Chemical History

A Quick History of
With thanks to Isaac Asimov
As easy as LMN
 No one knows where the Latin word “elementum”
comes from. We get our word ELEMENT from it.
 Some think maybe the Romans had an expression
that something was as simple as “L-M-N,” just as
we say something is as easy as “A-B-C.”
 We use the word element to refer to a substance
which cannot be broken down into a simpler
The Ancient Greeks
 Aristotle suggested that everything was composed of 4
 Water, Air, Earth and Fire
 He later added a 5th element which he called “aether”
which the stars and the heavens were made from.
 Aristotle also said that “cold” was a substance he called
primum frigidum, and that “cold” came from water.
 People actually believed this up until the middle ages
(1500s at least).
 Click on the next slide to see three of these “ancient
Earth Wind and Fire
Yes, I’m “old school.” But I love these guys. And, I even saw
them in concert once, back in the 80’s. OK, back to chemistry
history…on the NEXT slide…If you don’t have these guys on your
iPod, get some. Tonight. Seriously.
Democritus—400 BC
Democritus was the first to suggest
that matter was composed of atoms,
which he called “atamos” meaning
Unfortunately, he came from a small
“hick town” and people didn’t believe
him. Aristotle, for example, ridiculed
him. Because Aristotle was more
respected, Democritus’ ideas faded
into history for over 2,000 years.
The Alchemists: 1400-1600?
Roger Bacon was an English alchemist
who may have been the first European
to invent gunpowder. Alchemists
actually discovered some chemistry,
but mostly they were trying to figure
out a way to turn lead into gold.
They failed. However, with nuclear
reactions, which weren’t discovered
until the 20th century, turning lead into
gold is now possible, but it costs more
to make the gold (that way) than the
gold is actually worth.
An Alchemist at work…
Paracelsus was a famous alchemist who may
be depicted in this famous painting.
He discovered many of the properties of salt
in the 1500s. Salt had been known for
thousands of years, and in ancient times was
so valuable, it was actually used as money.
He was probably the first person to realize
that elements could come together to form
compounds, with different properties from
from the elements they are made from.
Paracelsus also is credited with discovering
Robert Boyle…the Last of the
A 17th century British nobleman, he met
Galileo and was an alchemist, and maybe
the first real scientist. Boyle invented a
vacuum pump, did many experiments on
gases, and is credited with “Boyle’s Law.”
P1 x V1 = P2 x V2
This law states that pressure and volume
are “inversely proportional” to each other.
More on Boyle
 Boyle started calling himself a “chymist” because the term
alchemist had gotten a bad reputation. The spelling was
eventually changed to chemist.
 He questioned the old Greek notions of the elements. He didn’t
believe water was an element, and he experimented on water to try
and prove that. Even though he didn’t quite prove that, he
believed water to be a compound, and the move away from
Aristotle’s theory of the elements had begun.
 He also experimented with cold temperatures, and whether water
froze at different rates based on the initial starting temperature.
He also scientifically explained some of the properties of ice.
 By the early 1600s, a few substances were known, but they weren’t
known to be elements yet. Gold and silver and copper and lead
had been used since the ancient times, but no one knew they were
 The alchemists actually did discover 4 elements in the middle ages
(As, Sb, Bi and Zn).
 By 1700, about 14 elements were known. By the end of the 1700’s,
around 1783, another 11 were known.
 Chemistry was evolving during this time, but few chemists paid
attention to the quantitative aspects of chemistry. They observed,
but they didn’t measure.
Phlogiston and Priestly
Phlogiston was a theory that explained
how things burned. Things that
burned would release phlogiston to
the air. When a substance had used up
all of its phlogiston, it would stop
Although it was disproven before he
died, he always believed he was right.
He also was the inventor of something
much more interesting: carbonated
Antione Lavoisier
Father of Modern Chemistry
Proved that air was composed of 1/5 oxygen
and 4/5 nitrogen
Demonstrated experimentally the principle later
renamed “The Law of Conservation of Mass.”
Proved that hydrogen and oxygen combine to
form water, proving at last that water was a
Beheaded on 5/2/1794 by guillotine during the
French Revolution at age of 50.
More on Lavoisier
 By insisting on careful measurement and thoughtful
experimentation, Lavoisier turned chemistry from a series of
interesting observations into a real science.
 He explained the results that others had gotten. They knew
what they had done. Lavoisier helped to explain why these
things had happened.
 He studied combustion reactions and discovered the
importance of oxygen in both combustion and respiration
(disproving phlogiston in the process).
More on Lavoisier
 He also invented the system of naming
chemicals that we use today.
 Prior to Lavoisier, people who discovered
things named them whatever they wished.
 He also published the first modern chemistry
text (Traité élémentaire de chimie) thus
spreading his knowledge literally around the
John Dalton
A Quaker schoolmaster (became a teacher at the
age of 12) who studied all sciences, but made his
greatest contributions in chemistry.
Developed Atomic Theory and Law of Multiple
Atomic Theory helped to explain many of the
observations that scientists were making.
Law of Multiple Proportions helped to explain
that 2 elements could combine to form more than
1 compound; for example CO and CO2.
Dalton’s Atomic Theory
 1. All elements are composed of tiny indivisible particles
called atoms.
 2. Atoms of the same element are identical. The atoms
of any one element are different from those of other
 3. Atoms of different elements can chemically combine
with one another in small whole-number ratios to form
 4. Chemical reactions occur when atoms are separated,
joined or rearranged. Atoms of one element cannot be
changed into atoms of another element by chemical rxns.
 Well, Dalton did this work in the early 1800’s.
 We know now that atoms are composed of protons, neutrons
and electrons. Dalton didn’t know about them—they hadn’t
been discovered yet!
 HOWEVER, the atom is “the smallest part of an element that
retains the properties of that element.”
 So an atom of gold is still gold and is different from an atom
of carbon.
 Dalton’s model of the atom is called the “solid sphere” model.
Dmitri Mendeleev
 Mendeleev organized the Periodic Table
by atomic mass.
 He left “holes” in his table for
undiscovered elements and challenged the
scientific world to “find them!”
 In the early 20th century, Englishman
Henry Moseley reorganized the Periodic
Table by putting it in order of atomic
 Element 101 Md (Mendeleevium) is
named after him. Moseley has not been so
honored yet.
JJ Thompson Discovered the
Electron in 1897.
Electrons are negatively
charged and have
almost no mass at all,
compared to a proton.
Thompson revised
Dalton’s model of the
atom with one of his
own, called the “Plum
Pudding Model.”
Plum Pudding Model
Plum Pudding is a British dessert in which
plums are scattered more or less randomly
throughout a cake (the pudding).
Thompson knew atoms contained
electrons, and knew they were negative.
He also knew that the atoms overall were
So, he proposed that the negative electrons
were randomly distributed throughout. The
rest of the atom was positively charged.
Thompson proposed the electrons were
moving in a circular fashion within the
positively charged “rest of the atom.”
Robert Millikan and the
Oil Drop Experiment
This is what he used to do it…
Robert Millikan
measured the exact
charge of the electron
in “The Oil Drop
Atoms can GAIN or
LOSE electrons to
form ions. Ions are
atoms with a charge!
 Electrons are negatively charged. Each electron has a charge of -1.
(Don’t forget the negative sign…it’s VERY important!)
Ernest Rutherford’s Nuclear
Model…it’s now 1910 or so…
The Plum Pudding Model wouldn’t last long,
because one of JJ’s former students did some
experiments that forced the model to be
revised again. Like his mentor, JJ Thompson,
Rutherford won the Nobel Prize for his work
His “work” was the famous “gold foil”
experiments, where he was researching alpha
particles (see Chapter 28 stuff again).
As sometimes happened, Rutherford didn’t
set out to discover what he actually did.
Rutherford is also credited with discovering
the proton around 1919.
The Gold Foil Experiment
Check out the link!
Reference for below…
Rutherford created a device
to “shoot” α particles at a thin
piece of gold foil, literally only
a few atoms thick.
He expected them to go
through with little or no
But that’s NOT what
happened. Some bounced
straight back as if they had
hit a brick wall!
Shocked, SHOCKED!
 Rutherford was completely surprised
by this result. He had accidentally
discovered the nucleus.
 Rutherford figured out that most of the
mass of the atom was contained in a
small, dense center which was
positively charged.
 The electrons still rotated around the
nucleus, but most of the atom was
composed of “empty space.”
Neils Bohr: The Planetary
Model & Energy Levels
Rutherford’s nuclear model only really lasted
for about 3 years, before Neils Bohr revised it
Soccer goalie on Denmark’s
1908 Olympic team AND a
Nobel Prize winner in 1922!!
Talk about student/athlete!”
His son also won a Nobel
Prize in 1975!
Bohr asked a question: if the electrons are
rotating around the nucleus, why don’t they
“run out of energy.” As they did, they would
come closer and closer, attracted by the
opposite charge of the nucleus, and eventually
collapse onto the nucleus, destroying the atom
in the process.
This doesn’t happen, and Bohr answered why.
Bohr’s Planetary Model
An old
But the electrons don’t just orbit anywhere.
They can only move in orbits that Bohr called
“energy levels.” Each energy level has a certain
amount of energy.
Electrons can move to a higher energy level by
gaining energy. Or they can drop to a lower energy
level by losing (or emitting) energy.
But they can’t “run out” of energy, because in order
to stay in an energy level, they must have that
certain amount of energy.
Energy Levels
 An energy level is a “region
around the nucleus where
an electron is likely to be
 The first energy level (n = 1)
has the lowest energy. It is
called “the ground state.”
 Things in nature prefer to
be in the lowest possible
energy state.
Spectral Lines for H
 Electrons can ABSORB
energy and move to a
higher energy level.
 This is called “an excited
state.” If an electron moves
from n=1 (ground state) to
n=3, it is in an excited state.
 When an electron loses
energy, it drops to a lower
energy level. When an
electron loses energy, we
The lines are characteristic for hydrogen. say it EMITS energy. If that
They are like a fingerprint to identify H.
energy is in the visible part
The Ballmer series is the only ones you
of the spectrum, we can see
can see, but the others can be detected.
those transitions.
More Bohr
 In Bohr’s model, the
energy levels get closer
together as you get
further away from the
 If the electron gets far
enough away from the
nucleus, it can escape (n
= ∞).
The electrons can jump from one level to
another. They can jump more than one
level at a time by absorbing or emitting
enough energy. An electron cannot jump
to a spot midway between levels (n ≠ 2.5)
 We no longer have an
atom. We have an ion,
since the atom has lost
an electron.
Need for a Better Model
 Bohr’s model has some limitations.
 It worked very well for hydrogen (the simplest
atom with only 1 electron). It allowed scientists to
make detailed calculations that explains the
behavior of H.
 It didn’t work for other elements, mostly because
the calculations were so detailed and complex they
couldn’t be done (the math hasn’t been invented
 It also violated the Heisenberg Uncertainty
Principle. But no one knew that yet! We’ll get to
Heisenberg Uncertainty Principle
Since momentum = mass x velocity
and since the mass of the electron is
known, for all practical purposes, the
Heisenberg Uncertainty Principle
says that you can’t know both the
position of the electron and the speed
of the electron, at the same time.
 The Heisenberg
Principle states that
for a very small
particle, such as an
electron, you cannot
know both its exact
momentum and its
exact position at the
same time.
So why does Bohr’s model
violate Heisenberg’s Principle
The Modern Model of the
 Many scientists (Louis DeBroglie, Max Planck, Albert
Einstein, Erwin Schroedinger, and many others) worked
on the model of the atom.
 Actually, they weren’t working on the model of the
atom. They were just working on cool and interesting
scientific problems. But they all made contributions to
our current understanding of the atom.
 Quantum mechanics is the “modern” model of the
atom. By the early 1930s, it had been “born.” It’s the
model we still use today.
Gee, bet this
guy never
amounted to
Photoelectric Effect
 The photoelectric effect
was discovered by
Albert Einstein.
 He found that light of a
certain energy could
“knock electrons loose”
from certain metals.
 Oh BTW, Einstein
published “Theory of
Relativity” 6 years later.
Wait! Light Knocks Electrons Off
of Atoms, if it has Enough Energy?
 Alkali metals seem to be very prone
to this, if the light is of a sufficient
 Einstein called this the photoelectric
effect. In this way, light is behaving
not as a wave but as a particle.
Photoelectric Effect, So What?
 Anyway, you might not be terribly
impressed with Einstein’s discovery.
 However, if electrons can be pried
loose from the metal, they can move
 If they can move around, the
movement of electrons can generate a
small amount of electricity.
 If you can capture this electricity, you
can do useful work.
Solar Power
 Solar power is based off of this principle. A
photoelectric cell is constructed which has a
certain type of metal in it.
 When sunlight shines on it, some of the
electrons are pried loose.
 The cell generates an amount of electricity.
 With hundreds or thousands of these in series,
you can take a small amount of power
generated in each cell, and multiply that by the
total number of cells, and use that generated
power to do work in your house.
OK, well so what?
 This was one of the assumptions that
helped lead scientists to quantum
 While in graduate school in France, a
young scientist named Louis de
Broglie asked himself this question
 If light can act as a particle, can a
moving particle also act as a wave?
De Broglie Equation
 The answer was yes.
 λ=h/mxv
 λ = wavelength
 h = Planck’s constant
 m = mass
 v = velocity
 The wavelength for a baseball pitched at 90
miles per hour, calculated using de Broglie’s
equation is 8.2 x 10-38 meter.
 We have no measuring instrument capable
of detecting such an incredibly small
The Final Pieces of the Puzzle
 But, electrons have masses which are much, much less, and they
have wavelengths which can be measured much more easily.
 So if particles could act as a wave, and electrons are particles,
would it help our understanding of the atom to think of
electrons as “waves?”
 The answer was yes and quantum mechanics was the result.
 Previously, scientists had treated electrons just as particles, and
tried to use all the normal math techniques that they used on
particles they could see. Those techniques worked well with
large particles, but with electrons, not so much.
Quantum Mechanics
 When Erwin Schroedinger
recalculated everything using the
“wave math” everything started to
come together and make total sense.
 He called this quantum mechanics.
 Later in life, he actually said this
about quantum mechanics…
 “I do not like it and I regret having
had anything to do with it.”
 To which I add, ditto!
His simple-looking
but really complex
math equation.
Still the best model we
Quantum mechanics
has been around for 80
years now.
It still predicts the
behavior of atoms well,
and we haven’t found
anything better.
If anyone ever finds
anything better, I’ll let
you know
Had Dinner with this Dude
Dr. Glenn T. Seaborg
 That was 2,400 years of
history in one lesson!
Discovered Plutonium in
1940; won Nobel Prize in
1951; predicted the
existence of the actinide
series; had dinner with Mr.
Schwartz in 1981; element
106 named in his honor in
1997 (Sg); died 1999.
 There’s lots more to
know and explore.
 Yes, you need to know
the important people
and what they did. It
could be on the SOL!
The End
Next: Chapter 5 powerpoint…

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