Transcript Kinds of Chemistry - Louisiana State University

Here’s what people said they learned.
LSU is the best school to go to EVER!
Ionic compounds: dating
Molecules: married
Water is a bent molecule, ain’t no HO.
It’s not terrible to not use a calculator.
Difference between molecular formula and empirical formula.
How to user periodic table better.
I need to read those CEF guides!
Welding is a physical transformation. (Mostly)
The vertical columns on the periodic tables FEATURE
elements with similar properties & behaviors.
All is not lost!
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Here’s what people said they wanted to know better.
Ionic compound formulas.
How to get an A on the
midterms.
Problems on the quiz.
Balancing equations…where
to begin.
How to classify what is solid, liquid or gas?
Why is H2O2 so much stronger as
an oxidant than H2O?
http://bezmuke.blogspot.com/2009/07/tigri-lei-gheparzi-leoparzi-pisici.html
Molecular formula vs.
empirical formula.
Calculator or nocalculator? I went no-calc
and made a 65. I never
made a 65 before.
When will we start
naming ions?
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Rarely, people forget to tear off their “action item for
self study”; here is one such example.
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I want to revisit our energy
relations
W = DE = mad (energy due to acceleration) =
mv2/2 (kinetic energy)
E = W = mgh (potential energy against gravity)
Q = m  C  DT
And E = mc2
There are more! How about E = hn
Does anyone recognize E= t  iV ?
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Where are we?
We have measured mass of proton: 1.66 x 10-24 g
We have measured mass of electron: 1836 times lighter than proton
We have measured charge of proton: +1.602 x 10-19 Coulombs
We have measured charge of electron: -1.602 x 10-19 Coulombs
We know protons are at the center of atom.
Neutrons were found—fixed the problem of “missing” atomic masses.
We expect neutrons to be at the center of atom, too (why?).
We imagine electrons are distributed around the atom somehow,
like satellites in orbit.
Because the electrons are so fast, we imagine them doing most of
work of chemistry: the currency of chemistry is electrons!
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I want to look at percents: here’s a CEF question.
The nucleus contains approximately what
percent of an atom’s mass ?
• 10.02%
• 60.49%
• 80.50%
• 99.97%
It’s going to depend on the atom, but ignore
that and answer the question: ATQ.
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We are still in:
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Read Chapters #4 later.
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Now we need to learn something about
waves.
Well, there are 2 kinds:
Longitudinal (sound)
Transverse (light)
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Let’s make some longitudinal
waves with a speaker.
High and low frequencies travel at the
same speed (almost).
This speed is called c = 1140 feet/second (in air).
How long does it take sound to travel 1 mile?
The sound gets louder and softer as
we travel about the room.
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Drums & cymbals are the original woofers and tweeters.
(Maybe boomers and clangers would be better).
l
Low frequency = long l
l
High frequency = short l
http://www.replayphotos.com/lsuphotos/traditions-pictures/band_T_OBN__0001024.cfm
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Speed = frequency  wavelength
c = nl
“nu”
“lambda”
Let’s get those units!
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Pinpointing the electron positions
required 2 breakthroughs, one conjecture,
and a lot of theoretical work.
The Einstein/Planck breakthrough (early 1900s).
1) Light can have wave AND particle properties!
2) The particles are called photons.
3) Each photon carries energy of:
E
hc
l
Low energy = long wavelength = red
h = Planck’s constant
c = speed of light = 3 x 108 m/s
High energy = short wavelength = blue
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Graceful swans
vs. hummingbirds
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Hey, what what are the
units of energy again?
Energy is the capacity to do work.
It has work units.
Work is force times distance.
Force is mass times acceleration.
So…. E  W = f  d = m  a  d
Units: kg  (m/s2)  m = kgm2/s2
This thing is called a Joule
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Joule, Calorie, Speed of light are all
things worth remembering.
1 Joule = 1 ntm = kg m2/s2
4.184 Joule = 1 Calories = 0.001 Food Calories
Planck’s constant: 6.63 x 10-34 Js
c = 3  108 m/s (= 186,000 miles per second)
How far IS 186,000 miles?
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Here’s a real-world sample problem.
A device we use to measure the size and shape of
molecules at CAMD (out on Jefferson Highway)
produces 3 x 107 photons per second at l = 1.5 Ǻ (0.15 nm).
What is this power output in Joules?
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Remember Emission Spectra—
what was the point anyway?
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Bohr atom (the hypothesis): electrons
have to stay on specific paths.
Dotted orbit: the “ground” state of hydrogen.
Solid orbit: one of the excited states of
hydrogen in a discharge tube.
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When an electron in the excited state
drops to lower state, light is emitted.
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When an electron comes out of a high orbit, into a lower
one, light is given off. From the wavelength, l, you can
calculate the difference in energies between the orbits.
D E = hc /l
We always deal with CHANGES in
energy; absolute energy is a mystery.
Needless to say, there are Bohr-ring videos!
Energy transitions: http://www.youtube.com/watch?v=8TJ2GlWSPxI&feature=results_video&playnext=1&list=PLC1E620BA406E7A75
Bohr-Ring Children: http://www.youtube.com/watch?v=PLpZfJ4rGts
Bohr-Ring Voice: http://www.youtube.com/watch?v=Ic8OnvRonb0
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What is this, physics?
Where is the chemistry?
View periodic tables!
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To explain* the periodic table, Bohr proposed
that the number of electrons each orbit can
support grows with the energy of that orbit,
described by an “energy quantum number”, n :
# of electrons = 2n 2
n = 1, 2, 3….
2n 2 = 2, 8, 18…
Energy and the number of electrons an orbit can
hold both increase with n.
*It can be argued that Bohr did not yet explain the table, but he
figured out its “code”.
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Periodic Table in its Standard Form
n=1 so 2n2 = 2  2 elements on top row
n=2 so 2n2 = 8  8 elements on 2nd row
n=3 so 2n2 = 18  ooops!
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Hey, it works….for small atoms.
st
1
row of periodic table: 2 atoms
2nd row: 8 atoms
3rd row: ooops!
That is a big “ooops” and, besides, Bohr
was not able to explain WHY the electrons
had to circle around on these discrete,
quantized orbits.
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The periodic table we usually see cuts out Actinides
and Lanthanides, “problem” elements with l=3 (f
orbitals). This wide-screen version is better.
http://www.sciencegeek.net/tables/LongTable2000.png
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The de Broglie Breakthrough (1924):
Electrons are waves (and particles).
Wave-particle duality
l = h/mv or... mvl= h
m = mass
v = velocity
l
(h = 6.63  10-34 Js)
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Oh great….now even chemists, the masters of electrons,
need to understand waves. Let’s do waves again.
pronounced “lambda”
pronounced “nu”
Oldest physics joke: what’s n?
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Waves diffract. They can “stand” if the
dimension of their “container” is right.
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Wave addition is weird: out-ofphase waves cancel.
+
=
Nothing
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In phase waves add.
+
=
Bigger wave.
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Waves bounce (with inversion).
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What if there’s another wall located 4 wavelengths away?
The waves “stand”. See later videos of standing waves.
Now is a good time to Wiki.
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What if there’s another wall located 4.25 wavelengths away?
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It’s much better with video!
String standing waves
http://www.youtube.com/watch?v=-gr7KmTOrx0
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There is no net dissipation of energy
in “standing waves”.
Hmmm…..atoms don’t seem to need to have
energy added, either, but where’s their wall?
Do we need a wall
for a standing wave?
After crossing between the walls twice, the essential
feature is that the wave has come back to where
it once was.
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Bohr’s circular orbits turn out to be wrong, but we can at least
see why orbits must be quantized: the waves would cancel
themselves out unless the ends meet smoothly. This is called a
“boundary condition”.
Crest
Node
Trough
Circumference = 2pli where i = 1, 2, 3
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There are no walls and no circular orbits in a real
atom, but electrons are nevertheless “confined” in a
zone, like sand on a vibrating plane:
Click for standing waves without walls
http://www.youtube.com/watch?v=GtiSCBXbHAg
Note the complexity of the wave goes up with
frequency…and one wave pattern gives way to
another by a “jump”.
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When you work the math…
the actual position of electrons can't really be specified
best we can do is say where they PROBABLY are
Erwin Schrödinger
they tend to locate in cloud-like zones (called orbitals, not orbits)
Orbital shape gets more complex with electron energy.
These shapes sort of "fall out of" the mathematics;
no human would have predicted them intuitively.
Additional quantum numbers
describe these shapes.
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Orbital shapes can be strange. Note the
extra quantum numbers!
http://www.albany.net/~cprimus/orb/
n=1, l=0, m=0
n=2, l=1, m=0
n=3, l=2, m=0
n=2, l=0, m=0
n=3, l=1, m=0
n=4, l=3, m=1
s-type
p-type
d-type (top)
f-type (bottom)
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Quantum Numbers are not that hard!
Our purpose:
Introduce the four quantum numbers
Explain how they relate to chemical periodicity
Explain how they relate to orbital shape & size
Give some more examples of physical periodicities
These are really the keys--keys as in open the door
to molecular understanding.
So pay attention!
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Four numbers describe more than 100
elements…that’s a beautiful simplification.
This will help you understand angular momentum.
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But why do we have to learn Quantum
Numbers? Isn’t that arcane?
Because I had to learn Russian.
And square dancing.
And accounting.
And Lissajous patterns.
And tennis.
http://www.youtube.com/watch?v=Ee_uujKuJMI
It is easier to fit in when you know stuff.
Try reading Zen & the Art of Motorcycle Maintenance! It’s about the quality
of life, which definitely includes knowledge.
Quantum makes it easier to understand later material.
You will be buying quantum computers.
Quantum Numbers are beautiful!
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A useless journey….but beautiful.
Mt. Chapin Trail
Rocky Mountain National Park
August 2011
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The Energy quantum number
determines how much diversity you
can have. Energy-rich electrons can
"buy" more “fancy” quantum states
than energy-poor ones.
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Shapes of atomic orbitals have to do with orbital angular
momentum: go back and watch gyroscope YouTube.
http://www.albany.net/~cprimus/orb/
n=1, l=0, m=0
n=2, l=1, m=0
n=3, l=2, m=0
n=2, l=0, m=0
n=3, l=1, m=0
n=4, l=3, m=1
s-type
p-type
d-type (top)
f-type (bottom)
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Row 1 contains elements with only
“low-energy” electrons.
if n = 1, then you can
have l = 0 only.
Then you can only
have ml = 0. ms can
be +1/2 or - 1/2.
Aha! There are only
two elements, H and
He, on the top line of
the periodic table.
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Row 2: now some electrons (the ones that
matter) have more energy.
if n = 2, you can have l = 0 or 1
For l = 0, you can have m l = 0
only.
ms can be +1/2 or - 1/2.
Check out Li and Be
For l = 1, you can have ml = 0 or
+1 or -1
For each of these three ml values,
you can have
ms = +1/2 or - 1/2 for a total of SIX
states
Check out the six elements: B, C,
N, O, F , Ne
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Crayola Periodic Table
1s
2s
3s
4s
2p
3p
3d
4p
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Electron configuration problems are easy!
There are all kinds of mnemonic devices for
this (see your textbook, CEF Study Guides,
Virtual Book) but the easy solution is:
Just follow the periodic table!
Example:
Calcium = 1s22s22p63s23p64s2
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Why does Calcium behave
rather like Barium?
Because both end in s2
What does it mean? The ending electron
is the one with highest-energy. This is the
one that does the most work. Its “work
habit” (orbital shape) is the same in calcium and barium.
If Donald Trump is in a hotel, he’s probably
the richest guest. Hotel assumes his personality.
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Stop here?
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