Bohr Model and the Atomic Emission Spectra

Pre-Test and Unit Project

• Pre-Test- For Me Only
• Periodic Trends Project
• 75 Points
• Assessment Grade
• Final Draft Due Nov 7

Warm- Up

• Draw and label an atom of ⁴He

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• Turn it in to the front with your name, date, and class period

Demo

• On your own, think about and write some ideas for the following questions:
• What do you think is occurring on a subatomic level?
• Do you think any subatomic particles are moving? Why?
• Which subatomic particles do you think would move?
• How do you think they would move?

Bohr Model of the Atom

• Nucleus is composed of protons and neutrons
• Electrons are in orbitals outside of the nucleus
• Orbitals increase in energy as the go away from the nucleus

Increasing Energy

Orbitals Relate to Position on Periodic Table

• Period 1 corresponds to n=1
• Period 2 corresponds to n=2 and so on
• Orbitals get closer together further away from the nucleus

Emission Spectra

• When a beam of emitted light is shined through a prism, it is separated into the specific colors of the visible spectrum. This is called an emission-line spectrum.

Excited Electrons

• When an atom absorbs energy, electrons “jump” from ground state to an excited state

Release of Energy

• Excited electrons must “fall” back to ground state.
• When electrons fall, they release energy in the form of a photon of light

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• Absorb energy= Absorption
• Release energy= Emission

Energy (photon)

Atomic Emission

• Electrons give off different amounts of energy depending on the orbital that they fall from and the orbital that they fall to
• This energy corresponds to different wavelengths and frequencies of light

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Bohr Model of Hydrogen Atom

Absorption- energy added

Emission- energy released

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• Colors of line spectrum show how much energy the electrons release when they fall to ground state
• Notice the only certain amounts of energy can be absorbed or emitted- quanta.

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Atomic Emission Spectra

Energy (photon)

• In groups of two, discuss for 3 minutes how the flame test relates to the Bohr Shell Model and the Atomic Emission Spectra.
• What was occurring on the subatomic level?
• Why did the different elements burn different colors?
• Absorption and emission.
• Following your discussion, write a short paragraph describing the topics you discussed. It MUST include the following:
• How did absorption occur during the flame test?
• How did emission occur? How could you tell?
• Why did each element burn a different color?
• Which element do you think had electrons fall from the highest shell? (hint: how does energy relate to color?)

Writing Activity: Turn in!

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• When the element is placed in the flame, electrons absorb energy and move to the excited state
• The color of the light given off corresponds to the energy difference between the ground and excited states of the element.
• Because each element has a unique energy difference between the ground and excited states, each element emits a unique color when heated.

Flame test

Emission Tube Demo

• In this lab, gases receive electrical energy to excite the electrons.
• The electrons give off light in unique wavelengths and frequencies.
• The emitted light is passed through a spectroscope, which breaks light into its bright line emission spectrum.
• Each element produces a unique bright-line spectrum because each has a different number of electrons.
• The lines produced depends on the electron transition in that particular atom.

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Emission Tube Demo

• Get a white piece of paper, colored pencils, and a spectrometer
• 1. Fluorescent Bulb
• Point the slit of your spectrometer towards the light and look through the other end. Spin the eye piece until you see a thin vertical rainbow (continuous spectrum) and distinct horizontal lines of color with black in between (bright line spectrum)
• Label “Fluorescent Bulb” on your paper and draw the bright line spectrum below it

Fluorescent Emission Spectra

Bright Line Spectrum:

Continuous Spectrum:

Emission Tube Demo

2.Label the your paper “Hydrogen”

Look at the hydrogen emission tube with your spectrometer and draw the bright line spectrum on your paper

3. Repeat Step 2 for the other emission tubes I show you

Bright Line Spectrum of Demos

Emission Tube Questions

• What is the difference between a continuous spectrum and a bright line spectrum?
• How were the bright line spectrums for each tube different?
• Why were the bright line spectrums different?
• Draw a picture of absorption and emission.

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HomeWork Due Next Class

• Finish Flame Test Worksheet
• Finish Emission Tube Questions

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Question to think about:

• What would happen if we looked at the Flame Test through a spectroscope?