Development of Development of Atomic ModelsAtomic Models

DemocritusDemocritus

Greek philosopher Greek philosopher

400 BC400 BC

““Atomos” conceptAtomos” concept

Can matter can be Can matter can be divided forever? divided forever?

Eventually, a piece Eventually, a piece would be would be “indivisible”“indivisible”

““Atomos,”Atomos,” meaning “not meaning “not to be cut,” is smallest to be cut,” is smallest piece of matterpiece of matter

John Dalton (early 1800’s)John Dalton (early 1800’s)

Coined the term “atom”.Coined the term “atom”.

Dalton’s Atomic TheoryDalton’s Atomic Theory

Matter made of tiny Matter made of tiny indivisible particles indivisible particles called “atoms”.called “atoms”.

Atoms of one element Atoms of one element are alike, and different are alike, and different from atoms of other from atoms of other elements. elements.

Page from Dalton’s JournalPage from Dalton’s Journal

Dalton’s Theory Continued…Dalton’s Theory Continued…

Compounds form when Compounds form when different atoms combine in different atoms combine in fixed fixed proportions.proportions.

Chemical reactions involve Chemical reactions involve rearrangement of atoms.rearrangement of atoms.

Atoms can’t be created or Atoms can’t be created or destroyed, but are destroyed, but are conserved in conserved in chemical reactions.chemical reactions.

Dalton’s Atomic Theory calledDalton’s Atomic Theory called

““Hard Spheres Model”Hard Spheres Model”

JJ Thomson (1897)JJ Thomson (1897)

Thomson’ ExperimentsThomson’ Experiments

Studied Studied “cathode “cathode raysrays” (electric current) ” (electric current) in a “Crooke’s Tube”.in a “Crooke’s Tube”.

Fluorescent screen, Fluorescent screen, shows how cathode shows how cathode ray behaved in a ray behaved in a magnetic field.magnetic field.

Lets draw a typical Crooke’s Tube in our notes.

Cathode Rays were Cathode Rays were negatively chargednegatively charged

They bent toward (+) plate

Cathode Ray Tube and Magnethttp://youtu.be/XU8nMKkzbT8

Cathode Rays were Cathode Rays were particlesparticles

They couldn’t pass through matter.

JJ is AwesomeJJ is Awesome

Concluded the negative “cathode ray” particles came from within atoms.

Discovered first Discovered first subatomic particle subatomic particle ((electronelectron).).

What about the Positive?What about the Positive?

But…matter is But…matter is neutralneutral..

Therefore: Therefore: A positive charge

must exist to balance must exist to balance the negative.the negative.

Plum Pudding ModelPlum Pudding Model

Atoms are positively charged spheres with Atoms are positively charged spheres with negatively charged particles scattered throughout.negatively charged particles scattered throughout.

Yummy…Yummy…

Brian Cox: Thompson and Discovery of Electronhttp://youtu.be/IdTxGJjA4Jw

Ernest Rutherford (1908)Ernest Rutherford (1908)

Physicist who Physicist who worked in new field worked in new field of radioactivity. of radioactivity.

Found 3 Different Types of Found 3 Different Types of RadiationRadiation

Used Used magnetic fieldmagnetic field to to isolate three types of isolate three types of radiation.radiation.

Alpha (Alpha (αα) ) Beta (Beta (ββ)) Gamma (Gamma (γγ))

Charges of RadiationCharges of Radiation

The radiation had different charges.The radiation had different charges.

Identify the charge each type of radiation has.

Shot Shot alpha particlesalpha particles, , at very thin piece of at very thin piece of gold foil.gold foil.

Alpha particles have a Alpha particles have a positive chargepositive charge, and a , and a mass of 4 amumass of 4 amu

Fluorescent screenFluorescent screen shows where the shows where the particles went.particles went.

Gold Foil ExperimentGold Foil Experiment

Rutherford Gold Foilhttp://www.youtube.com/watch?v=5pZj0u_XMbc

Observation:Observation:

Most alpha particles passed straightMost alpha particles passed straight

through gold foil.through gold foil.

Conclusion:Conclusion:

Atom’s volume is mostly empty space.Atom’s volume is mostly empty space.

Observation:Observation:

A few alpha particlesA few alpha particles

deflected at an angledeflected at an angle

or bounced back.or bounced back.

Conclusion:Conclusion:

Atoms have a veryAtoms have a very

small, dense positivelysmall, dense positively

charged nucleus.charged nucleus.

http://www.kentchemistry.com/moviesfiles/Units/AtomicStructure/Rutherford3.htm

Modern Example of Gold Foil Experiment in Actionhttp://youtu.be/XBqHkraf8iE

Nucleus is extremely small compared to the size of the atom as a whole.

Deflections happened rarely (1/8000).

The Nuclear ModelThe Nuclear Model

Rutherford’s Model is called the “Nuclear Model”

Brian Cox: Rutherford and the Nucleushttp://youtu.be/wzALbzTdnc8

Comparison to ThomsonComparison to Thomson

Positively charge only Positively charge only contained in nucleus. contained in nucleus.

Negatively particles Negatively particles scattered outside scattered outside nucleus.nucleus.

Charge is not Charge is not disbursed evenly.disbursed evenly.

Niels Bohr (1913)Niels Bohr (1913)

Came up with the Came up with the ““Planetary ModelPlanetary Model””

Bohr’s TheoryBohr’s Theory

Electrons circle nucleus Electrons circle nucleus in specific in specific energy levelsenergy levels or “shells”.or “shells”.

The higher the “energy The higher the “energy level,” the higher the level,” the higher the electron’s energy.electron’s energy.

Energy LevelsEnergy Levels

Different energy levels can contain Different energy levels can contain different numbers of electrons.different numbers of electrons.

How many per level?How many per level?

n = the number of the energy leveln = the number of the energy level

2n2n22 = = maximum number of electrons maximum number of electrons

an energy level can hold. an energy level can hold.

Ex: Level 3 can hold 2(3)Ex: Level 3 can hold 2(3)22 = 18 electrons = 18 electrons

Draw a Bohr AtomDraw a Bohr Atom

Ex: The Fluorine Atom (F)Ex: The Fluorine Atom (F)Protons = 9Protons = 9Neutrons = 10Neutrons = 10Electrons = 9Electrons = 9

How many energy levels do you draw?How many energy levels do you draw?How many electrons in each level?How many electrons in each level?

Human Bohr Modelhttp://www.youtube.com/watch?v=PLpZfJ4rGts

Draw a Bohr IonDraw a Bohr Ion

They only difference is that one or more They only difference is that one or more electrons gets added or taken out of the electrons gets added or taken out of the outer energy level.outer energy level.

Ex: The Magnesium Ion (MgEx: The Magnesium Ion (Mg+2+2))Protons = 12Protons = 12Neutrons = 12Neutrons = 12Electrons = 10Electrons = 10

(+) Ions (cations)(+) Ions (cations)are smallerare smaller

Lost electron(s)Lost electron(s)

(-) Ions (anions)(-) Ions (anions)are largerare larger

Gained electron(s)Gained electron(s)

How Did Bohr Come Up With His How Did Bohr Come Up With His Model?Model?

Studied Studied spectral linesspectral lines emitted by various emitted by various elements (especially Hydrogen)elements (especially Hydrogen)

What are Spectral Lines?What are Spectral Lines?

Energy absorbed by an atom causes it to emit a Energy absorbed by an atom causes it to emit a unique setunique set of colored lines. of colored lines.

Used to identify elements present in a sample. Used to identify elements present in a sample. (elemental “Fingerprint”)(elemental “Fingerprint”)

Spectral Lines are Different for Spectral Lines are Different for Each ElementEach Element

Answer: 1

What Causes Spectral Lines?What Causes Spectral Lines?

Jumping Electrons!!Jumping Electrons!!

Video of Line Spectra of Hydrogenhttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swf

Jumping ElectronsJumping Electrons

Electrons normally exist in lowest energy level Electrons normally exist in lowest energy level possible called possible called ““ground stateground state”. (stable)”. (stable)

““Ground state” eGround state” e-- configurations are written on configurations are written on periodic tableperiodic table

Ex: Ex: Aluminum is 2-8-3Aluminum is 2-8-3

Calcium is 2-8-8-2Calcium is 2-8-8-2

An Electron Gets “Excited”An Electron Gets “Excited”Electrons Electrons absorbabsorb a photon (or “quanta”) of energy a photon (or “quanta”) of energy and and ““jump upjump up”” to a higher energy level farther to a higher energy level farther from nucleus.from nucleus.

This is called This is called ““excited stateexcited state”. ”. (unstable)(unstable)

Jumping ElectronsJumping ElectronsElectrons quickly Electrons quickly ““fall back downfall back down”” to to

ground stateground state.. (stable) (stable)They They emitemit a photon (or “quanta”) of energy a photon (or “quanta”) of energy

that corresponds to how far they jumped.that corresponds to how far they jumped.

Each spectral line corresponds to a Each spectral line corresponds to a specific specific photonphoton of energy that is released. of energy that is released.

Model Of Hydrogen Atom and Electrons JumpingModel Of Hydrogen Atom and Electrons Jumping

http://www.upscale.utoronto.ca/PVB/Harrison/BohrModel/Flash/BohrModel.htmlhttp://www.upscale.utoronto.ca/PVB/Harrison/BohrModel/Flash/BohrModel.html

REMEMBERREMEMBER

Absorb EnergyAbsorb Energy

Jump UpJump Up

Emit EnergyEmit Energy

Fall DownFall Down

Excited vs Ground StateExcited vs Ground State Periodic table lists ground state electron Periodic table lists ground state electron

configurations for neutral atoms.configurations for neutral atoms.To recognize an “excited state” configuration, To recognize an “excited state” configuration,

count the electrons and see if the configuration count the electrons and see if the configuration matches the one on the table.matches the one on the table.

Ex: 2-8-7-3 = 20 electronsEx: 2-8-7-3 = 20 electronsCalcium (atomic # 20) is 2-8-8-2Calcium (atomic # 20) is 2-8-8-2So this must be showing one of the ways calcium So this must be showing one of the ways calcium

could be in the excited state.could be in the excited state.

Valence ElectronsValence Electrons

Electrons in highest occupied energy level.Electrons in highest occupied energy level. Involved in forming bonds with other atoms.Involved in forming bonds with other atoms.Atoms are most stable when they have a Atoms are most stable when they have a

“stable octet” of 8 valence electrons“stable octet” of 8 valence electrons

Noble Gases: (Group 18) Noble Gases: (Group 18) ““Inert” and unreactive (have stable octet)Inert” and unreactive (have stable octet)

Ex: Ex: ArgonArgon 2-8-8, 2-8-8, Neon 2-8Neon 2-8

Valence ElectronsValence Electrons

Look at last number in atom’s electron Look at last number in atom’s electron configuration to determine number of configuration to determine number of valence electrons.valence electrons.

Ex: Ex: AlAl 2-8-32-8-3 3 valence3 valenceCaCa 2-8-8-22-8-8-2 2 valence2 valenceFF 2-72-7 7 valence7 valence

Lewis Dot DiagramsLewis Dot Diagrams

Shows number of Shows number of valence electrons valence electrons an an atom has as “dots” around atom’s symbol.atom has as “dots” around atom’s symbol.

Phosphorus is 2-8-5

KernelKernel

Nucleus and non-valence electrons Nucleus and non-valence electrons Inner part of atom not involved directly in Inner part of atom not involved directly in

reactionsreactions

Ex: Ex: Al Al 2-8-32-8-3 has 10 kernel electronshas 10 kernel electrons

and 3 valence and 3 valence electronselectrons

The Nature of LightThe Nature of Light

Study of light has provided important information about the Study of light has provided important information about the structure of atoms. structure of atoms.

Dual Nature of LightDual Nature of Light: : behaves as behaves as both waves and as particlesboth waves and as particles (depending on (depending on

what type of experiment is being performed.)what type of experiment is being performed.)

Speed of LightSpeed of Light: all light waves travel at the same velocity : all light waves travel at the same velocity C = 3.0 x 10C = 3.0 x 1088 meters/sec meters/sec

What is Light?What is Light? https://www.youtube.com/watch?v=eCVPhjHh57Ehttps://www.youtube.com/watch?v=eCVPhjHh57E Greatest Discovery in Physics: (Duality of Light)Greatest Discovery in Physics: (Duality of Light) https://www.youtube.com/watch?v=XB-iLRsq8A8https://www.youtube.com/watch?v=XB-iLRsq8A8

Electromagnetic SpectrumElectromagnetic Spectrum

Spectral lines can Spectral lines can come from all areas come from all areas of EM Spectrum.of EM Spectrum.

Visible colors make Visible colors make up only a small part of up only a small part of the spectrum.the spectrum.

EM waves carry different amounts of energy EM waves carry different amounts of energy based upon their based upon their wavelengthwavelength and and frequencyfrequency..

Which wave has higher energy?

Wavelength (λ): distance between two peaks of a wave

Frequency (γ): number of peaks that pass per second. (Hertz (Hz) or cycles/sec)

Relationship of Frequency, Wavelength and Energy of colored linehttp://employees.oneonta.edu/viningwj/sims/plancks_equation_s.html

Calculating the Energy of a Calculating the Energy of a Spectral Line (HONORS)Spectral Line (HONORS)

STEP 1:

Given wavelength of spectral line find it’s frequency.

c = λ x ү

c = the speed of light = 3 x 108 meters/sec

λ = wavelength (in meters)

1 x 10-9 meter = 1 nm 1 x 10-10 meter = 1 Angstrom

ү = frequency of the wave (Hertz or waves/sec, s-1)

Calculating the Energy of a Calculating the Energy of a Spectral Line (HONORS)Spectral Line (HONORS)

STEP 2:STEP 2:

Using frequency find energy of the line (in Joules)Using frequency find energy of the line (in Joules)

E = h x E = h x ү

E = energy (Joules)

h = Planck's constant = 6.63 × 10-34 kg x m2 / sec

ү = frequency of the wave (Hertz or waves/sec, s-1)

Calculating Energy for Specific Calculating Energy for Specific Jumps Between Energy LevelsJumps Between Energy Levels

(For Hydrogen)(For Hydrogen)

∆ ∆ E = EE = Efinal final - E- EInitialInitial

-2.180 x 10-2.180 x 10-18-18 J/e- J/e- - - -2.180 x 10-2.180 x 10-18-18 J/e- J/e-

nn22 nn22

Final Energy levelFinal Energy level Initial Energy levelInitial Energy level

Honors Good Overview VideoHonors Good Overview Video

What is Light: Lecture on Photon emission and absorbtion (2 hours)What is Light: Lecture on Photon emission and absorbtion (2 hours) https://www.youtube.com/watch?v=axUkUuj6aushttps://www.youtube.com/watch?v=axUkUuj6aus