Atomic Theory and Spectroscopy Electromagnetic Radiation Energy emitted by electrons can be detected...
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Transcript of Atomic Theory and Spectroscopy Electromagnetic Radiation Energy emitted by electrons can be detected...
Atomic Theory and Atomic Theory and SpectroscopySpectroscopy
Electromagnetic RadiationElectromagnetic Radiation
Energy emitted by electrons can be Energy emitted by electrons can be detected at any part of the detected at any part of the electromagnetic spectrumelectromagnetic spectrum
Electromagnetic RadiationElectromagnetic Radiation
So, just what is EMR? - an oscillating electric and magnetic fieldwhich travels through spaceOR- a discrete series of “particles” that possess aspecific energy but have no mass
BOTH!
WavesWaves
Measuring WavesMeasuring Waves
Two properties can be measured:Two properties can be measured: Wavelength (Wavelength () )
The distance from the same point on The distance from the same point on successive waves (measured in meters)successive waves (measured in meters)
Measuring WavesMeasuring Waves
Frequency (Frequency ()) The number of times a wave travels up and The number of times a wave travels up and
down per second down per second Measured in cycles per second or hertz (Hz)Measured in cycles per second or hertz (Hz)
The frequency (The frequency ()) is the number of wave is the number of wave crests per second which pass a crests per second which pass a
reference point. reference point.
The amplitude (A) is the The amplitude (A) is the height of the waveheight of the wave
Measuring radiationMeasuring radiation
Measuring RadiationMeasuring Radiation
All radiation All radiation constantlyconstantly travels through travels through space at the same velocity (speed) =space at the same velocity (speed) =
3.0 x 103.0 x 1088 m/s m/s
(299,792,458 meters per second)(299,792,458 meters per second)
The speed of electromagnetic radiation The speed of electromagnetic radiation ---“The speed of light” = c---“The speed of light” = c
c= c= c = 3.0 x10c = 3.0 x1088
If either the frequency or wavelength If either the frequency or wavelength is known, the other can be calculatedis known, the other can be calculated
A red light has a wavelength of 728 *10A red light has a wavelength of 728 *10-9 -9
m. m.
What is the speed of the wave in What is the speed of the wave in m/s? m/s?
What is the frequency of the light?What is the frequency of the light?
A certain blue light has a frequency of 6.91 x 1014 Hz.
What is the wavelength of the light?
Determine the wave length of Determine the wave length of light with a speed of 50*10light with a speed of 50*106 6 Hz Hz
(/sec)(/sec)
If I have a wavelength of 780 If I have a wavelength of 780 *10*10-9-9 m and what is the m and what is the
frequency?frequency?
Microwave ovens often employ radiation with a frequency of 2.45 x 109 /s. What is the wavelength (in cm) of this radiation?
A purple light has a frequency of 7.42 A purple light has a frequency of 7.42 x 10x 101414 Hz. Hz. What is its wavelength? What is its wavelength? What is the energy of one quanta What is the energy of one quanta of of lightlight
300000000 m/s300000000 m/sNot just a good Not just a good
idea,idea,it’s the law!it’s the law!
Properties of Light
Form of energy,detectable with the eye,which can be transmitted fromone place to anotherat a finite velocity
Theory of Light
••Two complimentary theories to explain
how light behaves and the form bywhich it travels:
Particle Theory
Wave Theory
Particle Theory
• • Release of a photon
Electromagnetic spectrum and Electromagnetic spectrum and EnergyEnergy
longest
Planck’s Quantum Theory
In 1900, German Physicist Max Planck proposed:“Radiant energy may only be absorbed oremitted in discrete amounts: quanta.”
Electromagnetic spectrum and Electromagnetic spectrum and EnergyEnergy
Planck discovered the energy of a Planck discovered the energy of a wave or photon of light is constantwave or photon of light is constant
h = (6.63 x 10h = (6.63 x 10-34-34J/Hz)J/Hz)
Planck’s constant (h)Planck’s constant (h)
Energy and RadiationEnergy and Radiation
If the frequency of a wave is known, then the If the frequency of a wave is known, then the energy of the wave can be calculated as well in the energy of the wave can be calculated as well in the same mannersame manner
E=h E=h Or Or
E= h (c/E= h (c/))
Energy and RadiationEnergy and RadiationE=hvE=hv
Sample: What is the energy of a wave Sample: What is the energy of a wave which has a frequency of which has a frequency of 1.035 x 108 Hz?Hz?
h = 6.63 x10-34 J Hz = 1.035 x 108 Hz
6.86 x 106.86 x 10-26-26JJE = 6.63 x10-34 J
Hz
1.035 x 108 Hz=
PhotonsPhotons
Photons are a particle of radiation Photons are a particle of radiation or an individual or an individual quantumquantum of light of light
Quantum Quantum is a finite quantity of is a finite quantity of energy that can be gained or lost energy that can be gained or lost by an atomby an atom
The Nature of Light and The Nature of Light and RadiationRadiation
If eIf e-- are exposed to energy which are exposed to energy which matches those levels (matches those levels (a photona photon), ), they leap to unstable higher energy they leap to unstable higher energy levels.levels.
As they fall back they emit that energy As they fall back they emit that energy ( ( a photona photon) at a wavelength and ) at a wavelength and frequency which can be detected.frequency which can be detected.
http://www.olympusmicro.com/primer/java/fluorescence/exciteemit/
Photoelectric EffectPhotoelectric Effect
Albert Einstein proposed that light Albert Einstein proposed that light not only behaves as a wave, but as a not only behaves as a wave, but as a particle tooparticle too
Albert Einstein did not get the Nobel Albert Einstein did not get the Nobel Prize for Relativity. He received it for Prize for Relativity. He received it for work that he did between 1905 and work that he did between 1905 and 1911 on the Photoelectric Effect. 1911 on the Photoelectric Effect.
Photoelectric EffectPhotoelectric EffectIn 1905, Einstein applied this quantum
theory toexplain the photoelectric effect:
Photoelectric EffectPhotoelectric 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
e-e-e-
Einstein Photoelectric Effect
Ehv - Ee- = Ionization Energy
hv
e-
PhotoelectricPhotoelectric EffectEffect
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!
Photoelectric effectPhotoelectric effect
The reason that certain types of light The reason that certain types of light cause this effect but others do not has to cause this effect but others do not has to do with threshold energy do with threshold energy
Remember that electrons must gain Remember that electrons must gain energy in certain amounts (energy in certain amounts (E = hE = h))
Only certain types of light with “just the Only certain types of light with “just the right” frequency can cause electrons to right” frequency can cause electrons to become excitedbecome excited
The Nature of Light and The Nature of Light and RadiationRadiation
http://www.olympusmicro.com/primer/java/fluorescence/exciteemit/
Photoelectric EffectPhotoelectric Effect
View EMR as a collection of particles(called
photons), with each photon having the following energy:
E = hν
Photoelectric Effect 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
Photoelectric Effect Photoelectric Effect
Increased EMR intensity translates to an increase in the number of photons (increasing the number of electrons ejected)
EinsteinEinstein
Einstein did not Einstein did not receive his Nobel receive his Nobel Prize of the Prize of the theory of theory of relativity but for relativity but for his work on the his work on the photoelectric photoelectric effecteffect
Typed of SpectraTyped of Spectra
Hydrogen Line SpectrumHydrogen Line Spectrum
Because hydrogen atoms emit only Because hydrogen atoms emit only specific frequencies of light indicate specific frequencies of light indicate that the energy differenced between that the energy differenced between the atom states are fixedthe atom states are fixed
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
Light leads to ElectronsLight leads to Electrons
Electrons exist in specific, discrete levels Electrons exist in specific, discrete levels or or quantaquanta of energy of energy
The lowest energy of each electron is The lowest energy of each electron is known as its ground stateknown as its ground state
If the right amount (quantum) of energy is If the right amount (quantum) of energy is applied, then an electron will “leap” to applied, then an electron will “leap” to another energy levelanother energy level
The Bohr Atom
Each orbit corresponds to a particular energy
Orbit energies increase with increasing radii
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)
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
Bohr’s Bohr’s Model of H AtomModel of H Atom
Linked an atom’s Linked an atom’s e-e- to to photon emissionphoton emission Said that e’ can circle the nucleus only is Said that e’ can circle the nucleus only is
specific paths or specific paths or orbitsorbits.. Orbits are separated from the nucleus by Orbits are separated from the nucleus by
large empty spaces (large empty spaces (nodesnodes) where the e- ) where the e- cannot exist. (Rungs on a ladder)cannot exist. (Rungs on a ladder)
Remember, Remember, E increases as e- are furtherE increases as e- are further from the nucleusfrom the nucleus. .
Bohr’s Bohr’s Model of H AtomModel of H Atom While an e- is in orbit, it While an e- is in orbit, it cannot cannot gain nor gain nor
lose Elose E It It cancan, move to a higher E level , move to a higher E level IFIF it gains it gains
the amount of E = to the difference the amount of E = to the difference between the higher E orbit and the lower between the higher E orbit and the lower energy orbit.energy orbit.
When falls, it emits a When falls, it emits a PHOTON PHOTON = to the = to the difference.difference.
AbsorptionAbsorption gains E/ gains E/EmissionEmission gives off E gives off E
Take the good with the bad Take the good with the bad (Bohr’s Model)(Bohr’s Model)
Good:Good: Led scientists to believe a similar model Led scientists to believe a similar model
could be applied to all atoms.could be applied to all atoms.
Bad:Bad: Yikes!!! Did not explain the spectra of Yikes!!! Did not explain the spectra of
atoms with more than one e’ or atoms with more than one e’ or chemical behavior of atoms!chemical behavior of atoms!
The Bohr Model of the The Bohr Model of the AtomAtom
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!!!
The Nature of ElectronsThe Nature of Electrons
If light acts as both particles and If light acts as both particles and waves, then so do electrons.waves, then so do electrons.
If electrons act like waves, then how If electrons act like waves, then how can we locate them?can we locate them?
Atoms are like onions and Atoms are like onions and ogresogres
they have lots of layersthey have lots of layers
plantanswers.tamu.edu
Orbits Orbits We like to draw orbits as circularWe like to draw orbits as circular
but they really aren’tbut they really aren’t
OrbitsOrbits Turns out, there's no reason to Turns out, there's no reason to
assume that electron orbits are assume that electron orbits are circular. circular.
OrbitsOrbits
There are lots of paths an electron can There are lots of paths an electron can take in order to get around the nucleus.take in order to get around the nucleus.
(or through the nucleus)(or through the nucleus)
OrbitsOrbits
In fact it's very rare for an atom's electron In fact it's very rare for an atom's electron to be in a circular orbit. to be in a circular orbit.
Electron FactsElectron Facts
The electron moves at different speeds. The electron moves at different speeds. Fast near the nucleus and slow when it's Fast near the nucleus and slow when it's far from the nucleus. far from the nucleus.
Well we really don’tWell we really don’t
Because atoms are so small, no one Because atoms are so small, no one can see them. can see them.
For this reason, we just can't say For this reason, we just can't say exactly where the electron is, as it exactly where the electron is, as it moves about the nucleus. In those orbit moves about the nucleus. In those orbit pictures, we know the electron will be pictures, we know the electron will be somewhere on the white orbit lines. somewhere on the white orbit lines.
This makes the models involving This makes the models involving orbits, whether circles, or orbits, whether circles, or ellipses, wrong, because the ellipses, wrong, because the orbits are pretty specific about orbits are pretty specific about the electron's location. the electron's location.
So how do we locate electrons So how do we locate electrons in the modern atom?in the modern atom?
Quantum NumbersQuantum Numbers
Quantum NumbersQuantum Numbers
Specify the properties of Specify the properties of atomic orbitals and the atomic orbitals and the
properties of electrons in properties of electrons in orbitalorbital
Quantum NumbersQuantum Numbers
Don’t tell us where the electron is, Don’t tell us where the electron is, just where it's most likely to be. just where it's most likely to be.
The probable location of electrons The probable location of electrons are described using an address are described using an address
The four quantum numbersThe four quantum numbers
their symbols are n, l, m and s.their symbols are n, l, m and s.
EVERY electron in an atom has a EVERY electron in an atom has a specific,specific,
unique set of these four quantum unique set of these four quantum numbers.numbers.
Quantum NumbersQuantum Numbers
There are 4 parts to each addressThere are 4 parts to each address
Principle quantum number (Principle quantum number (nn)) Angular quantum number (Angular quantum number (ll)) Magnetic quantum number (Magnetic quantum number (mm)) Spin quantum number (Spin quantum number (ss))
The Principal Quantum The Principal Quantum Number Number
nnThe main energy level of an electronThe main energy level of an electron
Principal Quantum Principal Quantum NumberNumber ( (nn))
Describes the size of the orbital. Describes the size of the orbital.
Since the distance from of an electron Since the distance from of an electron from the nucleus is directly proportional from the nucleus is directly proportional to the energy of the electronto 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 …
Angular quantum number Angular quantum number ((ll))
AzimunthalAzimunthal Describes the shapeDescribes the shape
The secondary quantum number The secondary quantum number divides the shells into smaller groups divides the shells into smaller groups of orbitals called of orbitals called subshellssubshells ((sublevelssublevels). ).
s p d f g hs p d f g h......
Angular (Azimuthal) Angular (Azimuthal) Momentum Quantum NumberMomentum Quantum Number
LetterLetter ShapeShape
ss SphereSphere
pp DumbellDumbell
dd CloverleafCloverleaf
ff ““funky”funky”
Each suborbital can hold a maximum Each suborbital can hold a maximum of 2 electrons per orbitalof 2 electrons per orbital
Angular (Azimuthal) Angular (Azimuthal) Momentum Quantum NumberMomentum Quantum Number
LetterLetter Max Max number number
of of suborbitalsuborbital
ss
Max. # of Max. # of ee--
ss 11 22
pp 33 66
dd 55 1010
ff 77 1414
Quantum NumbersQuantum NumbersThe more crowded the dots are in a The more crowded the dots are in a
particular region, the better chance you particular region, the better chance you have to finding your electron there. have to finding your electron there.
s Orbitals Orbitalspheresphere
Orbitals of the same shape (s, for instance) grow larger as n increases…
Nodes are regions of low probability within an orbital.
Sizes of Sizes of ss orbitals orbitals
p Orbitalp Orbitaldumbbelldumbbell
two p Orbitalstwo p Orbitals
All three p OrbitalsAll three p Orbitals
d Orbitalsd OrbitalsCloverleafCloverleaf
orbital
f Orbitalsf Orbitals“funky”“funky”
orbital
Orbital filling tableOrbital filling table
The Magnetic Quantum The Magnetic Quantum Number Number
mm
describes the orientation in space of a describes the orientation in space of a particular orbital. particular orbital.
x, y, zx, y, z
Magnetic quantum Magnetic quantum number (number (mm))
The orientation in space The orientation in space What axis the orbit is located on What axis the orbit is located on
The Spin Quantum Number The Spin Quantum Number
ss
allows two electrons of opposite spin allows two electrons of opposite spin (or symmetry) into each orbital. (or symmetry) into each orbital.
+1/2 or -1/2+1/2 or -1/2
or or
Spin quantum number (Spin quantum number (ss) )
+1/2 -1/2
Aufbau (filling up) Aufbau (filling up) PrinciplePrinciple
the number of electrons in an atom is equal to the number of electrons in an atom is equal to the atomic numberthe atomic number
each added electron will enter the orbitals in each added electron will enter the orbitals in the order of increasing energythe order of increasing energy
an orbital can only hold 2 electrons. an orbital can only hold 2 electrons.
Hund’s RuleHund’s Rule
For orbitals of equal energy, one For orbitals of equal energy, one electron goes into each orbital until electron goes into each orbital until all orbitals are half-full.all orbitals are half-full.
1s2
2s2
2p4
Aufbau PrincipleAufbau Principle
Lower-energy orbitals of an atom are Lower-energy orbitals of an atom are filled with electrons first. filled with electrons first.
1s 2s 2p 3s 3p 4s 3d 4p …1s 2s 2p 3s 3p 4s 3d 4p …
Pauli Exclusion PrinciplePauli Exclusion Principle
No two electrons in an atom can No two electrons in an atom can have an identical set of four quantum have an identical set of four quantum numbers. (electrons sharing an numbers. (electrons sharing an orbital have different spins) orbital have different spins)
1s2
2s2
KeyKey Terms Terms Ground StateGround State Electron Configurations Electron Configurations
(1s(1s222s2s22…/…/Orbital NotationsOrbital Notations __ __ __ __ __ __ __ __ Aufbau PrincipleAufbau Principle (lowest first/periodic guide) (lowest first/periodic guide) Hund’s RuleHund’s Rule: Single e’ before pairing begins: Single e’ before pairing begins Pauli ExclusionPauli Exclusion (up/down—no 2 e’ same set of (up/down—no 2 e’ same set of
quant. #’s)quant. #’s) Highest Occupied LevelHighest Occupied Level Inner-Shell e’Inner-Shell e’ Noble Gas NotationNoble Gas Notation
Spin Spin Diagram Diagram
for for HydrogenHydrogen
Electron configuration for Hydrogen
1s1
Spin Spin Diagram Diagram
for for HeliumHelium
Electron configuration for Helium
1s2
Spin Spin Diagram Diagram
for for lithiumlithium
Electron configuration for lithium
1s22s1
Spin Spin Diagram Diagram
for for beryllium beryllium
Electron configuration for berylium
1s22s2
Spin Spin Diagram Diagram for boronfor boron
Electron configuration for boron
1s22s22p1
Spin Spin Diagram Diagram
for for carboncarbon
Electron configuration for carbon
1s22s22p2
Spin Spin Diagram Diagram
for for nitrogennitrogen
Electron configuration for nitrogen
1s22s22p3
Spin Spin Diagram Diagram
for for oxygenoxygen
Electron configuration for oxygen
1s22s22p4
Spin Spin Diagram Diagram
for for fluorinefluorine
Electron configuration for fluorine
1s22s22p5
Spin Spin Diagram Diagram for neonfor neon
Electron configuration for neon
1s22s22p6
Standard Standard NotationNotation
or Complete or Complete electron electron
configuration configuration of Fluorineof Fluorine
Main Energy
Level
Numbers
1, 2, 2Sublevels
Number of electrons in the sub level 2,2,5
1s2 2s2 2p5
Shorthand Notation orShorthand Notation orNoble Gas ConfiguraitonNoble Gas Configuraiton
Use the last noble gas that is located Use the last noble gas that is located in the periodic table right before the in the periodic table right before the element.element.
Write the symbol of the noble gas in Write the symbol of the noble gas in brackets.brackets.
Write the remaining configuration Write the remaining configuration after the brackets.after the brackets.
Ex: Fluorine: [He] 2Ex: Fluorine: [He] 2ss22 2 2pp55
Blocks in the Periodic Table
You broke your big toe! The x ray You broke your big toe! The x ray they take of toe uses waves that they take of toe uses waves that have a length 2.19 x 10have a length 2.19 x 101010m.m. What is the speed of the wave in What is the speed of the wave in m/s?m/s? What is the wavelength in nm? What is the wavelength in nm? What is the frequency of the x What is the frequency of the x ray? ray?