Chapter 5Chapter 5Electronic StructureElectronic Structure

Light Through a PrismLight Through a Prism• White light (sunlight) is a blend of all colors (ROY G BIV)White light (sunlight) is a blend of all colors (ROY G BIV)

combined together.combined together.

• The wavelength (The wavelength (λλ) and frequency () and frequency (υυ) for each color are unique to) for each color are unique tothat color.that color.

• As light passes through a prism…As light passes through a prism… - the different wavelengths of the colors are separated.- the different wavelengths of the colors are separated. - individual colors can be detected by the eye.- individual colors can be detected by the eye. - a rainbow appears.- a rainbow appears.

The Electromagnetic The Electromagnetic SpectrumSpectrum

• All substancesAll substances (radioactive or not) emit electromagnetic radiation. (radioactive or not) emit electromagnetic radiation.

light:light:• Only part of the spectrum that human eyes can detect is visibleOnly part of the spectrum that human eyes can detect is visible

((RROOYY GG BBIIVV))• All other radiations have wavelengths that are either too long orAll other radiations have wavelengths that are either too long or

too short for our eyes to detect.too short for our eyes to detect.

• The Electromagnetic Spectrum (EM spectrum) is made of the different forms of electromagnetic waves and is based on the frequency and wavelength of the wave. EM waves do not require a medium to travel…..

Cosmic rays

Microwaves

Increasing danger

too long to seetoo long to seetoo short to seetoo short to see

7.4 x 107.4 x 10-6-6 m mlongestlongest

4.2 x 104.2 x 10-6-6 m mshortestshortest

•The followingThe following list [A to G] list [A to G] namesnames the forms of the forms of the EM spectrumthe EM spectrum in order of energy, in order of energy, frequency and wavelengthfrequency and wavelength.. [A…..largest wavelength, [A…..largest wavelength, lowest frequency & lowest energy] lowest frequency & lowest energy]

A . A . radio wavesradio waves (includes AM, FM, (includes AM, FM, TV, radar, shortwaves)TV, radar, shortwaves) used for used for communicationcommunicationBB. . microwavesmicrowaves -- -- used in cooking; can used in cooking; can penetrate air, glass, paper and plasticpenetrate air, glass, paper and plastic

C. C. infraredinfrared (heating lamps)(heating lamps) felt as warmthfelt as warmth;; used to keep food warmused to keep food warm

D. D. visiblevisible (only portion that humans (only portion that humans can see; smallest part of the spectrum)can see; smallest part of the spectrum) ROY G. BIVROY G. BIV…violet has the greatest …violet has the greatest energy, frequency, and smallest energy, frequency, and smallest wavelength of all the colorswavelength of all the colors

E. E. ultravioletultraviolet (causes sunburn) (causes sunburn)

F.x-rays (medical use) will pass through the human body with the exception of some bones and tissues

G. gamma rays (treatment of cancer ) can kill living cells

[[GG…..…..smallest wavelength, highest smallest wavelength, highest frequency & highest energyfrequency & highest energy]]

Wavelength vs. Wavelength vs. FrequencyFrequency

• Wavelength (λ): distance b/n crests of a wave.Wavelength (λ): distance b/n crests of a wave.

WavelengthWavelength

crestcrest

troughtroughWavelengthWavelength

long wavelengthlong wavelength

short wavelengthshort wavelength

*** higher frequency = higher energy ****** higher frequency = higher energy ***

• Frequency (ν): # of wavelengths that pass a certain point in aFrequency (ν): # of wavelengths that pass a certain point in agiven amount of time.given amount of time.

- units are Hertz (Hz)- units are Hertz (Hz)

• These 2 waves are traveling at = speeds…These 2 waves are traveling at = speeds…

which wave will havewhich wave will havemore crests cross the ‘finish line’ in a matter of one min.?more crests cross the ‘finish line’ in a matter of one min.?

FIN

ISH

low frequencylow frequency

high frequencyhigh frequency = short wavelength= short wavelength

= long wavelength= long wavelength

Wave CalculationsWave Calculations

• wavelength (wavelength (λλ)) and frequency ( and frequency (υυ)) are inversely related. are inversely related.

• all waves on the EM spectrum travel at the speed of light (c).all waves on the EM spectrum travel at the speed of light (c).

c = λ(ν)c = λ(ν)

• c = speed of light = 3.00 x 10c = speed of light = 3.00 x 1088 m/s. m/s.

• to solve for to solve for λλ … …

νννν

c c

λλ == νν• to solve for to solve for υυ … …

c c

νν ==λλ

λλλλ

• Practice…Practice…

Calculate the Calculate the υυ of a wave that has a wavelength of 5.00 x 10 of a wave that has a wavelength of 5.00 x 10-6-6 m. m.

c c

νν ==λλ νν ==

3.00 x 103.00 x 1088 5.00 x 105.00 x 10-6-6

νν 6.00 x 106.00 x 101313

Hz Hz

==

What is the What is the λλ of radiation with a frequency of 1.50 x 10 of radiation with a frequency of 1.50 x 101313 Hz? Hz?

c c

λλ == νν λλ ==3.00 x 103.00 x 1088 1.50 x 101.50 x 101313

λλ == 2.00 x 102.00 x 10-5-5

m m

Does this radiation have a shorter or longer Does this radiation have a shorter or longer λλ than red light? than red light?longerlonger……red light ~ 7.4 x 10red light ~ 7.4 x 10-6-6 m m

• Max Planck explained that light is emitted in packets (quanta) Max Planck explained that light is emitted in packets (quanta) called ‘photons’ which are distinct bundles of energy.called ‘photons’ which are distinct bundles of energy.

• Planck also assumed that energy of a photon is directlyPlanck also assumed that energy of a photon is directlyproportional to the frequency of the light.proportional to the frequency of the light.

E = h(ν)E = h(ν)

• E = energy (in Joules)E = energy (in Joules)• υυ = frequency = frequency• hh = Planck’s constant (6.626 x 10 = Planck’s constant (6.626 x 10-34-34 J/Hz) J/Hz)

• Practice…Practice…

• Calculate the energy of radiation with a Calculate the energy of radiation with a υυ of 5.00 x 10 of 5.00 x 101515 Hz. Hz.

E = h(ν)E = h(ν) E = 6.626 x 10E = 6.626 x 10-34 -34 (5.00 x 10(5.00 x 101515)) E =E = 3.31 x 103.31 x 10-18 -18 JJ

ννhhhh == EE

hh

Obj. 5…Atomic SpectraObj. 5…Atomic Spectra• all elements will emit light when excited (i.e. by electricity). all elements will emit light when excited (i.e. by electricity).

• atoms absorb energy and then emit an = amount of energy in theatoms absorb energy and then emit an = amount of energy in theform of light.form of light.

- atoms emit a characteristic color- atoms emit a characteristic color- Ne = orange - red- Ne = orange - red- Na = bright yellow- Na = bright yellow

• if we pass this light through a prism (separate the if we pass this light through a prism (separate the λλ) we get an) we get anatomic emission spectrum.atomic emission spectrum.

ex. of wavelengths emittedex. of wavelengths emittedset-upset-up

Obj. 5 cont…Obj. 5 cont…• emission spectra are unique to particular elements. emission spectra are unique to particular elements.

• only show certain lines of the continuous spectrum (white light). only show certain lines of the continuous spectrum (white light).

• have helped us gather a lot of info. about our universe! have helped us gather a lot of info. about our universe!

• atomic absorption spectraatomic absorption spectra shows colors missing from the shows colors missing from thecontinuous spectrum (missing continuous spectrum (missing λλ were absorbed by the element). were absorbed by the element).

continuous continuous

absorption absorption

emissionemission

Obj. 6-7…How Atoms Obj. 6-7…How Atoms Absorb and Emit EnergyAbsorb and Emit Energy• e- are found on certain e- are found on certain energy levelsenergy levels (orbitals) around the atom. (orbitals) around the atom.

- there is a maximum of seven energy levels in an atom.- there is a maximum of seven energy levels in an atom.

- an e- an e- - requires one ‘quanta’ of energy to jump to the nextrequires one ‘quanta’ of energy to jump to the nextenergy level.energy level.

- e- on the energy level closest to the nucleus have the lowest- e- on the energy level closest to the nucleus have the lowestenergy. The 7energy. The 7thth energy level has the highest energy. energy level has the highest energy.

• e- at their lowest energy level are considered to be at thee- at their lowest energy level are considered to be at theground stateground state (most stable). (most stable).• if e- absorb a quantum or more of energy (from electricity), theyif e- absorb a quantum or more of energy (from electricity), they

can jump to higher energy levels (can jump to higher energy levels (excited stateexcited state).).• e- must lose energy in order to fall from the excited state back toe- must lose energy in order to fall from the excited state back to

the ground state.the ground state.- this energy is emitted in the form of visible light!- this energy is emitted in the form of visible light!

Obj. 6-7 cont…Obj. 6-7 cont…

• ‘‘Heinsburg’s uncertainty principle’ Heinsburg’s uncertainty principle’ states that it is impossible tostates that it is impossible to

know exactly where an e- is, b/c it is constantly in motion.know exactly where an e- is, b/c it is constantly in motion.