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Atomic Theory and Spectroscopy Electromagnetic Radiation Energy emitted by electrons can be detected at any part of the electromagnetic spectrum Energy.

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Presentation on theme: "Atomic Theory and Spectroscopy Electromagnetic Radiation Energy emitted by electrons can be detected at any part of the electromagnetic spectrum Energy."— Presentation transcript:

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2 Atomic Theory and Spectroscopy

3 Electromagnetic Radiation Energy emitted by electrons can be detected at any part of the electromagnetic spectrum Energy emitted by electrons can be detected at any part of the electromagnetic spectrum

4 Electromagnetic Radiation So, just what is EMR? - an oscillating electric and magnetic field which travels through space OR - a discrete series of “particles” that possess a specific energy but have no mass BOTH!

5 Waves

6 Measuring Waves Two properties can be measured: Two properties can be measured: Wavelength ( ) Wavelength ( ) The distance from the same point on successive waves (measured in meters) The distance from the same point on successive waves (measured in meters)

7 Measuring Waves Frequency ( ) Frequency ( ) The number of times a wave travels up and down per second The number of times a wave travels up and down per second Measured in cycles per second or hertz (Hz) Measured in cycles per second or hertz (Hz)

8 The frequency ( ) is the number of wave crests per second which pass a reference point.

9 The amplitude (A) is the height of the wave

10 Measuring radiation

11 Measuring Radiation All radiation constantly travels through space at the same velocity (speed) = All radiation constantly travels through space at the same velocity (speed) = 3.0 x 10 8 m/s (299,792,458 meters per second) The speed of electromagnetic radiation --- “The speed of light” = c

12 c= c= c = 3.0 x10 8 If either the frequency or wavelength is known, the other can be calculated

13 A red light has a wavelength of 728 *10 -9 m. A red light has a wavelength of 728 *10 -9 m. What is the speed of the wave in m/s? What is the speed of the wave in m/s? What is the frequency of the light?

14 A certain blue light has a frequency of 6.91 x Hz. What is the wavelength of the light?

15 Determine the wave length of light with a speed of 50*10 6 Hz (/sec)

16 If I have a wavelength of 780 *10 -9 m and what is the frequency?

17 Microwave ovens often employ radiation with a frequency of 2.45 x 10 9 /s. What is the wavelength (in cm) of this radiation?

18 A purple light has a frequency of 7.42 x Hz. What is its wavelength? What is the energy of one quanta of light A purple light has a frequency of 7.42 x Hz. What is its wavelength? What is the energy of one quanta of light

19 m/s Not just a good idea, it’s the law!

20 Properties of Light Form of energy, detectable with the eye, which can be transmitted from one place to another at a finite velocity

21 Theory of Light Two complimentary theories to explain how light behaves and the form by which it travels: Particle Theory Wave Theory

22 Particle Theory Release of a photon

23 Electromagnetic spectrum and Energy longest

24 Planck’s Quantum Theory In 1900, German Physicist Max Planck proposed: “Radiant energy may only be absorbed or emitted in discrete amounts: quanta.”

25 Electromagnetic spectrum and Energy Planck discovered the energy of a wave or photon of light is constant Planck discovered the energy of a wave or photon of light is constant h = (6.63 x J/Hz) Planck’s constant (h)

26 Energy and Radiation If the frequency of a wave is known, then the energy of the wave can be calculated as well in the same manner If the frequency of a wave is known, then the energy of the wave can be calculated as well in the same manner E=h E=h Or E= h (c/ )

27 Energy and Radiation E=hv Sample: What is the energy of a wave which has a frequency of Hz? Sample: What is the energy of a wave which has a frequency of x 10 8 Hz? h = 6.63 x J Hz = x 10 8 Hz 6.86 x J E = 6.63 x J Hz x 10 8 Hz =

28 Photons Photons are a particle of radiation or an individual quantum of light Photons are a particle of radiation or an individual quantum of light Quantum is a finite quantity of energy that can be gained or lost by an atom Quantum is a finite quantity of energy that can be gained or lost by an atom

29 The Nature of Light and Radiation If e - are exposed to energy which matches those levels (a photon), they leap to unstable higher energy levels. As they fall back they emit that energy ( a photon) at a wavelength and frequency which can be detected. /

30 Photoelectric Effect Albert Einstein proposed that light not only behaves as a wave, but as a particle too Albert Einstein proposed that light not only behaves as a wave, but as a particle too Albert Einstein did not get the Nobel Prize for Relativity. He received it for work that he did between 1905 and 1911 on the Photoelectric Effect. Albert Einstein did not get the Nobel Prize for Relativity. He received it for work that he did between 1905 and 1911 on the Photoelectric Effect.

31 Photoelectric Effect In 1905, Einstein applied this quantum theory to explain the photoelectric effect:

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33 Photoelectric Effect -if EMR was absorbed as a wave, then the number of electrons ejected and the energy of the electrons ejected should vary only with the intensity of the light

34 e-e- e-e- e-e- Einstein Photoelectric Effect E hv - E e - = Ionization Energy hvhv e-e-

35 PhotoelectricPhotoelectric Effect Effect PhotoelectricEffect NUMBER of e-: does vary with EMR intensity ENERGY of e-: vary only with MR frequency AND: no effect if freq is below a threshold value!

36 Photoelectric effect The reason that certain types of light cause this effect but others do not has to do with threshold energy The reason that certain types of light cause this effect but others do not has to do with threshold energy Remember that electrons must gain energy in certain amounts (  E = h ) Remember that electrons must gain energy in certain amounts (  E = h ) Only certain types of light with “just the right” frequency can cause electrons to become excited Only certain types of light with “just the right” frequency can cause electrons to become excited

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38 The Nature of Light and Radiation /

39 Photoelectric Effect View EMR as a collection of particles(called photons), with each photon having the following energy: E = hν

40 Photoelectric Effect Each photon will cause an electron to be ejected IF the energy of the photon is above a minimum (threshold) value. Any energy of the photon above that needed to eject the electron would be transferred to the electron as kinetic energy

41 Photoelectric Effect Increased EMR intensity translates to an increase in the number of photons (increasing the number of electrons ejected)

42 Einstein Einstein did not receive his Nobel Prize of the theory of relativity but for his work on the photoelectric effect Einstein did not receive his Nobel Prize of the theory of relativity but for his work on the photoelectric effect

43 Typed of Spectra

44 Hydrogen Line Spectrum Because hydrogen atoms emit only specific frequencies of light indicate that the energy differenced between the atom states are fixed Because hydrogen atoms emit only specific frequencies of light indicate that the energy differenced between the atom states are fixed

45 The Bohr Atom The electron in a hydrogen atom can exist only in discrete orbits The orbits are circular paths about the nucleus at varying radii

46 Light leads to Electrons Electrons exist in specific, discrete levels or quanta of energy Electrons exist in specific, discrete levels or quanta of energy The lowest energy of each electron is known as its ground state The lowest energy of each electron is known as its ground state If the right amount (quantum) of energy is applied, then an electron will “leap” to another energy level If the right amount (quantum) of energy is applied, then an electron will “leap” to another energy level

47 The Bohr Atom Each orbit corresponds to a particular energy Orbit energies increase with increasing radii

48 The Bohr Atom The lowest energy orbit is called the ground state After absorbing energy, the e- jumps to a higher energy orbit (an excited state)

49 The Bohr Atom When the e- drops down to a lower energy orbit, the energy lost can be given off as a quantum of light The energy of the photon emitted is equal to the difference in energies of the two orbits involved

50 Bohr’s Model of H Atom Linked an atom’s e- to photon emission Linked an atom’s e- to photon emission Said that e’ can circle the nucleus only is specific paths or orbits. Said that e’ can circle the nucleus only is specific paths or orbits. Orbits are separated from the nucleus by large empty spaces (nodes) where the e- cannot exist. (Rungs on a ladder) Orbits are separated from the nucleus by large empty spaces (nodes) where the e- cannot exist. (Rungs on a ladder) Remember, E increases as e- are further from the nucleus. Remember, E increases as e- are further from the nucleus.

51 Bohr’s Model of H Atom While an e- is in orbit, it cannot gain nor lose E While an e- is in orbit, it cannot gain nor lose E It can, move to a higher E level IF it gains the amount of E = to the difference between the higher E orbit and the lower energy orbit. It can, move to a higher E level IF it gains the amount of E = to the difference between the higher E orbit and the lower energy orbit. When falls, it emits a PHOTON = to the difference. When falls, it emits a PHOTON = to the difference. Absorption gains E/Emission gives off E Absorption gains E/Emission gives off E

52 Take the good with the bad (Bohr’s Model) Good: Good: Led scientists to believe a similar model could be applied to all atoms. Led scientists to believe a similar model could be applied to all atoms. Bad: Bad: Yikes!!! Did not explain the spectra of atoms with more than one e’ or chemical behavior of atoms! Yikes!!! Did not explain the spectra of atoms with more than one e’ or chemical behavior of atoms!

53 The Bohr Model of the Atom Neils Bohr I pictured electrons orbiting the nucleus much like planets orbiting the sun. But I was wrong! They’re more like bees around a hive. WRONG!!!

54 The Nature of Electrons If light acts as both particles and waves, then so do electrons. If light acts as both particles and waves, then so do electrons. If electrons act like waves, then how can we locate them? If electrons act like waves, then how can we locate them?

55 Atoms are like onions and ogres they have lots of layers plantanswers.tamu.edu

56 Orbits We like to draw orbits as circular We like to draw orbits as circular but they really aren’t

57 Orbits Turns out, there's no reason to assume that electron orbits are circular. Turns out, there's no reason to assume that electron orbits are circular.

58 Orbits There are lots of paths an electron can take in order to get around the nucleus. There are lots of paths an electron can take in order to get around the nucleus. (or through the nucleus) (or through the nucleus)

59 Orbits In fact it's very rare for an atom's electron to be in a circular orbit. In fact it's very rare for an atom's electron to be in a circular orbit.

60 Electron Facts The electron moves at different speeds. Fast near the nucleus and slow when it's far from the nucleus. The electron moves at different speeds. Fast near the nucleus and slow when it's far from the nucleus.

61 Well we really don’t Because atoms are so small, no one can see them. Because atoms are so small, no one can see them. For this reason, we just can't say exactly where the electron is, as it moves about the nucleus. In those orbit pictures, we know the electron will be somewhere on the white orbit lines. For this reason, we just can't say exactly where the electron is, as it moves about the nucleus. In those orbit pictures, we know the electron will be somewhere on the white orbit lines.

62 This makes the models involving orbits, whether circles, or ellipses, wrong, because the orbits are pretty specific about the electron's location. This makes the models involving orbits, whether circles, or ellipses, wrong, because the orbits are pretty specific about the electron's location.

63 So how do we locate electrons in the modern atom? Quantum Numbers

64 Specify the properties of atomic orbitals and the properties of electrons in orbital

65 Quantum Numbers Don’t tell us where the electron is, just where it's most likely to be. Don’t tell us where the electron is, just where it's most likely to be. The probable location of electrons are described using an address The probable location of electrons are described using an address

66 The four quantum numbers their symbols are n, l, m and s. EVERY electron in an atom has a specific, unique set of these four quantum numbers.

67 Quantum Numbers There are 4 parts to each address Principle quantum number (n) Principle quantum number (n) Angular quantum number (l) Angular quantum number (l) Magnetic quantum number (m) Magnetic quantum number (m) Spin quantum number (s) Spin quantum number (s)

68 The Principal Quantum Number n The main energy level of an electron

69 Principal Quantum Number (n) Describes the size of the orbital. Describes the size of the orbital. Since the distance from of an electron from the nucleus is directly proportional to the energy of the electron Since the distance from of an electron from the nucleus is directly proportional to the energy of the electron It must be a whole number n=1, n=2 … It must be a whole number n=1, n=2 …

70 Angular quantum number ( l ) Azimunthal Describes the shape Describes the shape The secondary quantum number divides the shells into smaller groups of orbitals called subshells (sublevels). The secondary quantum number divides the shells into smaller groups of orbitals called subshells (sublevels). s p d f g h... s p d f g h...

71 Angular (Azimuthal) Momentum Quantum Number LetterShape sSphere pDumbell dCloverleaf f“funky”

72 Each suborbital can hold a maximum of 2 electrons per orbital Each suborbital can hold a maximum of 2 electrons per orbital

73 Angular (Azimuthal) Momentum Quantum Number Letter Max number of suborbitals Max. # of e - s12 p36 d510 f714

74 Quantum Numbers The more crowded the dots are in a particular region, the better chance you have to finding your electron there.

75 s Orbital sphere

76 Orbitals of the same shape (s, for instance) grow larger as n increases… Nodes are regions of low probability within an orbital. Sizes of s orbitals

77 p Orbital dumbbell

78 two p Orbitals two p Orbitals

79 All three p Orbitals

80 d Orbitals Cloverleaf orbitalorbital

81 f Orbitals “funky” orbitalorbital

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83 Orbital filling table

84 The Magnetic Quantum Number m describes the orientation in space of a particular orbital. x, y, z

85 Magnetic quantum number (m) The orientation in space The orientation in space What axis the orbit is located on What axis the orbit is located on

86 The Spin Quantum Number s allows two electrons of opposite spin (or symmetry) into each orbital. +1/2 or -1/2  or 

87 Spin quantum number (s) +1/2-1/2

88 Aufbau (filling up) Principle the number of electrons in an atom is equal to the atomic number the number of electrons in an atom is equal to the atomic number each added electron will enter the orbitals in the order of increasing energy each added electron will enter the orbitals in the order of increasing energy an orbital can only hold 2 electrons. an orbital can only hold 2 electrons.

89 Hund’s Rule For orbitals of equal energy, one electron goes into each orbital until all orbitals are half-full. For orbitals of equal energy, one electron goes into each orbital until all orbitals are half-full. 1s 2 2s 2 2p 4

90 Aufbau Principle Lower-energy orbitals of an atom are filled with electrons first. Lower-energy orbitals of an atom are filled with electrons first. 1s 2s 2p 3s 3p 4s 3d 4p … 1s 2s 2p 3s 3p 4s 3d 4p …

91 Pauli Exclusion Principle No two electrons in an atom can have an identical set of four quantum numbers. (electrons sharing an orbital have different spins) No two electrons in an atom can have an identical set of four quantum numbers. (electrons sharing an orbital have different spins) 1s 2 2s 2

92 Key Terms Ground State Electron Configurations (1s 2 2s 2 …/Orbital Notations __ __ __ __ Ground State Electron Configurations (1s 2 2s 2 …/Orbital Notations __ __ __ __ Aufbau Principle (lowest first/periodic guide) Aufbau Principle (lowest first/periodic guide) Hund’s Rule: Single e’ before pairing begins Hund’s Rule: Single e’ before pairing begins Pauli Exclusion (up/down—no 2 e’ same set of quant. #’s) Pauli Exclusion (up/down—no 2 e’ same set of quant. #’s) Highest Occupied Level Highest Occupied Level Inner-Shell e’ Inner-Shell e’ Noble Gas Notation Noble Gas Notation

93 Spin Diagram for Hydrogen Electron configuration for Hydrogen 1s 1

94 Spin Diagram for Helium Electron configuration for Helium 1s 2

95 Spin Diagram for lithium Electron configuration for lithium 1s 2 2s 1

96 Spin Diagram for beryllium Electron configuration for berylium 1s 2 2s 2

97 Spin Diagram for boron Electron configuration for boron 1s 2 2s 2 2p 1

98 Spin Diagram for carbon Electron configuration for carbon 1s 2 2s 2 2p 2

99 Spin Diagram for nitrogen Electron configuration for nitrogen 1s 2 2s 2 2p 3

100 Spin Diagram for oxygen Electron configuration for oxygen 1s 2 2s 2 2p 4

101 Spin Diagram for fluorine Electron configuration for fluorine 1s 2 2s 2 2p 5

102 Spin Diagram for neon Electron configuration for neon 1s 2 2s 2 2p 6

103 Standard Notation or Complete electron configuration of Fluorine Main Energy Level Numbers 1, 2, 2 Sublevels Number of electrons in the sub level 2,2,5 1s 2 2s 2 2p 5

104 Shorthand Notation or Noble Gas Configuraiton Use the last noble gas that is located in the periodic table right before the element. Use the last noble gas that is located in the periodic table right before the element. Write the symbol of the noble gas in brackets. Write the symbol of the noble gas in brackets. Write the remaining configuration after the brackets. Write the remaining configuration after the brackets. Ex: Fluorine: [He] 2s 2 2p 5 Ex: Fluorine: [He] 2s 2 2p 5

105 Blocks in the Periodic Table

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108 You broke your big toe! The x ray they take of toe uses waves that have a length 2.19 x m. What is the speed of the wave in m/s? What is the wavelength in nm? What is the frequency of the x ray? You broke your big toe! The x ray they take of toe uses waves that have a length 2.19 x m. What is the speed of the wave in m/s? What is the wavelength in nm? What is the frequency of the x ray?


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