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Electron EnergiesElectron Energies

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Electromagnetic SpectrumElectromagnetic Spectrum

Electromagnetic radiation is a form of Electromagnetic radiation is a form of energy that exhibits wave-like behavior as energy that exhibits wave-like behavior as it travels though space. it travels though space.

EM radiation is organized into a spectrum EM radiation is organized into a spectrum according to wavelength ( ) and frequency according to wavelength ( ) and frequency (v) of the waves. (v) of the waves.

The spectrum includes the areas; radio The spectrum includes the areas; radio waves, infrared, visible light, ultraviolet, x-waves, infrared, visible light, ultraviolet, x-rays, and gamma rays.rays, and gamma rays.

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Mathematical RelationshipsMathematical Relationships

Wavelength and frequency are inversely Wavelength and frequency are inversely proportional. As one increases, the other proportional. As one increases, the other decreases.decreases.

The speed of EM waves is related to The speed of EM waves is related to wavelength and frequency in the following wavelength and frequency in the following way. c = vway. c = v

Because the speed of light is constant, it is Because the speed of light is constant, it is possible to conclude that wavelength and possible to conclude that wavelength and frequency are inversely proportional.frequency are inversely proportional.

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PhotonsPhotons

All areas on the electromagnetic spectrum All areas on the electromagnetic spectrum carry particles of electromagnetic radiation carry particles of electromagnetic radiation called photons. called photons.

A photon has zero mass but carries a A photon has zero mass but carries a quantum of energyquantum of energy..

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QuantaQuanta

This minimum energy contained by the This minimum energy contained by the photon is called quantum energy.photon is called quantum energy.

This quantum energy is determined by the This quantum energy is determined by the frequency of the radiation carried by the frequency of the radiation carried by the photon. photon. E = E = hvhv

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PlanckPlanck

It was Planck who discovered that all It was Planck who discovered that all energy comes in these packets of quanta.energy comes in these packets of quanta.

He was able to prove photons of quantum He was able to prove photons of quantum energy existed by observing the energy existed by observing the photoelectric effect.photoelectric effect.

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Photoelectric EffectPhotoelectric Effect

When light shines on metal, photons in the When light shines on metal, photons in the light can knock electron’s off of the atoms light can knock electron’s off of the atoms in the metal.in the metal.

This only occurs if the photon that hits the This only occurs if the photon that hits the metal has at least the minimum energy metal has at least the minimum energy required to knock the electron loose. required to knock the electron loose.

Therefore, matter absorbs only whole Therefore, matter absorbs only whole numbers of photons of EM energy.numbers of photons of EM energy.

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Jumping ElectronsJumping Electrons

Photons not only knock electrons lose from Photons not only knock electrons lose from an atom, they can also be absorbed or an atom, they can also be absorbed or released from an atom.released from an atom.

Photons of energy can be absorbed by Photons of energy can be absorbed by electrons in an atom causing the atom to be electrons in an atom causing the atom to be at an excited state. at an excited state.

Photons can also be released by electrons Photons can also be released by electrons in an atom causing the atom to be at ground in an atom causing the atom to be at ground state.state.

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Orbital EnergyOrbital Energy

When current is passes through a gas at low When current is passes through a gas at low pressure, the atoms within the gas become pressure, the atoms within the gas become excited.excited.

As an electron falls from the excited state to the As an electron falls from the excited state to the ground state, energy is given off in the form of a ground state, energy is given off in the form of a photon of radiation.photon of radiation.

The energy of the photon is equal to the The energy of the photon is equal to the difference in energy between the two orbits.difference in energy between the two orbits.

Ephoton = E2 - E1Ephoton = E2 - E1

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Emission/absorption SpectraEmission/absorption Spectra

The released photon of radiation can be The released photon of radiation can be sent through a prism where it becomes sent through a prism where it becomes separated into its specific frequencies, separated into its specific frequencies, forming a line-emission spectrum.forming a line-emission spectrum.

The color and position of the light on the The color and position of the light on the emission spectrum relate to the emission spectrum relate to the wavelength and frequency of the photon wavelength and frequency of the photon and therefore its quantum energy.and therefore its quantum energy.

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Continuous or Line SpectraContinuous or Line Spectra

Because they originally thought atoms would Because they originally thought atoms would become excited by any amount of energy added, become excited by any amount of energy added, it was thought this spectrum would be it was thought this spectrum would be continuous.continuous.

Instead the spectrum that was produced had Instead the spectrum that was produced had only lines of distinct frequencies.only lines of distinct frequencies.

This indicated that only fixed amounts of energy, This indicated that only fixed amounts of energy, quanta, were being released or absorbed as quanta, were being released or absorbed as electrons moved between orbits.electrons moved between orbits.

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Quantized Energy LevelsQuantized Energy Levels

This fixed line spectrum suggested that This fixed line spectrum suggested that energy differences between the atom’s energy differences between the atom’s energy states were also fixed. energy states were also fixed.

These set energy levels were named These set energy levels were named orbits. orbits.

The energy of the orbits increases with The energy of the orbits increases with increasing distance from the nucleus.increasing distance from the nucleus.

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Bohr Atomic ModelBohr Atomic Model Bohr proposed a hydrogen atom model that links Bohr proposed a hydrogen atom model that links

the atom’s single electron with its photon line the atom’s single electron with its photon line emission spectrum.emission spectrum.

Bohr found the wavelength from the radiation’s Bohr found the wavelength from the radiation’s frequency on the line emission spectrum.frequency on the line emission spectrum.

Using the wavelength, he calculated the Using the wavelength, he calculated the energies that an electron must have to have at energies that an electron must have to have at each energy level.each energy level.

This technique allowed him to model the This technique allowed him to model the hydrogen atom correctly, but doesn’t work very hydrogen atom correctly, but doesn’t work very well with atoms containing more than one well with atoms containing more than one electron.electron.

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Particle/Wave DualityParticle/Wave Duality

It was already known that electrons It was already known that electrons exhibited particle like qualities. exhibited particle like qualities.

However, the fact that electrons confined However, the fact that electrons confined to orbits produce only certain frequencies, to orbits produce only certain frequencies, they were exhibiting wave like properties they were exhibiting wave like properties as well.as well.

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De BroglieDe BroglieDe Broglie found more evidence for the De Broglie found more evidence for the

wave like properties of electronswave like properties of electronsElectrons interact with one another just as Electrons interact with one another just as

waves do.waves do.They diffract/bend as they pass by the They diffract/bend as they pass by the

edge of an object.edge of an object.They can interfere with one another, They can interfere with one another,

producing areas of constructive and producing areas of constructive and destructive interference.destructive interference.

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Quantum TheoryQuantum Theory

Quantum theory mathematically describes Quantum theory mathematically describes the wave properties of very small objects the wave properties of very small objects such as electrons.such as electrons.

It has become the leading branch of It has become the leading branch of physics that deals with atomic and physics that deals with atomic and subatomic systems subatomic systems

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OrbitalsOrbitals

Based on Heisenberg’s principle, only the Based on Heisenberg’s principle, only the probability of the location of an electron can be probability of the location of an electron can be determined.determined.

Therefore, Bohr’s theory of neat orbits was Therefore, Bohr’s theory of neat orbits was thrown out.thrown out.

Instead, it is now thought that electrons orbit the Instead, it is now thought that electrons orbit the nucleus in three dimensional regions called nucleus in three dimensional regions called orbitals.orbitals.

The orbital give the probable location of an The orbital give the probable location of an electron.electron.

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Heisenberg Uncertainty PrincipleHeisenberg Uncertainty Principle

Electrons are detected by their interaction with Electrons are detected by their interaction with photons. But any attempt to locate an electron photons. But any attempt to locate an electron with a photon knocks the electron off its course. with a photon knocks the electron off its course.

As a result there is a basic uncertainty in trying As a result there is a basic uncertainty in trying to locate an electron. to locate an electron.

Heisenberg’s principle states that it is impossible Heisenberg’s principle states that it is impossible to determine the position and speed of an to determine the position and speed of an electron at the same time. electron at the same time.

Although difficult for scientists to accept, it has Although difficult for scientists to accept, it has become one of the fundamental principles of our become one of the fundamental principles of our present understanding of light and matter.present understanding of light and matter.

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Quantum NumbersQuantum Numbers

Quantum numbers Quantum numbers describe the properties describe the properties of orbits and the electrons within the of orbits and the electrons within the orbits.orbits.

Using these, it is possible to figure out why Using these, it is possible to figure out why each orbit contains its specified amount of each orbit contains its specified amount of electrons.electrons.

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Principle Quantum NumberPrinciple Quantum Number

The principle quantum number, n, gives The principle quantum number, n, gives the main energy level occupied by the the main energy level occupied by the electron. electron.

Electrons that share the same main Electrons that share the same main energy level are said to be in the same energy level are said to be in the same shell.shell.

n=1n=1 11stst shell shelln=2n=2 22ndnd shell shelln=3n=3 33rdrd shell shell

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Angular Momentum Quantum Angular Momentum Quantum NumberNumber

Angular momentum quantum number, L, Angular momentum quantum number, L, indicates the sublevels in the main shell. indicates the sublevels in the main shell.

L values are zero and all numbers less L values are zero and all numbers less than n. than n.

The L values correspond to certain shapes The L values correspond to certain shapes of orbits.of orbits.

0 = 0 = s-shapeds-shaped and spherical and spherical1 = p-shaped and dumbbell shaped1 = p-shaped and dumbbell shaped2 = d-shaped and cross shaped2 = d-shaped and cross shaped

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Magnetic Quantum NumberMagnetic Quantum Number Magnetic quantum number, m, gives the Magnetic quantum number, m, gives the

orientation of an orbital around a nucleus.orientation of an orbital around a nucleus. s = 1 orientations = 1 orientation

p = 3 orientationsp = 3 orientationsd = 5 orientationsd = 5 orientations

The total number of orbitals within each shell is The total number of orbitals within each shell is nn22..

Each orientation of an orbital can hold two Each orientation of an orbital can hold two electrons. electrons.

Therefore the total number of electrons per shell Therefore the total number of electrons per shell is 2nis 2n22..

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Spin Quantum NumberSpin Quantum Number

Spin quantum number indicates the spin of Spin quantum number indicates the spin of the electrons in each orbitthe electrons in each orbit

The spin of electrons in the same orbit The spin of electrons in the same orbit must be opposites.must be opposites.

The two values of these spins are + ½ and The two values of these spins are + ½ and – ½. – ½.

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Electron Configuration NotationElectron Configuration Notation

Gives the main energy levels and Gives the main energy levels and sublevels of the element.sublevels of the element.

The number of electrons in each sublevel The number of electrons in each sublevel is also shown in superscript. is also shown in superscript.

You start at 1s and continue filling up until You start at 1s and continue filling up until the correct number of electrons are used.the correct number of electrons are used.

1s1s222s2s222p2p66…………

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Noble Gas NotationNoble Gas Notation

This shortened version of electron This shortened version of electron configuration allows noble gas symbols to configuration allows noble gas symbols to represent part of the configuration.represent part of the configuration.

The noble gas that occurs before the The noble gas that occurs before the element on the periodic table is the one element on the periodic table is the one used. used.

Only the Only the notationnotation after that noble gas has after that noble gas has to be written. to be written.

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Orbital NotationOrbital Notation

In this notation, an In this notation, an orbital orbital is represented is represented by a line with the main level and sublevel by a line with the main level and sublevel written underneath it.written underneath it.

Arrows showing electrons and their spin is Arrows showing electrons and their spin is written above the line. Each line can only written above the line. Each line can only hold two electrons. hold two electrons.

It is necessary to write the notation for the It is necessary to write the notation for the level as may times as there is orientations level as may times as there is orientations for that level.for that level.

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Three PrinciplesThree Principles There are three principles that must be There are three principles that must be

followed when writing electron configurations followed when writing electron configurations and orbital notations.and orbital notations.

Aufbau principle- an electrons occupies the Aufbau principle- an electrons occupies the lowest-energy orbital it can.lowest-energy orbital it can.

Pauli exclusion principle- no two electrons in Pauli exclusion principle- no two electrons in the same orbit can have the same spin the same orbit can have the same spin quantum number.quantum number.

Hund’s rule- orbitals of equal energy must Hund’s rule- orbitals of equal energy must each have one electron before any is allowed each have one electron before any is allowed to have a second.to have a second.

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