Chapter 7: Electronic Structure Electrons in an atom determine virtually all of the behavior of the...
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Chapter 7: Electronic Structure Electrons in an atom determine virtually all of the behavior of the atom. Quantum theory – the study of how energy and matter interact on an atomic level. To understand the electron, we must first understand light. Reason =
Chapter 7: Electronic Structure Electrons in an atom determine virtually all of the behavior of the atom. Quantum theory – the study of how energy and
Chapter 7: Electronic Structure Electrons in an atom determine
virtually all of the behavior of the atom. Quantum theory the study
of how energy and matter interact on an atomic level. To understand
the electron, we must first understand light. Reason =
Slide 2
Light Also known as electromagnetic radiation. Ex) Visible
light, Infrared, X-ray, Radio. All electromagnetic radiation have
several common characteristics. Light as a wave Light as a particle
Duality of Light
Slide 3
Electromagnetic Radiation
Slide 4
Light as a Wave Wavelength ( lambda) = Frequency ( nu) =
Slide 5
Light as a Wave Wavelength and Frequency are inversely
related.
Slide 6
Electromagnetic Spectrum Shows the full range of
electromagnetic radiation that exists.
Slide 7
Light as a Wave The product of the wavelength and the
frequency, though, is a constant. c = , where c is the speed of
light. Thus, if we know the frequency, we can find the wavelength
and vice versa. LEP #1(a).
Slide 8
Proof of Waves Waves exhibit certain properties when they
interact with each other. Youngs Double Slit experiment.
Slide 9
Proof of Waves
Slide 10
Slide 11
Light as a Particle The wave nature of light does not explain
all of the properties of light. Blackbody radiation when solids are
heated, they will glow. Color depends on the temperature.
Slide 12
Light as a Particle Max Planck proposed a theory that energy
from blackbody radiation could only come in discrete chunks or
quanta. E = h h = 6.626 x 10 -34 J s LEP #1(b).
Slide 13
Light as a Particle The photoelectric effect (Einstein) also is
proof that light must have a tiny mass and thus act as a particle
(photon). LEP #2, #3.
Slide 14
Line Spectra When a gas like H 2, Hg, or He is subjected to a
high voltage, it produces a line spectrum consisting of specific
wavelengths.
Slide 15
Line Spectra
Slide 16
High Voltage Excitation
Slide 17
Identifying Metals Na = yellow K = violet Li = red Ba = pale
green
Slide 18
Line Spectra The four lines for hydrogen were found to follow
the formula: Where the values of n are integers with the final
state being the smaller integer.
Slide 19
Bohr Theory How could such a simple equation work? Niels Bohr
some thirty years later came up with a theory. Classic physics
would predict that an electron in a circular path should
continuously lose energy until it spiraled into the nucleus.
Slide 20
Bohr Theory 1. An electron can only have precise energies
according to the formula: E = -R H / n 2 ; n = 1, 2, 3, etc. and R
H is the Rydberg constant. 2. An electron can travel between energy
states by absorbing or releasing a precise quantity of energy.
Slide 21
Bohr Theory
Slide 22
Can not explain the line spectra for other elements due to
electron-electron interactions. Thus, the formula for Hydrogen can
only be applied for that atom. LEP #4.
Slide 23
Matter as a Wave Louis de Broglie proposed that if light could
act as both a wave and a particle, then so could matter. Where h is
Plancks constant, m is the objects mass, and v is its velocity.
Size, though, matters. LEP #5.
Slide 24
Matter as a Wave De Broglie was later proven correct when
electrons were shown to have wave properties when they pass through
a crystalline substance. Electron microscope picture of carbon
nanotubes.
Slide 25
Uncertainty Principle German scientist Werner Heisenberg
proposed his Uncertainty Principle in 1927. History
Slide 26
Uncertainty Principle For a projectile like a bullet, classic
physics has formulas to describe the motion velocity and position
as it travels down range.
Slide 27
Uncertainty Principle Any attempt to observe a single electron
will fail.
Slide 28
Uncertainty Principle If you want to measure length, there is
always some uncertainty in the measurement. To improve the
certainty, you would make a better measuring device. Heisenberg,
though, stated that the precision has limitations. x m v h / 4
Slide 29
Uncertainty Principle Once again, size makes a big difference.
LEP #6
Slide 30
Uncertainty Principle Determinacy vs. Indeterminacy According
to classical physics, particles move in a path determined by the
particles velocity, position, and forces acting on it determinacy =
definite, predictable future Because we cannot know both the
position and velocity of an electron, we cannot predict the path it
will follow indeterminacy = indefinite future, can only predict
probability
Slide 31
Uncertainty Principle
Slide 32
Quantum Mechanics The quantum world is very different from the
ordinary world. Millions of possible outcomes and all are possible!
Quantum Caf I am convinced that He (God) does not play dice. Albert
Einstein
Slide 33
H = E Erwin Shrdinger proposed an equation that describes both
the wave and particle behavior of an electron. The mathematical
function, , describes the wave form of the electron. Ex) a sine
wave. Squaring this function produces a probability function for
our electron.
Slide 34
Atomic Orbitals A graph of 2 versus the radial distance from
the nucleus yields an electron orbital. An orbital is a 3D shape of
where an electron is most of the time. An orbital can hold a
maximum of two electrons.
Slide 35
Atomic Orbitals The Probability density function represents the
probability of finding the electron.
Slide 36
Atomic Orbitals A radial distribution plot represents the total
probability of finding an electron within a thin spherical shell at
a distance r from the nucleus The probability at a point decreases
with increasing distance from the nucleus, but the volume of the
spherical shell increases
Slide 37
Atomic Orbitals The net result for the Hydrogen electron is a
most probable distance of 52.9pm.
Slide 38
Atomic Orbitals For n=2 and beyond, the orbital will have n-1
nodes. A node is where a zero probability exists for finding the
electron.
Slide 39
Atomic Orbitals 2s orbital = 1 node 3s orbital = 2 nodes
Slide 40
Quantum Numbers An electron can be described by a set of four
unique numbers called quantum numbers. 1. Principle quantum number,
n = describes the energy level of the electron. As n increases so
does the energy and size of the orbital. n can have values of
integers from 1 to infinity.
Slide 41
Quantum Numbers 2. Azimuthal quantum number, l, defines the
shape of the orbital. The possible values of l depends on n and can
be all of the integers from 0 to n-1. However, the values of 0, 1,
2, and 3 have letter designations of s, p, d, and f,
respectively.
Slide 42
Quantum Numbers 3. Magnetic quantum number, m l describes the
orientation in space of the orbital. The possible values of this
quantum number are l 0 + l. When l is not zero, the magnetic q.n.
has more than one value. These multiple values produce degenerative
orbitals orbitals of equal energy.
Slide 43
Quantum Numbers 4. Spin quantum number, m s describes the
electron spin of the electron. This value is either +1/2 or
1/2.
Slide 44
Quantum Numbers
Slide 45
Pauli Exclusion Principle no electron in an atom can have the
same set of four quantum numbers. Ne = 10 electrons LEP #7.
Slide 46
Subshell Designations Value of l 0123 Type of orbital spdf
Slide 47
Orbitals s type orbitals are spherical in shape.
Slide 48
Orbitals p type orbitals have two lobes.
Slide 49
Orbitals d type orbitals generally have four lobes.