atomic structure and periodicity. atoms protonsneutronselectrons 1. where are the electrons 2. do...
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AtomsAtoms
ProtonsProtons
NeutronsNeutrons
ElectronsElectrons
1. Where are the electrons1. Where are the electrons
2. Do they have different energies2. Do they have different energies
Electromagnetic Electromagnetic RadiationRadiation
Radiant energy that exhibits Radiant energy that exhibits wavelength-like behavior and wavelength-like behavior and travels through space at the speed travels through space at the speed of light in a vacuum.of light in a vacuum.
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10-12 10-10 10-8 4 x 10-7
Gammarays
X rays Ultraviolet Infrared Microwaves Radio waves
FM Shortwave AM
4 x 10-7
Wavelength in meters
5 x 10-7 6 x 10-7 7 x 10-7
7 x 10-7 10-4 10-2 1 102 104
Vis
ible
WavesWaves
Waves have 3 primary characteristics:Waves have 3 primary characteristics:
1.1. WavelengthWavelength: distance between two peaks : distance between two peaks in a wave.in a wave.
2.2. FrequencyFrequency: number of waves per second : number of waves per second that pass a given point in space.that pass a given point in space.
3.3. SpeedSpeed: speed of light is 2.9979 : speed of light is 2.9979 10 1088 m/s. m/s.
07_93 1 second
= 4 cycles/second = 4 hertz
= 8 cycles/second = 8 hertz
= 16 cycles/second = 16 hertz
Wavelength and frequency can be interconverted.Wavelength and frequency can be interconverted.
= = cc// = frequency (s= frequency (s11))
= wavelength (m)= wavelength (m)
cc = speed of light (m s = speed of light (m s11))
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10-12 10-10 10-8 4 x 10-7
Gammarays
X rays Ultraviolet Infrared Microwaves Radio waves
FM Shortwave AM
4 x 10-7
Wavelength in meters
5 x 10-7 6 x 10-7 7 x 10-7
7 x 10-7 10-4 10-2 1 102 104
Vis
ible
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Unplucked string
1 half-wavelength
2 half-wavelengths
3 half-wavelengths
Standing Waves
Quantization in Nature
Planck’s ConstantPlanck’s Constant
EE = change in energy, in J = change in energy, in J
hh = Planck’s constant, 6.626 = Planck’s constant, 6.626 10 103434 J s J s
= frequency, in s= frequency, in s11
= wavelength, in m= wavelength, in m
E hhc
= =
Transfer of energy is quantized, and can only Transfer of energy is quantized, and can only occur in discrete units, called quanta.occur in discrete units, called quanta.
Energy and MassEnergy and Mass
Energy has massEnergy has mass
EE = = mmcc22
EE = energy = energy
mm = mass = mass
cc = speed of light = speed of light
Energy and MassEnergy and Mass
Ehc
photon =
mhcphoton =
(Hence the (Hence the dualdual nature of light.) nature of light.)
Wavelength and MassWavelength and Mass
= wavelength, in m= wavelength, in m
hh = Planck’s constant, 6.626 = Planck’s constant, 6.626 10 103434 J s = kg m J s = kg m22 s s11
mm = mass, in kg = mass, in kg
= frequency, in s= frequency, in s11
= h
m
de Broglie’s Equationde Broglie’s Equation
Atomic Spectrum of HydrogenAtomic Spectrum of Hydrogen
Continuous spectrumContinuous spectrum: Contains : Contains allall the the wavelengths of light.wavelengths of light.
Line (discrete) spectrumLine (discrete) spectrum: Contains : Contains only only some some of the wavelengths of light.of the wavelengths of light.
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Prism
Slit
Continuousspectrum
Electric arc(white lightsource)
(a)
Prism
Slit
Detector(photographic plate)
Hydrogen gas
(b)
Highvoltage
410 nm 434 nm 486 nm 656 nm
Detector(photographic plate)
Arc
V I B G Y O R
+
-
+
-
The Bohr ModelThe Bohr Model
EE = energy of the levels in the H-atom = energy of the levels in the H-atom
z z = nuclear charge (for H, = nuclear charge (for H, zz = 1) = 1)
nn = an integer = an integer
E = 2.178 10 J (18 2 z n/ )2
The electron in a hydrogen atom moves around the The electron in a hydrogen atom moves around the nucleus only in certain allowed circular orbits.nucleus only in certain allowed circular orbits.
The Bohr ModelThe Bohr Model
Ground StateGround State: The lowest : The lowest possible energy state for an possible energy state for an atom (atom (nn = 1). = 1).
Energy Changes in the Energy Changes in the Hydrogen AtomHydrogen Atom
EE = = EEfinal statefinal state EEinitial stateinitial state
= hcE
Quantum MechanicsQuantum Mechanics
Based on the Based on the wave properties wave properties of the atomof the atom
= wave function= wave function
= mathematical operator= mathematical operator
EE = total energy of the atom = total energy of the atom
A specific wave function is often called an A specific wave function is often called an orbitalorbital..
H E =
H
Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple
x mvh
4
xx = position = position
mvmv = momentum = momentum
hh = Planck’s constant = Planck’s constant
The more accurately we know a particle’s The more accurately we know a particle’s position, the less accurately we can know its position, the less accurately we can know its momentum.momentum.
Probability DistributionProbability Distribution
- square of the wave functionsquare of the wave function
- probabilityprobability of finding an electron at a of finding an electron at a given positiongiven position
RadialRadial probability distribution is the probability distribution is the probability distribution in each spherical probability distribution in each spherical shell.shell.
Quantum Numbers (QN)Quantum Numbers (QN)
1.1. Principal QN Principal QN ((nn = 1, 2, 3, . . .) - related to = 1, 2, 3, . . .) - related to sizesize and and energyenergy of the orbital. of the orbital.
2.2. Angular Momentum QN Angular Momentum QN ((ll = 0 to = 0 to nn 1) - relates to 1) - relates to shapeshape of the orbital. of the orbital.
3.3. Magnetic QN Magnetic QN ((mmll = l to = l to l) - relates to l) - relates to orientationorientation
of the orbital in space relative to other orbitals.of the orbital in space relative to other orbitals.
4.4. Electron Spin QN Electron Spin QN ((mmss = += +11//22, , 11//22) - relates to the ) - relates to the
spin states spin states of the electrons.of the electrons.
Pauli Exclusion PrinciplePauli Exclusion Principle
In a given atom, no two electrons can have In a given atom, no two electrons can have the same set of four quantum numbers (the same set of four quantum numbers (nn, , ll, , mmll, , mmss).).
ThereforeTherefore, an orbital can hold only two , an orbital can hold only two electrons, and they must have opposite electrons, and they must have opposite spins.spins.
Aufbau PrincipleAufbau Principle
As protons are added one by one As protons are added one by one to the nucleus to build up the to the nucleus to build up the elements, electrons are similarly elements, electrons are similarly added to these hydrogen-like added to these hydrogen-like orbitals.orbitals.
Hund’s RuleHund’s Rule
The lowest energy configuration The lowest energy configuration for an atom is the one having the for an atom is the one having the maximum number of unpaired maximum number of unpaired electrons electrons allowed by the Pauli allowed by the Pauli principle in a particular set of principle in a particular set of degenerate orbitals.degenerate orbitals.
Valence ElectronsValence Electrons
Atom Valence Electrons
Ca 2
N 5
Br 7
The electrons in the outermost principle The electrons in the outermost principle quantum level of an atom.quantum level of an atom.
Inner electrons are called Inner electrons are called corecore electrons. electrons.
Broad Periodic Table Broad Periodic Table ClassificationsClassifications
Representative Elements Representative Elements (main group): (main group): filling filling ss and and pp orbitals (Na, Al, Ne, O) orbitals (Na, Al, Ne, O)
Transition ElementsTransition Elements: filling : filling dd orbitals (Fe, orbitals (Fe, Co, Ni)Co, Ni)
Lanthanide and Actinide Series Lanthanide and Actinide Series (inner (inner transition elements): filling transition elements): filling 44ff and and 55ff orbitals (Eu, Am, Es)orbitals (Eu, Am, Es)
Ionization EnergyIonization Energy
The quantity of energy The quantity of energy required to remove an electron required to remove an electron from the gaseous atom or ion.from the gaseous atom or ion.
Periodic TrendsPeriodic Trends
First ionization energyFirst ionization energy: :
increases increases from left to right across from left to right across a a periodperiod;;
decreasesdecreases going down a going down a groupgroup..
Electron AffinityElectron Affinity
The energy change associated The energy change associated with the addition of an electron to with the addition of an electron to a gaseous a gaseous atomatom..
X(X(gg) + e) + e X X((gg))
Periodic TrendsPeriodic Trends
Atomic RadiiAtomic Radii::
decreasedecrease going from left to right going from left to right across a across a periodperiod;;
increase increase going down a going down a groupgroup..
Information Contained in the Information Contained in the Periodic TablePeriodic Table
1.1. Each group member has the same valence electron Each group member has the same valence electron configuration (these electrons primarily determine an configuration (these electrons primarily determine an atom’s chemistry).atom’s chemistry).
2.2. The electron configuration of any representative The electron configuration of any representative element.element.
3.3. Certain groups have special names (alkali metals, Certain groups have special names (alkali metals, halogens, etc).halogens, etc).
4.4. Metals and nonmetals are characterized by their Metals and nonmetals are characterized by their chemical and physical properties.chemical and physical properties.