CHAPTER 5 The Structure of the Atom 5.4 Light and Spectroscopy
460 370 BC 1808 1870 1897 1910 1925 Today Democritus Atomism Dalton Modern atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle 2 5.4 Light and Spectroscopy
460 370 BC 1808 1870 1897 1910 1925 Today Democritus Atomism Dalton Modern atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle 3 5.4 Light and Spectroscopy
460 370 BC 1808 1870 1897 1910 1925 Today Democritus Atomism Dalton Modern atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle 4 5.4 Light and Spectroscopy
460 370 BC 1808 1870 1897 1910 1925 Today Democritus Atomism Dalton Modern atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle Do we have evidence to support these claims? 5 5.4 Light and Spectroscopy
A wave particle But light waves come in bundles of light (photons) and an electron behaves as a wave 6 5.4 Light and Spectroscopy
orbital: group of quantum states that have similar spatial shapes, labeled s, p, d, and f. 7 5.4 Light and Spectroscopy
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Lithium s 3 rd electron has to go into the 2 nd energy level One electron per quantum state Fill lowerenergy levels first 9 5.4 Light and Spectroscopy
Electromagnetic radiation. The photoelectric effect (where wave energy from the sun is absorbed by a metal and turned into electrical energy) and the fact that waves slow down when they go through a different medium (like water) indicates that the wave must have some type of particle property. 10 5.4 Light and Spectroscopy
frequency: the rate at which an oscillation repeats; one hertz (Hz) is a frequency of one oscillation per second. wavelength: the distance (separation) between any two successive peaks (or valleys) of a wave. 11 5.4 Light and Spectroscopy
The higher the frequency, the higher the energy 12 5.4 Light and Spectroscopy
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. 13 5.4 Light and Spectroscopy
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. 14 5.4 Light and Spectroscopy
Analyzing starlight with a prism (one of the first spectrometers) White light from a lamp or the sun is not truly white! 15 5.4 Light and Spectroscopy
Visible light is only a small range in the electromagnetic spectrum 16 5.4 Light and Spectroscopy
We are surrounded by electromagnetic energy 17 5.4 Light and Spectroscopy
18 increasing frequency increasing wavelength Light is a carrier of energy. Energy is proportional to frequency. Frequency is inversely proportional to wavelength.» Longer wavelength = lower frequency = lower energy.» Shorter wavelength = higher frequency = greater energy.
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On the scale of atoms Electrons Light Planck s constant (h) is used to calculate the energy and wavelength of electrons and photons 20 5.4 Light and Spectroscopy
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. 21 5.4 Light and Spectroscopy
Wavelength and frequency are related 22 5.4 Light and Spectroscopy
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? 23 5.4 Light and Spectroscopy
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: Given: Relationships: Frequency and energy 9 652 10 m c, E h 24 5.4 Light and Spectroscopy
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: Given: Relationships: Solve: Frequency and energy 9 652 10 m c, E h c 3 10 m / s 4.6 10 c therefore 9 652 10 m s 8 14 15 14 V s s E h 4.136 10 e 4.6 10 / 1.9 ev 25 5.4 Light and Spectroscopy
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: Given: Relationships: Solve: Frequency and energy 9 652 10 m c, E h c 3 10 m / s 4.6 10 c therefore 9 652 10 m s 8 14 15 14 V s s E h 4.136 10 e 4.6 10 / 1.9 ev 26 5.4 Light and Spectroscopy
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: Given: Relationships: Solve: Answer: Frequency and energy 9 652 10 m c, E h c 3 10 m / s 4.6 10 c therefore 9 652 10 m s 8 14 15 14 V s 1 / s E h 4.136 10 e 4.6 0 1.9 ev Since 1 Hz = 1/s, the frequency is 4.6 x 10 14 Hz and the energy is 1.9 ev. 27 5.4 Light and Spectroscopy
Light from an incandescent light bulb: prism all possible energy levels electron 28 5.4 Light and Spectroscopy
Light from pure hydrogen: prism fixed energy levels electron 29 5.4 Light and Spectroscopy
Line Emission Spectra of Excited Atoms Excited atoms emit light of only certain wavelengths The wavelengths of emitted light depend on the element. 30 5.4 Light and Spectroscopy
Hydrogen atoms can only absorb and emit light of very specific energies. 31 5.4 Light and Spectroscopy
Matter and light Why does the atom absorb only specific (discrete) energies? 32 5.4 Light and Spectroscopy
Matter and light Why does the atom absorb only specific (discrete) energies? Remember: only some energy levels are allowed. 33 5.4 Light and Spectroscopy
An excited lithium atom emitting a photon of red light to drop to a lower energy state. 34 5.4 Light and Spectroscopy
Electrons and Quanta Ground state the lowest energy position an e - can occupy. Excited state a temporary high-energy position. Quantum (pl. quanta) the amount of energy needed to move an e - to a higher energy level. 35 5.4 Light and Spectroscopy
Electrons and Quanta If an atom absorbs exactly 1 quantum of energy, an electron can be boosted from a ground state to an excited state. The electron is only in the excited state for a very short period of time. Soon the e - returns to its ground state and emits the quantum of energy as light. In some cases the emitted light is in the visible spectrum. 36 5.4 Light and Spectroscopy
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An excited H atom returns to a lower energy level. 38 5.4 Light and Spectroscopy
Matter and light Energy levels Energy levels Photon (energy) Energy of the photon matches a gap between levels Energy (light) is absorbed. Energy of the photon does not match a gap between levels Energy (light) passes through the atom. 39 5.4 Light and Spectroscopy
Matter and light Energy levels Photon (energy) another photon is emitted Energy of the photon matches a gap between levels Energy (light) is absorbed. specific color (wavelength) 40 5.4 Light and Spectroscopy
Each type of atom has a different electron structure. Each element has unique energy levels like a fingerprint. 41 5.4 Light and Spectroscopy
Flame Tests Flame test used to ID some metals in compounds. Each metal gives a flame a characteristic color. Can identify metals based on flame colors. 42 5.4 Light and Spectroscopy
Spectrum cards How to read the spectrum cards 43 5.4 Light and Spectroscopy
Spectrum cards Combinations of elements contain spectral lines from both. 44 5.4 Light and Spectroscopy
Visible light is only a small range of the electromagnetic spectrum. 45 5.4 Light and Spectroscopy
Each type of atom has a different electron structure. Each element has unique energy levels like a fingerprint. 46 5.4 Light and Spectroscopy