of waves past a given point per second. Hertz is 1 wave per second Amplitude- is the height of the wave from the crest to the midpoint (origin) Speed- ALWAYS at the speed of light. Speed is the product of wavelength and frequency 3.00 x 10 8 m/s C= λ ν

Wavelength and frequency are inversely related

5.1 Light and Quantized Energy What can’t the wave model of light explain? It can’t explain why heated objects emit only certain frequencies of light at a given temperature, or why some metals emit electrons when colored light of a certain frequency shines on them

5.1 Light and Quantized Energy What happens when an object like a piece of iron is heated? As the iron gets hotter it changes color. The hotter it gets the more kinetic energy the material possesses.

5.1 Light and Quantized Energy What do the different colors (emitted from heated objects) of light correspond to? The changing of energy correspond to electrons being emitted at different frequencies Different frequencies, different wavelengths therefore different colors. Heated object  kinetic energy  color (different λ & ν)

Quantum concept Define quanta: Matter can gain or lose energy only in small specific amounts of quanta. Define quantum Its the minimum amount of energy that can be gained or lost by an atom.

5.1 Light and Quantized Energy How come when we heat a cup of water in the microwave we don’t observe a step-by step heating of the water? The water’s temperature increase in infinitesimal steps, as its molecule absorb quanta of energy. Because the steps are so small, the temperature seems to rise in a continuous, rather than a stepwise, manner

Quantum concept E (quantum) = hv The packet of energy (quantum) is equal to the amount of heat (Planck’s constant) times frequency Amount of quantum energy = heat energy times frequency Violet light has greater energy than red.

Photoelectric Effect Electrons are released from the surface of metal when a specific frequency of light shines on it. This phenomena marries that light behaves wavelike and particlelike. Photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy.

Photoelectric Effect What did Einstein proposed about the duel wave- particle model of light? He proposed that electromagnetic radiation has both wavelike and particlelike nature. While a beam of light has many wavelike characteristics, it can also be though of as a stream of tiny particles, or bundles of energy, called photons

Photoelectric Effect E photon = hv Einstein came up with a this equation, the energy needed to “kick” an electron off the surface of metal needs a specific amount of energy and frequency of light

Atomic Emission Spectra What is an atomic emission spectrum? –When a gaseous element is excited with electricity and its light is passed through a prism a atomic emission spectrum is produced. –Emission spectrum is a set of frequencies (color) emitted by the excited atoms of an element –It’s the elements “fingerprint”

Atomic Emission Spectra When high voltage passes through a sample of an element –Electrons absorb a specific amount of energy –Electrons jump out of their orbit to a distinct distance from the nucleus –Electrons lose energy and drop back down to its ground state –Releasing a distinct amount of energy as a form of light

Close up view of Bohr’s atomic model/energy levels http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swf http://phet.colorado.edu/en/simulation/hydrogen-atom

Summary Scientist were trying to figure out electrons Why didn’t the electrons (-) collapse into the nucleus (+)? Where were they located around the nucleus? What was the connection between electrons and light?

Summary Light First!- As a Wave Light behaves like waves having wave characteristics Light is a form of Electromagnetic radiation. Travels at the speed of light 3.00 x 10 8 m/s (c). C= wavelength times frequency

Summary Light First!- As a particle Heated objects glow and emit light. Different wavelength of light at different temperatures Energy is absorbed or released are discrete packets called quanta. E quantum = hv This equation allows you to figure out how much energy (quanta) is associate with a particular frequency h is 6.026 x 10 -34 J and v is frequency of the wave

Summary Light First!- As a particle Light of a particular frequency, when shined on metal will eject excited electrons. This means that electrons have a “window” as to a specific amount that will get them excited- why? Einstein came up with light and other electromagnetic radiation behaves as a wave and particles. E photons = hv h is 6.026 x 10 -34 J and v is frequency of the wave Photons- particles with no mass but carries a quantum of energy

Homework: Ch. 5 sec. 2 reading

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