The Quantum Model of the The Quantum Model of the Atom Part 1Atom Part 1

Electrons as WavesElectrons as Waves

The Word for the day is…The Word for the day is… Quantized-Quantized-

Only certain specific values are allowed.Only certain specific values are allowed.

The electron’s energy is The electron’s energy is quantized. quantized. This This means that it can only have certain specific means that it can only have certain specific amounts of energy at a given timeamounts of energy at a given time

QuantizedQuantized What if the accelerator on your car was What if the accelerator on your car was

quantized?quantized? Is it?Is it?

What do you think?

Your fingerprint Your fingerprint looks like thislooks like this

An Elements An Elements fingerprint looks like fingerprint looks like thisthis

Atomic Emission SpectrumAtomic Emission Spectrum

We need someone who We need someone who could make a could make a connection between connection between the atomic emission the atomic emission spectrum of an element spectrum of an element and the model of an and the model of an atomatom

And his name wasAnd his name was

– BohrBohr

–Neils BohrNeils Bohr

How did Bohr’s model explain the How did Bohr’s model explain the bright line spectrum produced by bright line spectrum produced by

hydrogen?hydrogen? When the atom When the atom absorbsabsorbs energy the electron energy the electron

“jumps”“jumps” to a to a higher energy levelhigher energy level (orbit). (orbit). When the electron When the electron “falls”“falls” to a lower orbit the to a lower orbit the

energy is releasedenergy is released as a photon of light. as a photon of light. Remember a Remember a photonphoton is a particle of light is a particle of light The color of light produced corresponds to The color of light produced corresponds to

the size of the energy change.the size of the energy change. Remember this equation: Remember this equation:

E = hfE = hf

What type of spectrum is produced What type of spectrum is produced when hydrogen emits light and why?when hydrogen emits light and why?

A bright line or atomic emission spectrum is A bright line or atomic emission spectrum is produced … NOT a continuous spectrumproduced … NOT a continuous spectrum

The electron’s energy levels are The electron’s energy levels are quantized, quantized, the energy levels increase by specific the energy levels increase by specific certain amounts of energycertain amounts of energy..

Electrons can only Electrons can only absorbabsorb or or releaserelease certain certain specific amounts of energyspecific amounts of energy. Thus…. Thus…

……only certain specific colors, frequencies or only certain specific colors, frequencies or photons (energies) of light can be produced!photons (energies) of light can be produced!

So how did Bohr change the Planetary So how did Bohr change the Planetary model (Rutherford’s model) to make it model (Rutherford’s model) to make it better?better?

Lets take a look!!Lets take a look!!

Bohr Model of the AtomBohr Model of the Atom

Notice thatthe electronis changingenergy levels!!

How does the photon that is emitted (the How does the photon that is emitted (the released energy) correspond to the released energy) correspond to the colored lines we see in the atomic colored lines we see in the atomic emission spectrum? emission spectrum?

Lets look again at Hydrogen Lets look again at Hydrogen

Atomic Emission SpectrumOf Hydrogen

RememberRemember

Excited hydrogen atoms emit a pinkishglow. When the Visible portion of theemitted light is passed through a prism, it is separated into specific wavelengths that are part of hydrogen’s line-emission spectrum.

Why are only certain specific colors Why are only certain specific colors produced?produced?

Because the electron can only have certain Because the electron can only have certain specific amounts of potential energy. In specific amounts of potential energy. In other words, it is other words, it is quantizedquantized!!

Thus, the electron can only absorb or Thus, the electron can only absorb or release certain specific amounts of energy…release certain specific amounts of energy…corresponding to the specific colors in it’s corresponding to the specific colors in it’s atomic emission spectrum.atomic emission spectrum.

HOMEWORKHOMEWORK

Pg 118 # 8,9Pg 118 # 8,9

What is the relationship between ROYGBIV What is the relationship between ROYGBIV and the ENERGY CHANGE???and the ENERGY CHANGE???

Quiz class after nextQuiz class after next

What did Bohr’s Model Give UsWhat did Bohr’s Model Give Us Three important idea’s:Three important idea’s:

1 – Electron’s exist in stable orbits about the 1 – Electron’s exist in stable orbits about the nucleusnucleus

2 – Only certain orbits are allowed2 – Only certain orbits are allowed

3 – An electron must absorb and emit an 3 – An electron must absorb and emit an quantity of energy that is equal to the energy quantity of energy that is equal to the energy change between the two levels. change between the two levels.

What were the shortcomings of Bohr’s model of the atom?

• Scientists did not understand why the electron could only exist in certain specific orbits or energy levels? (quantized)

•It worked perfectly for hydrogen (1 electron) but not for the other elements.

Section 4-2Section 4-2

The ?????? Model of the AtomThe ?????? Model of the Atom

Matter WavesMatter Waves

-The wave-like behavior of particles -The wave-like behavior of particles (electrons)(electrons)

de Broglie Hypothesisde Broglie Hypothesis states that states that any moving any moving particle or object has an associated waveparticle or object has an associated wave . .

For this he won the Nobel Prize in Physics in For this he won the Nobel Prize in Physics in 19291929

Tiny electrons behave similar to wavesTiny electrons behave similar to waves When confined to a space, waves can only have When confined to a space, waves can only have

certain frequencies (energies). Thus, they are certain frequencies (energies). Thus, they are quantized like electrons in Bohr’s model.quantized like electrons in Bohr’s model.

Light has a dual (particle/wave) nature. The Light has a dual (particle/wave) nature. The electron has a dual (particle/wave) nature as well.electron has a dual (particle/wave) nature as well.

Louis de BroglieLouis de Broglie

De Broglie wavelength equationDe Broglie wavelength equation

An electron that has a mass of 9.11 x 10An electron that has a mass of 9.11 x 10 -28-28 g is g is traveling at 90 mi/hrtraveling at 90 mi/hr– It has a wavelength of 2 x 10It has a wavelength of 2 x 10-5-5 m measured in the IR m measured in the IR

sectionsection

A baseball that has a mass of 0.15 kg that is A baseball that has a mass of 0.15 kg that is pitched at 90 mi/hrpitched at 90 mi/hr– It has a wavelength of 1.1 x 10It has a wavelength of 1.1 x 10-34-34 m, not measurable by m, not measurable by

any instrumentany instrument

Every object has wave propertiesEvery object has wave propertiesh

mv

Lets take a look at the Double Slit Lets take a look at the Double Slit ExperimentExperiment

http://www.youtube.com/watch?v=DfPeprQ7oGc

Heisenberg’s Uncertainty PrincipleHeisenberg’s Uncertainty Principle

It is impossible to determine simultaneously It is impossible to determine simultaneously the position and velocity of an electron or the position and velocity of an electron or any other particle.any other particle.

This is due to the fact that by observing an This is due to the fact that by observing an electron, the measurement itself will cause electron, the measurement itself will cause the electron to change position. Light will the electron to change position. Light will interact with an electron and cause it to interact with an electron and cause it to move.move.

The way around this problem is to describe The way around this problem is to describe electron location in terms of probability of electron location in terms of probability of finding the electron in certain regions in the finding the electron in certain regions in the atom.atom.

Werner Heisenberg is speeding down a highway, Werner Heisenberg is speeding down a highway, when he's pulled over by the police. The cop walks when he's pulled over by the police. The cop walks up to him and says, "Excuse me, sir, do you know up to him and says, "Excuse me, sir, do you know how fast you were driving?" how fast you were driving?"

Heisenberg looks up to theHeisenberg looks up to the

officer and says, officer and says,

"Nope, but I know "Nope, but I know

exactlyexactly where where

I was!" I was!"

SchrSchrÖÖdinger’s Wave Equationdinger’s Wave Equation

2 2 2 2

2 2 2 2

8, , , , 0

mE V x y z x y z

x y z h

Memorize this equation

Just Kidding

SchrSchrÖÖdinger’s Wave Equationdinger’s Wave Equation

Equation describes the wave properties of Equation describes the wave properties of electrons and other small particles.electrons and other small particles.

Proved quantizationProved quantization– Only waves of specific energies and therefore Only waves of specific energies and therefore

frequencies provide solutions to the equationfrequencies provide solutions to the equation

Describes the arrangement of electrons in Describes the arrangement of electrons in atoms.atoms.

Together, the ideas that electrons Together, the ideas that electrons are quantized, the de Broglie wave are quantized, the de Broglie wave

properties, the Heisenberg properties, the Heisenberg uncertainty principle and the addition uncertainty principle and the addition

of the Schrödinger wave equation of the Schrödinger wave equation laid the foundation for the laid the foundation for the

development of the quantum-development of the quantum-mechanical model of an atom.mechanical model of an atom.

The modern electron cloud model The modern electron cloud model (a.k.a. quantum-mechanical model) (a.k.a. quantum-mechanical model) shows electrons orbiting around the shows electrons orbiting around the

nucleus in specific regions (or nucleus in specific regions (or “clouds”) based on the probability “clouds”) based on the probability of finding them within that region.of finding them within that region.

Yet again another modification Yet again another modification to the atomic modelto the atomic model

Lets take a look backLets take a look back

HomeworkHomework

Read pg 98 – 100Read pg 98 – 100

Answer question #10 on page 118Answer question #10 on page 118

Answer question: What is the Heisenberg Answer question: What is the Heisenberg Uncertainty Principle??Uncertainty Principle??

OrbitalsOrbitals ORBITAL ORBITAL ≠ ORBIT≠ ORBIT

A three dimensional region around the A three dimensional region around the nucleus that indicates the most probable nucleus that indicates the most probable location of an electron with a given energy.location of an electron with a given energy.– Higher probability – higher electron densityHigher probability – higher electron density– Lower probability – lower electron densityLower probability – lower electron density

There are several different types of orbitals There are several different types of orbitals each having a different fundamental shape.each having a different fundamental shape.

http://www.winter.group.shef.ac.uk/orbitron/AOs/3d/index.html

The 5 d orbitals

HomeworkHomework

Read pg. 101-104Read pg. 101-104

Questions 1-3 on pg 104Questions 1-3 on pg 104