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:

http://www.lpscience.fatcow.com/mgagnon/Photoelectric_Effect/photoelectriceffect1.htm

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?