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Tuesday will be the
first weekly quiz,
celebration that is.
That will be at the beginning
of recitation.
You'll have 10 minutes.
It'll be a short one-pager.
You just write on the page.
All you bring is your periodic
table, which you should have
gotten in recitation
yesterday.
Periodic Table, table of
constants, calculator,
something to write with, but no
aid sheet on the weeklies.
Readings: Readings,
I urge you to read
before you come to class.
And so if you go to the
website, you can go to
Schedule, and in the schedule,
you'll see stuff like this
that tells you what the readings
are for the day.
As I mentioned last day,
the lectures are being
videographed and posted probably
within an hour on the
website and any of the images
that I show are also recorded,
burned as PDFs and uploaded.
So you don't have to be put in
high-speed stenographic mode
in order to attend class.
What's the other thing
I wanted to tell you?
If you're new to the class or
if you need to change your
recitation section because your
conditions have changed,
do not simply go to
the other class.
We're trying to regulate
enrollment,
particularly on Tuesdays.
If the TA shows up expecting 20
students and has 20 copies
of the quiz and 25 people
show up, that's not
a recipe for success.
So you must go to my
administrative assistant,
Hilary Sheldon in order
to change recitation.
And if you need any of the
handouts and so on, it's just
down the hall here in Building
8, Room 201.
I think that's all that
I had to say.
If you go here the videos
are all listed.
So last day we started talking
about taxonomy and that led us
to the beginnings of
atomic theory.
We visited with Democritus,
400 BC.
We had that detour with the
idiocy of Aristotle, and then
eventually got back to our
senses, and we saw John Dalton
with his table of the elements,
and then ultimately
onto Mendeleyev.
And I wanted to pick up
the thread there.
But before doing so, draw
attention the fact that John
Dalton did more than simply
develop a set of fonts for us.
So he proposed the model of the
atom and this goes back
little over 200 years ago,
and these are the
features of the model.
First of all, that matter is
composed of atoms that are
indivisible and indestructible.
So that goes all
the way back to
Democritus, nothing new there.
All atoms of an element
are identical.
Atoms of different elements
have different weights and
different chemical properties.
This is the emergence of modern
material science, the
connection between properties
and elements.
So the weight arguably is one
of the properties, but the
only way they could distinguish
elements at that
time was by their atomic mass.
Atoms of different elements
combine in simple whole-number
ratios to form compounds.
Well, that makes sense because
they're the elements.
They are the elemental
building blocks.
If I told you you could build a
structure made of blocks and
part-way through your
construction I say, why don't
you cut that block in half,
you'd say, well, then the
block isn't the building
block.
It's the half-block that's
the building block.
So axiomatically if these are
the elements they must combine
in simple whole-number ratios
to form compounds.
And lastly, atoms cannot be
created or destroyed.
Well, he wasn't foretelling
E equals mc squared.
What he was saying was that if
you take elements and you
combine them to form a compound,
if you subsequently
decompose the compound
you get the elements
back as they were.
So those are the features
of John Dalton's model.
And we fast forward to 1869.
And this is the knowledge that
was available at the time in
terms of the elements that
had been isolated and
characterized.
And it was with this
set of elements
that Mendeleyev operated.
On file cards, in his breast
pocket, he carried with him
everywhere.
And he wrote down the names of
the elements and their atomic
masses and their properties and
whatever else he could use
the way of characterizing
them.
And during the course of
writing a textbook--
he had just finished a chapter
on the alkaline metals and he
was sitting in the railway
station playing
solitaire, and boom!
The flash came to him that you
don't put arsenic underneath
aluminum even though it's next
in mass to zinc. You move it
over and you don't even
put it under silicon.
You put it under phosphorus.
And furthermore, what he said
was there's going to be an
element here discovered under
silicon and it will have these
properties.
And let's look a little bit more
deeply at the properties.
But before doing so I want to
say that by announcing this
prediction of what the element
should be that's missing is
that we start to see the
evolution of principles of
modern chemistry.
First of all, he recognized
the pattern.
So did Lothar Meyer
in Tuebingen.
So they both proposed a
periodic table of the
elements, but where Mendeleyev
pulled away from the pack and
distinguished himself was
that he developed a
quantitative model.
And I haven't shown you the
quantitative aspect yet.
That's coming next.
That explains the observations,
and that's good.
You might say, well,
that's just curve
fitting if you're a cynic.
But it makes predictions that
can be tested by experiment,
tested by experiment.
So let's take a look.
He said that under silicon, but
above tin, there would be
an element.
He called it eka-silicon.
Eka is a Sanskrit word,
which means one after.
So this is the element
one after silicon.
It was eventually isolated and
given the name germanium.
Mendeleyev said it would
have an atomic mass of
72 grams per mole.
In fact, it's 72.59.
He said it would have a density
of 5.5 grams per cubic
centimeter.
It's 5.36.
This is 1869.
He said that it would have a
high melting point, whatever
that means, and it melts
at 958 Celsius.
It's compounds.
he said it would form a dioxide
with a high melting
point and a density of 4.7.
It forms a dioxide and
its density is 4.70.
In fact, there's a story about a
French mineralogist who came
upon some of the stuff that
ultimately became germanium
dioxide, measured its density
and reported it to Mendeleyev
in a letter, saying, you know I
measured the stuff and it's
5.3 grams per cubic
centimeter.
Mendeleyev wrote him back
and he said, make
the measurement again.
You're wrong.
He wrote back three months
later and said,
I measured it again.
It's 4.7.
That was the genius
of Mendeleyev.
To go way out on a limb and
make those predictions.
And so I've made the case for
the table of the elements.
Why do we call it the
Periodic Table?
What's the periodic about?
Well, the periodic--
take a look here, if you go to
the website there's a tab
called Courseware and there's
a tab called Periodic Table.
And you can go to the Periodic
Table and ask the software to
plot property.
So for example this is boiling
point versus proton number or
atomic number.
And so you see the boiling point
varies as you move from
low atomic number to
high atomic number.
But it's not totally random.
It's not a Gaussian
distribution.
There are features.
It goes up and down, up,
down, up and down.
If you train your eye a little
bit you'll actually see some
regularity, a pattern there.
Maybe that's not so good.
Let's look at this one.
This is electrical
conductivity.
And again, up, down, up, down
and look at those red lines.
There, there, there, there.
Don't you see something?
That's a pattern.
And they're almost
equally spaced.
So that was where Mendeleyev
announced his Periodic Law,
where he said the properties are
related to the identity of
the atoms. And furthermore, he
announced, that the properties
are a periodic variation
in atomic mass.
So let's get that now
Mendeleyev's Periodic Law, and
the properties of the
elements vary
periodically with atomic mass.
That was Mendeleyev.
So now that we know that we can
go forward, and here's now
the full-blown Periodic Table
according to the framework
that Mendeleyev established.
Now if you look at this
carefully, you'll see down
here things get whited out
and there's these strange
notations, uu, m, and
all that stuff.
What's that all about?
This is where the super
heavies lie.
These are all synthetic
elements.
Transuranic, they're made by
high-energy reactions,
so-called high-energy physics
in what you might call
accelerators, atom smashers,
what have you.
And there's only three places
on the planet where you can
conduct such reactions.
One of them is in Darmstadt
in Germany.
One is in Dubna, just
outside of Moscow.
And if you want to stay home--
and eschew the frequent flyer
miles-- you can go to
Berkeley, California.
These are the three places where
we have the accelerators
capable of making
such compounds.
And so, take a look carefully
at what the nomenclature is.
The way you name them is by
using these Latin ordinals.
So un, bi, tri, quad
and so on.
So if you wanted to name element
115, it's ununpentium.
You want the ium ending.
And you can make these up.
You could make up element 205
if you want to or whatever.
My favorite is 111 because
that's unununium.
But there they are, so you
can have fun with those.
But with time, the elements are
being named and these have
been synthesized since
your version of
the table was printed.
And so number 110 is named
Darmstadtium in honor of the
team at Darmstadt that
first isolated it.
And number 111 was just named
two years ago and the name is
roentgenium after Wilhelm
Roentgen,
who discovered x-rays.
Now what is it about
discovery?
Well, here's an example of one
such reaction that would give
you an element.
So if we had access to one of
these devices we could take,
for example, lead and nickel and
accelerate them to very,
very high energies.
And then we could make
110, ununilium.
Or now we'll call it
Darmstadtium plus neutron.
And in doing so we've generated
the new element.
But we can't just say we've made
the element and publish.
We have to be able to
characterize it.
Remember the reason that we gave
Cavendish the credit for
discovering hydrogen wasn't that
he's the first to know
that hydrogen exists, but he
isolated it and gave it value.
So if you look at the rest of
the periodic table, you get
things like boiling point,
melting point, density,
electronegativity, first
ionization energy.
There's a lot of information
there.
If you go down here
there's nothing.
It's all blanks.
These things have very,
very short lifetimes.
Fractions of a second.
But you have to isolate them.
There's certain criteria
before you can publish.
And all this is regulated by
this governing body called the
International Union of Pure
and Applied Chemistry, So
UPAC, the organization that
finally rules on the
legitimacy of any of these.
And actually there have been
some retractions in recent
years, where people published
claiming--
I think there was a report out
of Berkeley claiming that
they'd synthesized 115 and then
subsequently that was
retracted because they couldn't
support the property
measurements
Last thing is, if you're
interested, want to do some
extra reading, there's a
fantastic book about
Mendeleyev.
He was the youngest of 14
children, came out of a very
poor family in Siberia and rose
to be a giant of his day.
He was a polymath.
He, among some of the other
things he did, he worked for
the Ministry of Weights and
Measures under the czar.
The czar was interested in
taxation of alcohol.
And if you mix equal volumes of
water and vodka you don't
get additivity.
So 100 mL of water plus 100 mL
of vodka doesn't give 200 mL.
It gives less.
And so Mendeleyev did a study to
determine what the optimum
ratio is so that people couldn't
misrepresent the
amount of alcohol
in the beverage.
And set the standard at 40%
alcohol by volume, which is
used the world over
to this day.
He also came to the United
States in 1876 to go to
Titusville, Pennsylvania,
where the first
oil well was drilled.
And did an exhaustive study
of what was the American
petroleum industry
at the time.
And then went back to Imperial
Russia and did the same survey
for the Czar in Imperial Russia,
including a report
that recommended how to develop
the natural resources
of the time.
He was really an amazing man.
He wrote text books and so on.
And nobody in science--
I would venture to say--
has not heard of
the periodic table.
Mendeleyev died in 1906.
The Nobel Prizes were first
offered in 1901.
So there were five years where
he was close to the top for
winning the Noble Prize but was
eked out by somebody else.
When you look back at
those other Nobel
Prizes, they were deserved.
But none more so than
that for Mendeleyev.
So ironically the man who gave
us seminal knowledge of all
chemistry was never awarded
the Nobel Prize.
And there's probably a lot
of politics in there.
And as I said last day, here's
the typical picture of him.
In this he sort of looks
like a street person,
disheveled and so on.
But this was the man that gave
us the periodic table.
That's him at age 35 when he
annunciated the Periodic Law.
So good for him.
Alright.
So now, let's take a look a
little deeper about the
properties of the elements.
How do we understand the
properties of the elements?
For the properties elements
we're going to have to look
inside the atom.
If you did your reading
you undoubtedly
came across this table.
Which at first pass,
deconstructs the atom into
three simple particles:
the electron, the
proton and the neutron.
Here are their symbols,
e, p and n.
And they're distinguished
by charge and mass.
So the electron has charge,
minus 1.6 times 10 to the
minus 19 Coulombs.
And a very low mass: 9.11
times 10 to the minus 31
kilograms. The electronic charge
is balanced by the
protonic charge.
The atom is net neutral.
So the proton has a charge of
plus 1.6 times 10 to the minus
19 Coulombs.
The neutron, as the name
implies, has 0 charge.
The proton and the neutron
have very nearly
equal masses, however.
Right.
And just a word about
the units.
The units here are given
in terms of the Systeme
Internationale.
So when we use the term, C,
capital C is for the Coulomb.
And that's the unit of charge.
And it has an uppercase letter
because it's named after a
scientist. In this case, the
French scientist, Coulomb,
whereas the gram is
not named after a
scientist and so it's lowercase.
And then we can amplify
by powers of three.
So if I want 1,000 of these,
I put a lowercase k here.
If I put an uppercase K, I end
up with the unit Kelvin, which
is the unit of temperature
named after Lord Kelvin.
And all of this is known as
SI units, which is the
International System.
And it's not because the
scientists don't know how to
develop an abbreviation.
This was originally developed
when French was the
international language
of science.
So this is known as the Systeme
Internationale and all
of these units were defined
at that time.
And the term SI sticks
that's the legacy.
All right, so now if we go
to the Periodic Table.
When we start looking at the
elements, we can look at any
entry on the Periodic Table,
and we have the chemical
symbol that I'm designating here
as uppercase X, and this
was originally John Dalton
with the I and the
circle around it.
And about 30 years later the
Swedish scientist Berzelius
suggested that we use neutral
units and so therefore we have
the Latin coming in for many of
the elements, such as iron,
Fe, ferrum, and gold
Au, aurum.
In the upper-left corner,
we have the quality I'm
representing here, A And
A is the mass number.
Some people call it
the atomic weight.
And it is the sum of the
masses of all the
constituents.
So it's the sum of the mass of
the protons, so it's the
proton number plus the
neutron number plus
the electron number.
But since the electron weighs
1/1800 of what these others
weigh, you normally don't
consider this.
It doesn't matter.
So just adding protons plus
neutrons gets you to what we
call the atomic weight.
And then down in the lower left
corner we have Z and Z is
the proton number.
And as the name implies, it's
equal to the number of protons
in the nucleus, which then
equals the number of electrons
outside the nucleus in
the neutral atom.
Now I'm specifying neutral
atom, because it's not
necessary for atoms to be
neutral and we'll take a look
at those in a moment.
A point about redundancy here.
We don't really need the proton
number and the chemical
symbol because the proton
number really defines.
The proton number is like the
Social Security number.
This is the identity
number of the atom.
If we change the the
proton number,
we change its identity.
So for example, I could
write sodium.
Sodium 23 and 11.
I don't need the 11.
11 means it's sodium or
sodium means it's 11.
So I could just write
this as 23 sodium.
So I know it's sodium, that
means it's got 11 protons and
23 minus 11 must be neutrons.
Or if I wanted to be a
smart aleck, I could
write this : 23 11.
That's sodium.
I don't need to put
anything here.
But there's no smart alecks
here, of course.
So for example, we could then
show this reaction as--
this is what?
208.
This is lead, 208.
And nickel, 62 gives us
Darmstadtium with a value of
269 and the neutron is 1.
You can see how these reactions
can be made to go.
Now atoms don't necessarily
have to be net neutral.
We can have something that
is net non-zero charge.
Net non-zero charge on the atom
gives it the term, ion.
Ion is an atom with net
non-zero charge.
And we have two cases where
the atom is net positive.
If the atom is net positive
that's the result of electron
deficiency.
The atom is electron
deficient.
And we term such an
atom the cation.
There's two types of ions.
The cation.
And then we have something
that is net negative.
If it's net negative, it means
it's electron-rich.
That is to say, there are more
electrons than protons and the
net negative ion is
called the anion.
And you can try to
figure out ways.
I sometimes think that cation
has a t, which looks a little
bit like a plus sign.
Anion has five letters, minus
has five letters.
And they both end in n, but
this has an n, which is
negative or something.
You'll figure something out.
Now we've talked about
varying charge at
constant proton number.
But the other thing we can
do is we can look at--
you can vary the
neutron number.
Since the neutron has no
charge you can vary the
neutron number and not harm the
identity and still have a
neutral atom.
So vary neutron number at
constant proton number.
And let's see what that is.
That gives you something
that looks like this.
So for example, if you if you
look at carbon, the atomic
mass that's shown
here is 12.011.
And you'd say, well, gee, if
it's got 6 neutrons and 6
protons, why isn't
that 12 exactly?
Well, this is the answer here.
You can vary the neutron
number at
constant proton number.
So let's take a look at
how that plays out.
The way that plays out
is as following.
Let's see I'm going to make
a little table here.
So we'll start with carbon 12.
Carbon 12, so that means--
now I know what I'm
going to do.
I'm going to bring this down and
make some headings for me.
This will be my proton
number and this will
be my neutron number.
And finally I'm going
to talk about
abundance, natural abundance.
So carbon 12, since it's carbon,
axiomatically it must
have 6 protons.
And 12 minus 6 is 6, so
it's got 6 neutrons.
And this is the dominant
form of carbon.
If you took a chemical analysis
of the carbon you'd
find that over 98%, 98.892% of
the carbon atoms that you
examined would be of this
form, carbon 12.
Now there's also carbon 13.
Has to be 6, otherwise
it's not carbon.
That means it's got
7 neutrons.
And it's a minority species.
1.108%.
And then there's a third
form of carbon and
that's carbon 14.
Again, has to be 6 and
it's got 8 neutrons.
And it's found in vanishingly
small quantities, one part in
10 to the 12.
Or we could call it ppt,
parts per trillion.
So this is same atomic number,
same proton number, same Z but
different mass numbers.
Different A's.
So all of these variants of
carbon are found on the same
place, the same spot on
the Periodic Table.
The Greek word for same is iso,
and the word for place is
topo, so these are
called isotopes.
The isotopes of carbon are
species that have identical
proton number but different
neutron number.
How about the units?
What are the units here?
Well, we have to give
some kind of unit.
I've been sort of freely going
around and counting protons as
one and so on.
And here's the standard.
The standard for mass is
defined, and the definition
goes like this.
If you take carbon 12, which we
just introduced to you, and
we say that we're going to
specify a mass of 12.000 grams
exactly for a specified
quantity, in other words, a
specified number of these atoms.
We have to say we'll
take a certain number of these
carbon atoms and specify the
mass of that number
is 12 exactly.
And specified number of
atoms being the mole.
The mole.
And it turns out that the mole
has a value of 6.02 times 10
to the 23rd.
How do they get that number?
A little bit more in the
way of definitions.
It was a concept put forth
by a professor.
So we're going to take some time
on it because we respect
professors, in this class at
least. And so this was a
concept put forth by Professor
Amadeo Avogadro.
Professor Avogadro, who was a
professor of physics at the
University of Turin, Torino.
And he was a contemporary of
John Dalton's and they were
both studying gases.
And it was Avogadro who taught
us that, when you keep the
pressure constant equal volumes
of different gases
contain equal numbers
of molecules.
It doesn't matter if you have
argon, which is by itself
atomic, or we have oxygen, which
is diatomic, or you have
methane, which is CH4, five
atoms making a compound.
Equal pressure, equal
volume, equal
numbers of those species.
So that was Avogadro's Law.
So let's put that down.
At constant pressure equal
volumes of different gases,
contain identical numbers of
atoms. Equal volumes of
different gases contain equal
numbers of molecules.
And here I'm using the term
molecule as a counting unit.
So it could be, strictly
speaking, an atom or it could
be diatomic and so on.
That's what it was.
And out of honor for Avogadro,
we name the number of atoms in
the mole the Avogadro number.
Which I've written 6.02
times 10 to the 23rd.
Now how do we determine
Avogadro's number?
That's an interesting story.
So first of all, we need two
pieces of information.
Because we're going to do this
by the noblest form of
chemistry, electrochemistry.
So the first thing we're going
to do is we're going to look
at the work Michael Faraday
in England.
And what Michael Faraday
did is he studied the
electrodeposition of metal.
And specifically he passed
current through a cell and he
electrodeposited silver.
So he starts with silver plus,
that's silver a cation, and by
the action of electric current
attaches an electron to silver
and renders it neutral.
Silver, which now plates out
onto an electrode and they
measured the mass.
They measured the mass of
silver-plated and they compare
it to the amount of charge
that was passed.
They measured the charge.
And you can get charge, because
you know current.
So charge is simply equal to
the integral of the current
times the time.
You know the current,
that's easy.
And what Faraday found was that
to make what we now know
to be 108 grams of silver, 108
grams of silver, which we're
going to subsequently recognize
as the mole, which
is identical to the amount, the
number of particles in 108
grams of silver, is equal to the
number of particles in 12
grams of carbon.
Sort of an Avogadro-type
harkening.
He found that that is--
the equivalent requires
96,485 Coulombs.
So you can say 1 mole of
electrons gives me 1 mole of
silver, so that's the charge on
1 mole of electrons, where
Coulomb is the elementary
charge, because we know 1
electron per 1 silver
atom deposited.
So now if I know that's a mole
of electrons, I need to find a
charge on one electron, divide
through and I get
the Avogadro number.
And to finish the story we have
to wait about 50 years
and come to the United States,
where it's Robert Millikan,
Robert Millikan at the
University of Chicago doing
the oil drop experiment through
which we learn the
elementary charge.
And here's the cartoon of
the oil drop experiment.
I took this from a
different text.
It's not shown in your text.
So I actually did this
experiment as a sophomore at
the University of Toronto.
They had us repeat some of the
great experiments of physics,
the ones that were accessible,
obviously.
I couldn't do high-energy
physics in an afternoon.
That would have taken me
a little bit longer.
But we did this one.
And so it consists of an
atomizer, sort of a perfume
atomizer, in which
there's oil.
And by the action of atomization
we form a shower
here, a very, very fine
dispersion of
tiny droplets of oil.
And then-- this cartoon is hard
to make sense of so I
fixed this--
we shine high-energy
radiation on this.
And by the action of high energy
radiation we take these
neutral droplets and we
turn them into ions.
We eject electrons.
And so now these are charged.
And then we charge the plates.
So if we have neutral species
and they simply come out of
the atomizer, they'll settle
under gravity.
But now if they're charged and I
put a charge on the plates--
let's say as here the upper
plate is positive--
if any of these particles is
charged positive, the action
of the electric field will
accelerate the descent,
because the bottom plate is
negative attracting and a
positive plate at the
top is repelling.
And vice versa.
If I have a particle that's
negative, the upper positive
plate will actually cause it
to slow down, and in the
extreme, it may actually
start to rise.
And so what Millikan did is a
set of experiments in which he
studied all the different
particle sizes.
See this telescope?
Right over here is Millikan.
And Millikan's sitting
there and he's
squirting and he's watching.
He's measuring the settling
velocity.
And he changes the magnitude
of the electric field.
He changes the intensity
of radiation.
He changes the nozzle.
He changes everything he can.
And what does he find?
He finds that the distribution
of velocities is not
continuous.
It's not continuous.
You think, well, gee if you just
keep dialing you should
get every variation
of velocity.
Well, he doesn't.
He finds that he gets variation
down to a single
value, below which
he can't go.
He determines that electric
charge is quantized.
That is to say there's
a base unit.
It's an element.
I just talked to you about the
elemental building block.
That's an element
in mass space.
Now I'm going to go
conceptually into charge space.
There is an elemental building
block of electric charge.
Electric charge is quantized.
And he found that the elementary
charge, which we
gave the symbol, e.
e is not the symbol
for electron.
e is the symbol for
elementary charge.
It has a value, if you convert
it to modern SI units, of 1.6
times 10 to the minus
19 Coulombs.
So now I can take these two
pieces of information, Faraday
which is up here.
This is known as the
Faraday Constant.
Script f, Faraday constant.
So if I divide the Faraday
constant, which is the charge
on a mole of electrons, by the
elementary charge, which is
the charge on one electron,
presumably I should end up
with the Avogadro number.
It should be the ratio
of the Faraday to
the elementary charge.
And it gives us--
for the third time
this morning--
6.02 times 10 to the 23rd.
If you like per mole, yes
or no, doesn't matter.
So now, what's the
atomic mass unit?
Now we can say the atomic mass
unit is, 1 atomic mass unit
then must equal what?
It's going to equal 1/12 of
the mass of carbon 12.
1/12 of the mass of carbon 12
divided by the Avogadro
number, which gives us 1.661
times 10 to the minus 27
kilograms.
Now be careful because
the system is just
a little bit rickety.
You know we went SI, but look,
this is still defined as 12
grams. And so sometimes if you
look depending on where this
is, 10 to minus 27 kilograms or
10 to the minus 24 grams.
Just be careful.
If you ignore this you'll be off
only by factor of 1,000.
That's a joke.
But it's lost here.
People are too serious.
We'll lighten you up.
All right, so enough
of the history.
Let's now do something
dynamic.
So far we've been studying
static elements.
But chemistry is really the
action of elements in motion.
So how do we describe
a chemical reaction?
Let's look at that.
What are the rules to describe
a chemical reaction?
Write an equation.
Write the equation of the
chemical reaction subject to
these rules.
There are two simple rules.
One is conservation of mass.
We've been told the repeatedly
since Democritus,
conservation of mass.
And the second thing, we use
Dalton's Law of Molar
Proportions.
That is to say, the building
blocks in integer ratios.
And so I thought I'd
do this in context.
So I've got a specific
example here.
So this is something that
I'm interested in.
Some of my research is in
metallurgical extraction by
benign processes.
What you're looking at is
a billet of titanium.
To give you a sense, you can see
the stairwell back here.
So this is about 4 feet, a
little over a meter here.
So you can see this is one
honking big piece of titanium.
This came out of the primary
reactor, the Kroll reactor and
this is subsequently swaged and
hot worked and so on to
form these billets.
So this is the first step of
turning dirt into metal.
That's called titanium sponge.
And titanium sponge occurs
inside a Kroll reactor.
It occurs inside a Kroll
reactor, which was invented by
a man of the surname Kroll in
Luxembourg in the 1930s.
And then with the advent of
World War II, he decided to be
smart, to get out.
And he ended up in Oregon where
he became a professor.
So he's known as Professor
Kroll, although the truth be
told he really made
his discovery
before he became a professor.
But he's still a professor
and so we'll honor him.
And so the Kroll process for
making titanium centers around
this reaction.
Here's the reaction written
according to the rules above.
We take titanium dioxide, which
is found in the Earth
and by some prior chemistry
convert it to titanium
tetrachloride, and in a reactor
that I'm going to show
you in a moment, we
react titanium
tetrachloride with magnesium.
And magnesium has a higher
affinity for chlorine than
does titanium and steals the
chlorine from titanium to form
magnesium chloride, leaving
behind titanium metal.
Now we have to have conservation
of mass.
So you can see, I've got 4
chlorines on the left but only
2 chlorines on the right.
So I'm going to put a
2 here and double
the magnesium chloride.
But now I've got 2 magnesiums
on the right and
only 1 on the left.
So I'll put a 2 in front of the
magnesium and now we have
a balanced equation.
And here's what the reactor
looks like.
You can imagine a giant vessel
with a pressure seal on the
top and a couple of valves,
big enough to make this.
So this is about 15
feet by 30 feet.
And so we introduce titanium
tetrachloride, which is a gas,
and magnesium as a solid and
heat to 900 degrees C.
And at 900 degrees C, if you
look on your Periodic Table
you'll know that magnesium
melts at 650 degrees C.
So we have a liquid sitting
here, titanium tetrachloride
here, and this thing
is sealed.
It's called a bomb reactor.
Nothing can get in, nothing
can get out.
The pressure builds up here.
And right at this interface
the titanium tetrachloride
reacts with the magnesium
according to this reaction.
Now this is very interesting.
It's beautiful reaction
because the titanium
tetrachloride is a gas;
magnesium is a liquid.
Magnesium chloride is a liquid,
but it is of different
density, and it is insoluble
in magnesium, and titanium
melts at 1670 and
it's a solid.
So what happens over
time is this.
The magnesium chloride that
forms pools underneath the
magnesium liquid, gets out
of the way so that we can
continue to keep this interface
clean and have the
reaction proceed.
You don't want to reaction where
reactant A reacts with
reactant B, makes a product that
covers the interface and
now the product is in the
way of future reaction.
So this is very elegant because
I don't need any fans,
I don't need any nose
propellers, nothing.
By density the magnesium
chloride settles and the
titanium settles.
And it's sitting here
at the bottom.
And you can imagine if we do
this long enough, this
titanium at the bottom will
continue to build until it
looks like this.
As long as you keep feeding
TiCl and Mg.
See I'm talking metallurgy
now.
TiCl and Mg, that's
what you make.
So that's how we make titanium,
first step.
And so suppose you get hired and
it's your first day on the
job and you're working at
Cambridge Titanium and the
boss says let's put in 200
kilograms of TiCl and we'll
put in 25 kilograms of Mg.
And the question is,
what is the yield?
What is the yield?
How much titanium are
we going to make?
Well, you say, just
multiply it out.
But first you have to see if
things are in balance.
We have to study the
stoichiometry of the reaction.
Stoichiometry, what
does this mean?
It's from the Greek, stoicheia,
which has to do
with measurement proportions.
So if these are not put in to
the reactor in proportion to
what they are in the equation
we're not going to get the
yield here.
So first thing I gotta do, this
is in moles, this is in
kilograms. So I have to convert
the kilograms to moles
and then maybe I can make
some sense of this.
So if I divide by the atomic
mass of titanium, four times
the atomic mass of chlorine and
convert; I will discover
that I have 1,054
moles of TiCl.
And I've got about 1,029
moles of magnesium.
Well, this equation says I need
2 times the amount of
titanium tetrachloride.
Well, it's obvious to the naked
eye, 1,029 isn't two
times 1,054.
So I've got a problem here.
I'm not going to get as much
titanium as I put in.
Titanium chloride.
This yield is going
to be restricted.
It's going to be restricted by--
this is sort of a chain
is as strong as its
weakest link--
the yield is restricted by the
amount of limiting reagent.
And in this case, magnesium is--
this is less than 2 times
the mole number of titanium
chloride.
So this means this is the
limiting reagent.
Alright so now if we use that
principle then I'm only going
to get as much titanium as I had
magnesium and you can see
from the stoichiometry here,
if I've got 1,029 moles of
magnesium I'm going
to have half of
that number of titanium.
So therefore the amount of
titanium is equal to 515 moles
of titanium.
And you notice I'm not obsessed
about a significant
figures and so on.
It's a metallurgical plant.
Half of 1,029 is 515.
Is it 514.5?
If you wish.
I don't care.
So 515 moles and then I convert
that, which gives me
24.7 kilograms of titanium
when I use
that amount of magnesium.
And if you go to the text,
Section 2.7, you'll see the
nuts and bolts of how to
run these reactions.
For those of you who had a lot
of chemistry in high school, I
know this is review, but I want
to bring everybody up to
the same page.
So we're starting with this.
All right.
I think that's a pretty
good place to
stop with the delivery.
But I don't want you moving.
You don't move yet.
Because the last 5 minutes
I'm going to
still continue to talk.
But on a slightly
different topic.
And so I don't want to
hear the binders
snapping and so on.
We're here; you paid
your money.
Five more minutes.
Five more minutes and then
you're out there.
Out there, then begins
le weekend.
But not until then.
So a couple of things.
First is, the music today.
I try to link the music
thematically.
So the music playing today was
Polovstian Dance number 17
from Prince Igor, by Borodin,
Aleksandr Borodin.
Why were we listening
to this music?
Well, because I insisted
that we listen to it.
Well, what about Borodin?
Borodin lived in Saint
Petersburg.
He was a friend of Mendeleyev.
OK, that's cute but more
importantly Borodin wrote his
music in his leisure time.
He had a day job.
His day job was professor
of chemistry.
And he worked at the Medical
Surgical Academy in Saint
Petersburg.
He was an exceptional
human being.
In those days, women were
forbidden to attend
institutions of higher
education.
He set up an entire curriculum
for women in a night school at
the Medical Surgical Academy.
He cavorted with artists and
therefore obviously his
politics were radical.
And they were trying to reform
the political scene in Czarist
Russia at the time.
And he was also quite
a bon vivant.
And he died on his feet
dancing at a ball.
So that's the way to go.
Having a great time.
That was Borodin.
One other thing before you go.
You were very very dour, so I
thought I'd try to put you in
a good mood to the extent this
is possible with this group.
And I wanted to share
with you some news.
There's been a new element
discovered.
You know these atoms smashers,
they're always working.
And so the discovery of the
heaviest element known to
science has been reported.
The element, tentatively
named administratium.
I don't know if UPEC is going
to go for this, but you can
suggest names.
So they're going to name
is administratium, the
discoverers.
It has no protons
or electrons.
So that means its atomic
number is 0.
It does have one neutron, 125
assistants to the neutron.
75 vice-neutrons and a
111 assistants to the
vice-neutrons.
This gives it a mass
number of 312.
The 312 particles are held
together in the nucleus by a
force that involves the
continuous exchange of
meson-like particles
called memo-ons.
There's no electronic mail,
because there's no electrons.
There may be neutronic mail
but we don't know yet.
Now you've already learned
something today.
You know something.
Since it has no electrons,
what do we know about its
chemical reactivity?
It's inert.
It has no electrons.
It can't exchange.
So this is chemically inert.
So you say, how did
they detect it?
Because it seems to impede
every reaction in
which it is a present.
According to the discoverers
a few nanograms rendered a
reaction that normally takes a
fraction of a second, it took
now four business days
to conduct that same.
There are a few other
properties.
We know so far that
it's radioactive.
And we're going to study
radioactivity later, so
there's a little bit
of foreshadowing.
It has a half-life of about
three years, at which time it
stops decaying and instead it
undergoes a reorganization, in
which the vice-neutrons,
assistants to the neutrons and
assistants to the
vice-neutrons, exchange places.
Some studies indicate that the
mass actually increases after
each reorganization.
So you can imagine now we'll
have something like this.
See how this increased?
So if they occupy the same
place, they have the same
proton number, but a different
neutron number, in the case of
administratium, they're
called isodopes.
So with that I will say,
have a good weekend.
