14 November 2011
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Transcript of 14 November 2011
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14 November 2011
Objective: You will be able to: describe evidence for the current
theory of the electronic structure of atoms.
Homework: p. 312 #3, 4, 5, 6, 7, 9, 16, 19, 25, 32
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Electronic Structure of Atoms
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Next Units:
Electron configuration Trends on the periodic table Ionic/covalent bonding Chemical reactivity
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In order to understand these things
we’ll study the electronic structure of atoms
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The Wave Nature of Light
electromagnetic radiation (a.k.a. light) is a form of energy with wave and particle characteristics. It moves through a vacuum at the speed of light
speed of light: 3.00x108 m/s
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To describe waves… wavelength (λ lamda): the distance
between two adjacent peaks of a wave frequency (v): the number of wavelengths
that pass a given point in a second
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Electromagnetic Spectrum
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electromagnetic spectrum includes all wavelengths of radiant energy
visible spectrum: the part of the electromagnetic spectrum that is visible to the human eye (wavelengths between 400 and 700 nm)
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Quantized Energy and Photons
quantum (a.k.a. photon) is a specific particle of light energy that can be emitted or absorbed as electromagnetic radiation.
Energy of a photon E=hv Energy is quantized – matter is
allowed to emit or absorb energy in discrete amounts, whole number multiples of hv.
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How are these things related to electromagnetic radiation?
v=c/λ E=hvλ = wavelength in nmv = frequency in 1/s or hertz 1 Hz = 1/s
E = energy of a single photon in Joules
c = speed of light = 3.00x108 m/s = 3.00x1017 nm/s 1 nm = 10-9 m
h = Planck’s constant = 6.63x10-34 J s
E=hc/λ
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Example 1
Calculate the energy (in joules) ofa. a photon with a wavelength of
5.00x104 nm (infrared region)b. a photon with a wavelength of
5.00x10-2 nm (x-ray region)
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Example 2
What is the frequency and the energy of a single photon?
What is the energy of a mole of photons of light having a wavelength of 555 nm?
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Problem
The energy of a photon is 5.87x10-20 J. What is its wavelength, in nanometers?
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Homework
p. 312 #3, 4, 5, 6, 7, 9, 16, 19, 25, 32
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15 November 2011 Take Out Homework Objective: You will be able to:
describe and explain experimental evidence for energy levels
Homework Quiz: The energy of a photon is 3.98x10-19 J. What color light do you observe?
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Agenda
I. Homework QuizII. Hand back testsIII. Line spectra and the Bohr model of
the atomHomework: p. 313 #23, 24, 25, 26,
30, 31, 35, 36
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Line Spectra and the Bohr Model
atomic emission spectrum (a.k.a. line spectrum): a pattern of discrete lines of different wavelengths that result when the light energy emitted from energized atoms is passed through a prism
Each element produces a characteristic or identifiable pattern
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Demo
Emission spectra of common cations Note: we don’t have a way to
separate all the wavelengths of light into discrete lines of color, so we’re just seeing all those lines of color blended together.
http://www.youtube.com/watch?v=2ZlhRChr_Bw&feature=related
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So, why do we see these discrete lines of color?
Bohr model of the atom: energies are quantized. Electrons move in circular, fixed energy orbits around the nucleus.
Usually, electrons are in the most stable “ground” state.
When energy (a photon) is added, they “jump” up to the “excited” state
They fall back down, and release that photon.
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Multimedia
http://www.youtube.com/watch?v=45KGS1Ro-sc
http://www.colorado.edu/physics/2000/quantumzone/lines2.html
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Homework
p. 313 #23, 24, 25, 26, 30, 31, 35, 36
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16 November 2011
Objective: You will be able to: explain how line spectra give
evidence for the existence of energy levels
explain how quantum mechanics describes electron configuration
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Agenda
I. Homework QuizII. Go over homeworkIII. How do atoms emit photons?IV. Quantum mechanics: how do we
describe where the electrons are?!V. Writing orbital notation and electron
configurationHomework: p. 313 #23-26, 30, 35, 48, 53,
60, 63,
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Energy levels
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Wave Behavior of Matter
Like light, electrons have characteristics of both waves and particles. Because a wave extends into space, its location is not precisely defined.
uncertainty principle: it is impossible to simultaneously determine the exact position and momentum of an electron. we can only determine the probability
of finding an electron in a certain region of space.
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Quantum Mechanics and Atomic Orbitals
quantum mechanical model: mathematical model that incorporates both the wave and particle characteristics of electrons in atoms.
quantum numbers: describe properties of electrons and orbitals each electron has a series of four
quantum numbers
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Table of Quantum Numbers
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Table of quantum numbers and orbital designations
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Pauli Exclusion Principle
Two electrons in an atom can’t have the same four quantum numbers Two electrons per orbital, with
opposite spins
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Representations of Orbitals
orbital: calculated probability of finding an electron of a given energy in a region of space
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p orbitals
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d orbitals
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orbital ≠ orbit
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17 November 2011
Objective: You will be able to: write the orbital and electron
configuration for any element describe several exceptions to the
orbital filling rules Homework Quiz: Describe, as
completely as you can in a paragraph or two, the evidence that convinced Neils Bohr of the existence of energy levels instead of a cloud of electrons.
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Agenda
I. Homework QuizII. Go over homeworkIII. Electron configuration notationIV. Problem SetUnit 4 Quiz Weds.
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Atoms with more than one electron
like hydrogen electron-electron repulsions cause
different sublevels to have different energies
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Order those orbitals fill
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Electron Configuration
distribution of electrons among various orbitals of an atom
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Rules for Writing E- Config.
at the ground state1. Fill the lowest energy level first. Electrons
in the same orbital must have opposite spins. Total number of electrons = atomic number
2. Only two electrons per orbital!3. Do not pair electrons in a orbitals of the
same energy until each orbital has one electron of the same spin (Hund’s rule)
4. Label each sublevel with the energy level number and letter of the sublevel
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Examples
1. phosphorus2. calcium3. iron
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Paired-ness of Electrons
Paramagnetic: an atom having one or more unpaired electrons Ex: Li, B, C…
Diamagnetic: all electrons in an atom are paired. Ex:
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Excited-State Configuration
has a higher energy than the ground-state electron configuration.
One or more electrons occupy higher energy levels than predicted by the rules
Ex: Iron in an excited state:
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Electron Configuration and the Periodic Table
Elements with similar electron configurations arranged in columns
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Examples
1. Write the electron configuration for palladium
2. Write the electron configuration for osmium
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Condensed Electron Config.
shows only the electrons occupying the outermost sublevels
preceded by the symbol for the noble gas in the row above the element
Example: calcium Example: iodine
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Unusual Electron Configs.
Cr and Mo: ground state valence electrons are arranged s1d5 rather than s2d4
a half filled d orbital is more stable than a more-than-half-filled d orbital
Cu, Ag and Au have s1d10 ground state configs because of the stability of a fill d orbital
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21 November 2011
Objective: You will be able to: describe the electronic structure of
an atom and make associated calculations.
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Agenda
I. Math with exponents (#6)II. Problem set work timeHomework: Problem set due
tomorrowQuiz Mon. on all electronic structure,
calculations, evidence for Bohr’s theory…
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28 November 2011
Objective: You will be able to: show what you know about the
electronic structure of atoms on a quiz
You need: periodic table calculator pen/pencil
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You have only one period Work smart: Go through the MC and answer
the ones you can easily answer. Then, go through and spend more time on
the difficult ones. Only write the noble gas notation if you need
electron configuration to answer a question. Only do the orbital notation of the parts you
really need to “see.” Don’t spend a long time on any one question
until you’ve tried every problem on the quiz. Pay attention to UNITS.