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CHAPTER 5. The Structure of the Atom. 5.4 Light and Spectroscopy. Today. 460 – 370 BC. 1808. 1897. 1910. 1925. 1870. Democritus Atomism. Crookes Cathode rays. Thomson Discovery of the electron. Rutherford Discovery of the nucleus. Pauli Pauli exclusion principle. Dalton

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## CHAPTER 5

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**CHAPTER 5**The Structure of the Atom 5.4 Light and Spectroscopy**Today**460 – 370 BC 1808 1897 1910 1925 1870 Democritus Atomism Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle Dalton “Modern” atomic theory**Today**460 – 370 BC 1808 1897 1910 1925 1870 Crookes Cathode rays Rutherford Discovery of the nucleus Democritus Atomism Thomson Discovery of the electron Pauli Pauli exclusion principle Dalton “Modern” atomic theory**Today**460 – 370 BC 1808 1897 1910 1925 1870 Democritus Atomism Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle Dalton “Modern” atomic theory**Today**460 – 370 BC 1808 1897 1910 1925 1870 Democritus Atomism Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle Dalton “Modern” atomic theory Do we have evidence to support these claims?**Light is a form of electromagnetic energy that comes from**electrons in atoms The human eye can only detect a certain range of that energy: the visible spectrum.**Light is a form ofelectromagneticenergy that comes from**electrons in atoms Thehuman eyecan only detect a certain range of that energy: thevisible spectrum.**Analyzing starlight with a prism**(one of the first spectrometers) White light from a lamp or the sun is not truly white!**Visible light is only a small range in the electromagnetic**spectrum**Energy of a photon**Remember that light travels as bundles called photons A very small unit of energy 1 electron volt (eV) = 1.602 x 10–19 J.**The wavelength of red laser light is 652 nm.**What is its frequency? How much energy does a photon of this light have in electron volts?**The wavelength of red laser light is 652 nm.**What is its frequency? How much energy does a photon of this light have in electron volts? Asked:Frequency and energy Given: Relationships:**The wavelength of red laser light is 652 nm.**What is its frequency? How much energy does a photon of this light have in electron volts? Asked: Frequency and energy Given: Relationships: Solve:**The wavelength of red laser light is 652 nm.**What is its frequency? How much energy does a photon of this light have in electron volts? Asked: Frequency and energy Given: Relationships: Solve:**The wavelength of red laser light is 652 nm.**What is its frequency? How much energy does a photon of this light have in electron volts? Asked: Frequency and energy Given: Relationships: Solve: Answer:Since 1 Hz = 1/s, the frequency is 4.6 x 1014 Hz and the energy is 1.9 eV.**Light from an incandescent light bulb:**prism all possible energy levels electron**Light from pure hydrogen:**prism fixed energy levels electron**Hydrogen atoms can only absorb and emit light of very**specific energies.**Matter and light**Why does the atom absorb only specific (discrete) energies?**Matter and light**Why does the atom absorb only specific (discrete) energies? Remember: only some energy levels are allowed.**Matter and light**Energy levels Energy levels Photon (energy) Energy of the photon matches a gap between levels Energy of the photon does not match a gap between levels Energy (light) passes through the atom. Energy (light) is absorbed.**Matter and light**Energy levels Photon (energy) another photon is emitted Energy of the photon matches a gap between levels specific color (wavelength) Energy (light) is absorbed.**Each type of atom has a different electron structure.**Each element has unique energy levels like afingerprint.**How to read the spectrum cards**Spectrum cards**Spectrum cards**Combinations of elements contain spectral lines from both.**Reemission of light has two steps:**Energy levels Photon (energy) Photon absorbed Photon emitted Energy of the photon matches a gap between levels**Range of energies**Emission spectrum Energy levels Photon (energy) Absorption spectrum**Visible light is only a small range of the electromagnetic**spectrum.**Each type of atom has a different electron structure.**Each element has unique energy levels like afingerprint.

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