Development of Development of Atomic ModelsAtomic Models

DemocritusDemocritus Greek philosopher Greek philosopher

400 BC400 BC

QuestionQuestion

Is there a limit to Is there a limit to the number of the number of times matter could times matter could be divided? be divided?

Democritus TheoryDemocritus Theory Eventually, you would Eventually, you would

reach a piece that was reach a piece that was “indivisible”“indivisible”

Named this smallest Named this smallest piece of matter piece of matter “atomos,”“atomos,” meaning “not to be cut.”meaning “not to be cut.”

AtomosAtomos

Small, hard particles.Small, hard particles.

Differ in shape and size Differ in shape and size for each substancefor each substance

Aristotle and PlatoAristotle and Plato

All matter made up of combination of earth, fire, air and water.

Aristotle

The Four Elements??The Four Elements??

This concept influenced This concept influenced early chemists called early chemists called alchemistsalchemists..

Buried in HistoryBuried in History

““AtomosAtomos”” theory was theory was ignored and forgotten ignored and forgotten for more than for more than 2000 2000 years!years!

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

Performed careful scientific Performed careful scientific experiments. experiments.

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

Dalton’s Atomic TheoryDalton’s Atomic Theory

Matter is made of tiny Matter is made of tiny indivisible particles indivisible particles called atoms.called atoms.

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

Dalton’s Atomic TheoryDalton’s Atomic Theory CompoundsCompounds are atoms of are atoms of

different elements combined different elements combined in in fixed proportions.fixed proportions.

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

Atoms cannot be created or Atoms cannot be created or destroyed, but are destroyed, but are conserved.conserved.

Pages from Dalton’s JournalPages from Dalton’s Journal

Hard SpheresHard Spheres

Dalton’s model is called the Dalton’s model is called the ““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 ray shows how ray behaved in a behaved in a magnetic field.magnetic field.

Cathode Rays were Cathode Rays were negatively chargednegatively charged

Cathode Rays were Cathode Rays were particlesparticles

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JJ is AwesomeJJ is AwesomeConcluded the

negative “cathode ray” particles came from within atoms.

Discovered the first Discovered the first subatomic particle subatomic particle (electron).(electron).

What about the Positive?What about the Positive?

But…matter is But…matter is neutralneutral..

Must be a positive Must be a positive chargecharge in the atom to in the atom to balance the negative.balance the negative.

Plum Pudding ModelPlum Pudding Model

Positively charged Positively charged sphere with with sphere with with negatively charged negatively charged particles scattered particles scattered throughout.throughout.

Yummy…Yummy…

Ernest Rutherford (1908)Ernest Rutherford (1908)

Physicist who Physicist who worked with the worked with the new field of new field of radioactive radioactive emissions.emissions.

Different Types of RadiationDifferent Types of Radiation

Used a Used a magnetic fieldmagnetic field to to determine there were determine there were three types of radiation.three types of radiation.

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

Charges of RadiationCharges of RadiationThe radiation had different charges.The radiation had different charges.

Identify the charge each type of radiation has.

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

These particles have These particles have aa positive charge positive charge

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

Gold Foil ExperimentGold Foil Experiment

Observation:Observation:Almost all alpha particles passed straightAlmost all alpha particles passed straightthrough the gold foil.through the gold foil.

Conclusion:Conclusion:Most of the atom’s volume is empty space.Most of the atom’s volume is empty space.

Observation:Observation: A few alpha particles were deflected at an A few alpha particles were deflected at an

angle or bounced back.angle or bounced back.

Conclusion:Conclusion: Atoms have a very small, dense positively Atoms have a very small, dense positively

charged nucleus.charged nucleus.

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

Deflections happened rarely (1/8000).Deflections happened rarely (1/8000).

The Nuclear ModelThe Nuclear ModelRutherford’s Model is

called the

“Nuclear Model”

Comparison to ThomsonComparison to Thomson Positively charge Positively charge

contained in nucleus. contained in nucleus.

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

Not dispursed evenly.Not dispursed evenly.

http://chemmovies.unl.edu/ChemAnime/Rhttp://chemmovies.unl.edu/ChemAnime/RUTHERFD/RUTHERFD.htmlUTHERFD/RUTHERFD.html

http://chemmovies.unl.edu/ChemAnime/Rhttp://chemmovies.unl.edu/ChemAnime/RUTHERFD/RUTHERFD.htmlUTHERFD/RUTHERFD.html

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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 LevelsDifferent 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 = = the total number of electrons the total number of electrons an energy level can an energy level can

hold.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 AtomEx: 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?

Draw a Bohr IonDraw a Bohr IonThey 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)(+) ions are smaller(+) ions are smaller

Lost electron(s)Lost electron(s)

(-) Ions (anions)(-) Ions (anions)(-) ions are larger(-) ions are larger

Gained electron(s)Gained electron(s)

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

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

What are Spectral Lines?What are Spectral Lines? Energy gets absorbed by an atom causing it to Energy gets absorbed by an atom causing it to

emit a emit a unique setunique set of colored lines. of colored lines.

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

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

http://www.mhhe.com/physsci/chemistry/esshttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swfentialchemistry/flash/linesp16.swf

What Causes Spectral Lines?What Causes Spectral Lines?

Jumping Electrons!!Jumping Electrons!!

Jumping ElectronsJumping Electrons Electrons normally exist in the lowest energy Electrons normally exist in the lowest energy

level possible called the level possible called the ““ground stateground state”. (stable)”. (stable)

““Ground state” eGround state” e-- configurations are written on the configurations are written on the periodic table for each element.periodic table for each element.

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

An Electron Gets “Excited”An Electron Gets “Excited”Electrons can Electrons can absorbabsorb a photon of energy and a photon of energy and ““jump upjump up”” to a higher energy level farther from the to a higher energy level farther from the nucleus.nucleus.

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

Jumping ElectronsJumping ElectronsThey quickly They quickly ““fall back downfall back down”” to the to the

ground stateground state.. (stable) (stable)

They They emitemit a photon of energy that a photon of energy that corresponds to how far they jumped.corresponds to how far they jumped.

This photon of energy is seen as a This photon of energy is seen as a spectral line!spectral line!

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.

REMEMBERREMEMBER

Absorb EnergyAbsorb EnergyJump UpJump Up

Emit EnergyEmit EnergyFall DownFall Down

Electromagnetic SpectrumElectromagnetic Spectrum

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

Lines of visible colors Lines of visible colors make up only a small make up only a small part of the spectrum.part of 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?

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

Calculating the Energy of a Calculating the Energy of a Spectral LineSpectral Line

STEP 1:

If you know the wavelength of the spectral line you can find it’s frequency.

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

λ = wavelength (in meters)

ү = frequency of the wave

Calculating the Energy of a Calculating the Energy of a Spectral LineSpectral Line

STEP 2:STEP 2:

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

E = h x E = h x ү

E = energy in Joules

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

ү = frequency of the wave

Electron Cloud Model

Electron Cloud ModelElectron Cloud Model

Sometimes called:Sometimes called: Wave Mechanical Model Wave Mechanical Model Quantum Mechanical ModelQuantum Mechanical Model Orbital ModelOrbital Model Charge Cloud ModelCharge Cloud Model

How is it Different from the How is it Different from the Planetary Model?Planetary Model?

Heisenberg’s Uncertainty Heisenberg’s Uncertainty Principle:Principle:It is It is impossibleimpossible to know the to know the exact location and momentum of exact location and momentum of an electron at the same time.an electron at the same time.

We can’t tell exactly where an We can’t tell exactly where an electron is!!electron is!!

Electrons exist in Electrons exist in ““orbital cloudsorbital clouds””

The denser the The denser the region of the cloud region of the cloud the the higher thehigher the probabilityprobability of finding of finding an electron there.an electron there.

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How are Electrons Organized?How are Electrons Organized?

Electron Electron HotelHotel

Energy Levels (1-7)Energy Levels (1-7)Electrons can be at different distances Electrons can be at different distances

from the nucleus.from the nucleus.

Energy Levels Energy Levels 11 22 33 4 4 5 5 6 6 7 7

Lowest energyLowest energy Highest energyHighest energyClosest to nucleusClosest to nucleus Farthest from NucleusFarthest from Nucleus

Sublevels (s, p, d, f)Sublevels (s, p, d, f) Each energy level can have a certain number of Each energy level can have a certain number of

sublevels.sublevels.

Energy LevelEnergy Level Sublevels PossibleSublevels Possible11 ss22 s, ps, p33 s, p, ds, p, d44 s, p, d, fs, p, d, f55 s, p, d, f, (g)s, p, d, f, (g)66 s, p, d, f, (g, h)s, p, d, f, (g, h)77 s, p, d, f, (g, h, i)s, p, d, f, (g, h, i)

Energy of SublevelsEnergy of SublevelsSublevels have different levels of energy.Sublevels have different levels of energy.

ss pp dd ffLowest energyLowest energy Highest energyHighest energy

Orbitals in SublevelsOrbitals in Sublevels Each sublevel contains a different number of orbitals.Each sublevel contains a different number of orbitals.

A A maximum of two electronsmaximum of two electrons can exist in an orbital. can exist in an orbital.

SublevelSublevel # of Orbitals# of Orbitals Max eMax e-- in Sublevel in Sublevel ss 11 2 2 ee--

pp 33 6 6 ee--

dd 55 10 10 ee--

ff 77 14 14 ee--

Electron SpinElectron Spin Pauli Exclusion PrinciplePauli Exclusion Principle::

In order for two electrons to In order for two electrons to occupy the same orbital, they occupy the same orbital, they must have opposite spins.must have opposite spins.

Electrons in an orbital Electrons in an orbital spinspin in opposite directionsin opposite directions

Shapes of OrbitalsShapes of Orbitals

Orbitals come in different shapes and Orbitals come in different shapes and sizes.sizes.

They are the They are the region of highest probabilityregion of highest probability of finding an electron.of finding an electron.

s Orbitals Orbital

Probability cloud has a spherical shapeProbability cloud has a spherical shape

p Orbitals (pp Orbitals (pxx, p, pyy, p, pzz))

““Dumbell” Dumbell” shapeshape

Three p orbitals can exist, on the x, y, z axis in space

d Orbitalsd Orbitals

Five possible d orbitals existFive possible d orbitals exist

f Orbitalsf Orbitals

Seven possible f orbitals existSeven possible f orbitals exist