chapter 71 atomic structure chapter 7. 2 electromagnetic radiation -visible light is a small portion...
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Chapter 7 1
Atomic StructureAtomic Structure
Chapter 7Chapter 7
Chapter 7 2
Electromagnetic RadiationElectromagnetic Radiation
- Visible light is a small portion of the electromagnetic spectrum
Chapter 7 3
Frequency (v, nu – The number of times per second that one complete wavelength passes a given point.
Wavelength (lambda) – The distance between identical points on successive waves.
v = c
c = speed of light, 2.997 x 108 m/s
Electromagnetic RadiationElectromagnetic Radiation
Chapter 7 4
- When talking about atomic structure, a special type of wave is important:
Standing Wave: A special type of wave with two or more stationary point with no amplitude.
Electromagnetic RadiationElectromagnetic Radiation
Chapter 7 5
- We can also say that light energy is quantized- This is used to explain the light given-off by hot
objects. - Max Planck theorized that energy released or
absorbed by an atom is in the form of “chunks” of light (quanta).
E = h vh = planck’s constant, 6.63 x 10-34J/s
- Energy must be in packets of (hv), 2(hv), 3(hv), etc.
Planck, Einstein, Energy and PhotonsPlanck, Einstein, Energy and Photons
Planck’s EquationPlanck’s Equation
Chapter 7 6
Planck, Einstein, Energy and PhotonsPlanck, Einstein, Energy and Photons
The Photoelectric EffectThe Photoelectric Effect
Chapter 7 7
The Photoelectric EffectThe Photoelectric Effect- The photoelectric effect provides evidence for the
particle nature of light.- It also provides evidence for quantization.- If light shines on the surface of a metal, there is a
point at which electrons are ejected from the metal.- The electrons will only be ejected once the
threshold frequency is reached .- Below the threshold frequency, no electrons are
ejected.- Above the threshold frequency, the number of
electrons ejected depend on the intensity of the light.
Planck, Einstein, Energy and PhotonsPlanck, Einstein, Energy and Photons
Chapter 7 8
The Photoelectric EffectThe Photoelectric Effect
- Einstein assumed that light traveled in energy packets called photons.
- The energy of one photon, E = h.
Planck, Einstein, Energy and PhotonsPlanck, Einstein, Energy and Photons
Chapter 7 9
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Line SpectraLine Spectra
Chapter 7 10
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Line SpectraLine Spectra
Chapter 7 11
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Line SpectraLine Spectra
Line spectra can be “explained” by the following equation:
- this is called the Rydberg equation for hydrogen.
21
22
18 1110179.2
1
nnx
Chapter 7 12
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Bohr’s ModelBohr’s Model- Assumed that a single electron moves around the
nucleus in a circular orbit. - The energy of a given electron is assumed to be
restricted to a certain value which corresponds to a given orbit.
k = 2.179 x 10-18J z = atomic numbern = integer for the orbit
2
2
n
kzE
Chapter 7 13
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Bohr’s ModelBohr’s Model- Assumed that a single electron moves around the
nucleus in a circular orbit. - The energy of a given electron is assumed to be
restricted to a certain value which corresponds to a given orbit.
n = integer for the orbit ao = 0.0529 angstroms z = atomic number
z
anradius o
2
Chapter 7 14
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Bohr’s Model – Important FeaturesBohr’s Model – Important Features- Quantitized energy and angular momentum- The first orbit in the Bohr model has n = 1 and is
closest to the nucleus.- The furthest orbit in the Bohr model has n close to
infinity and corresponds to zero energy.- Electrons in the Bohr model can only move between
orbits by absorbing and emitting energy in quanta (h).
Chapter 7 15
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Bohr’s Model – Line SpectraBohr’s Model – Line Spectra
Ground State – When an electron is in its lowest energy orbit.
Excited State – When an electron gains energy from an outside source and moves to a higher energy orbit.
Chapter 7 16
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Bohr’s Model – Line SpectraBohr’s Model – Line Spectra
12)( EElightE
Chapter 7 17
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Bohr’s Model – Line SpectraBohr’s Model – Line Spectra
21
2
22
2
12)(
n
kz
n
kz
EElightE
Chapter 7 18
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Bohr’s Model – Line SpectraBohr’s Model – Line Spectra
21
22
2
21
2
22
2
12
11
)(
nnkz
n
kz
n
kz
EElightE
Chapter 7 19
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Bohr’s Model – Line SpectraBohr’s Model – Line Spectra
21
22
18
21
22
2
21
2
22
2
12
1110179.2
11
)(
nnx
nnkz
n
kz
n
kz
EElightE
Chapter 7 20
Bohr’s Model of the Hydrogen Atom Bohr’s Model of the Hydrogen Atom
Bohr’s ModelBohr’s Model- Since the energy states are quantized, the light emitted
from excited atoms must be quantized and appear as line spectra.
Chapter 7 21
Quantum Mechanical View of the AtomQuantum Mechanical View of the Atom- DeBroglie proposed that there is a wave/particle
duality.- Knowing that light has a particle nature, it seems
reasonable to assume that matter has a wave nature.- DeBroglie proposed the following equation to describe
the relationship:
- The momentum, mv, is a particle property, where as is a wave property.
mvh
Chapter 7 22
The Uncertainty PrincipleThe Uncertainty PrincipleHeisenberg’s Uncertainty Principle - on the mass scale of
atomic particles, we cannot determine exactly the position, speed, and direction of motion simultaneously.
- For electrons, we cannot determine their momentum and position simultaneously.
Quantum Mechanical View of the AtomQuantum Mechanical View of the Atom
Chapter 7 23
- These theories (wave/particle duality and the uncertainty principle) mean that the Bohr model needs to be refined.
Quantum Mechanics
Quantum Mechanical View of the AtomQuantum Mechanical View of the Atom
Chapter 7 24
- The path of an electron can no longer be described exactly, now we use the wavefunction().
Wavefunction () – A mathematical expression to describe the shape and energy of an electron in an orbit.
- The probability of finding an electron at a point in space is determined by taking the square of the wavefunction:
Probability density =
Quantum MechanicsQuantum MechanicsSchrödinger’s ModelSchrödinger’s Model
Chapter 7 25
Quantum Mechanics
- The use of wavefunctions generates four quantum
numbers.
Principal Quantum Number (n)
Angular Momentum Quantum Number (l)
Magnetic Quantum Number (ml)
Spin Quantum Number (ms)
Quantum NumbersQuantum Numbers
Chapter 7 26
Quantum Mechanics
Principal Quantum Number (n) - This is the same as Bohr’s n- Allowed values: 1, 2, 3, 4, … (integers)- The energy of an orbital increases as n increases- A shell contains orbitals with the same value of n
Quantum NumbersQuantum Numbers
Chapter 7 27
Quantum Mechanics
Angular Momentum Quantum Number (l) - Allowed values: 0, 1, 2, 3, 4, . , (n – 1) (integers)- Each l represents an orbital type
l orbital
0 s
1 p
2 d
3 f
Quantum NumbersQuantum Numbers
Chapter 7 28
Quantum Mechanics
Angular Momentum Quantum Number (l) - Allowed values: 0, 1, 2, 3, 4, . , (n – 1) (integers)- Each l represents an orbital type- Within a given value of n, types of orbitals have slightly
different energy
s < p < d < f
Quantum NumbersQuantum Numbers
Chapter 7 29
Quantum MechanicsQuantum Mechanics
Magnetic Quantum Number (ml).
- This quantum number depends on l. - Allowed values: -l +l by integers.-Magnetic quantum number describes the orientation of the
orbital in space.
l Orbital ml
0 s 0
1 p -1, 0, +1
2 d -2, -1, 0, +1, +2
Quantum NumbersQuantum Numbers
Chapter 7 30
Quantum MechanicsQuantum Mechanics
Magnetic Quantum Number (ml).
- This quantum number depends on l. - Allowed values: -l +l by integers.- Magnetic quantum number describes the orientation of the
orbital in space.- A subshell is a group of orbitals with the same value of n
and l.
Quantum NumbersQuantum Numbers
Chapter 7 31
Quantum MechanicsQuantum Mechanics
Spin Quantum Number (ms)
- Allowed values: -½ +½.
- Electrons behave as if they are spinning about their own
axis.- This spin can be either clockwise or counter clockwise.
Quantum NumbersQuantum Numbers
Chapter 7 32
Quantum MechanicsQuantum MechanicsQuantum NumbersQuantum Numbers
Chapter 7 33
Representation of OrbitalsRepresentation of Orbitals
The The ss Orbitals Orbitals- All s-orbitals are spherical.- As n increases, the s-orbitals get larger.- As n increases, the number of nodes increase.- A node is a region in space where the probability of
finding an electron is zero.
Chapter 7 34
Representation of OrbitalsRepresentation of Orbitals
The The ss Orbitals Orbitals
Chapter 7 35
Representation of OrbitalsRepresentation of Orbitals
The The pp Orbitals Orbitals- There are three p-orbitals px, py, and pz. (The letters
correspond to allowed values of ml of -1, 0, and +1.)
- The orbitals are dumbbell shaped.
Chapter 7 36
Representation of OrbitalsRepresentation of Orbitals
The The pp Orbitals Orbitals
Chapter 7 37
Representation of OrbitalsRepresentation of Orbitals
The The dd and and ff Orbitals Orbitals- There are 5 d- and 7 f-orbitals. - Four of the d-orbitals have four lobes each.- One d-orbital has two lobes and a collar.
Chapter 7 38
Representation of OrbitalsRepresentation of Orbitals
The The dd and and ff Orbitals Orbitals
Chapter 7 39
32, 34, 42
Homework ProblemsHomework Problems
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