Chemical History

A Quick History of
With thanks to Isaac Asimov
 1i—construction and defense of a scientific viewpoint
 2i—historical and quantum models
 Chapter readings
 5, section 1
 13, section 1
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 Greeks
 Aristotle suggested that everything was composed
of 4 elements:
 Water, Air, Earth and Fire
 He later added a 5th element which he called
“aether” which the stars and the heavens were
made from.
 Click on the next slide to see three of these
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…
Democritus—400 BC
Democritus was the first to suggest
that matter was composed of
atoms, which he called “atamos”
meaning “indivisible.”
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
The Alchemists
Roger Bacon was an English alchemist who may
or may not have been the first European to invent
gunpowder. Some credit him; some say it was a
German guy. I always thought the Chinese did
thousands of years ago.
Alchemists actually discovered some chemistry,
but much of their work was to turn other thing,
generally lead, into gold.
This is called a “transmutation” reaction, and
cannot be done by chemical reactions.
However, in Chapter 28, we’ll learn about nuclear
reactions, and turning lead into gold is now
possible, but still isn’t profitable.
 The ancient Greeks were thinkers. They talked the
talk but didn’t walk the walk.
 The ancient Egyptians, on the other hand, were a
practical people and invented a lot of things. They
made the first glass, and dyes and medicines, for
 The Greeks called this “chemia,” after the Egyptian
word “Chem,” which also meant black.
 Chem was the Egyptians’ name for their own
 Some people thought that chemia meant “black
magic,” since some of the processes the Egyptians
were using seemed like magic.
 When the Arabs later conquered Egypt, they added
the prefix “al” which means “the.”
 So it became “al chemia”
 And later in English, it was called alchemy. And
that was appropriate because for a while, alchemy
was as much phoney-baloney magic as it was real
An Alchemist at work…
Paracelsus was a famous alchemist who
actually discovered salt in about 1530.
Salt had been known for thousands of
years, but he realized some of its
“properties” and was probably the first
person to realize that elements could
come together to form compounds,
which are totally different from the
elements they are made from.
Paracelsus also is credited with
discovering zinc. The alchemist in the
picture may or may not actually be
Paracelsus, but it’s a famous painting of
Robert Boyle
A 17th century British nobleman (the youngest
of 14 children born to the Earl of Cork). He met
Galileo and was an alchemist. Maybe the last
of the alchemists and the first one to be a “real”
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; in other
words, as pressure goes up, volume goes
down, and vice versa.
More on Boyle
 Boyle started calling himself a “chymist” because
the term alchemist had gotten a bad name. The
spelling was eventually changed to chemist.
 He questioned the old Greek notions of the
elements. He even did some experiments which
proved that water, still thought to be an element,
wasn’t an element at all, but actually a compound.
 Even in Boyle’s time, a few substances were known,
but they weren’t known to be elements yet.
 For example, gold and silver and copper and lead
were known since the ancient times, but they
weren’t known to be elements.
 It’s also thought that 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
 In the late 1700’s a French chemist changed all that.
He was Antoine Lavoisier, but first…
Phlogiston and Priestly
Phlogiston was a theory that explained how
things burned and what happened when they
Things that burned would release phlogiston to
the air (so-called phlogisticated air). When a
substance had used up all of its phlogiston, it
would stop burning. And if you could remove
the phlogiston from the air (dephlogisticated
air) things would burn again.
Joseph Priestley was a main supporter of this
theory. He also was the inventor of something
much more interesting: carbonated beverages,
specifically soda-water.
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 compound.
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
More on Lavoisier
 Lavoisier figured out that Priestley’s dephlogisticated air
made things burn, and he renamed this as oxygen.
 He also figured out that phlogisticated air was nitrogen
(sometimes, carbon dioxide was also identifed as
 He also replaced the phlogiston theory with a new
theory of combustion. He said that when something
burned it reacted with oxygen or was “oxidized.”
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 world.
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.
E. Goldstein
 German physicist Eugen Goldstein discovered the
proton in 1886.
 The proton is positively charged and determines the
identity of an element.
 The number of protons is a property called “atomic
number.” Each element has a unique atomic
JJ Thompson
In 1897, Thompson
discovered the electron.
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
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 neutral.
So, he proposed that the electrons were
randomly distributed throughout.
A little-known fact is that they weren’t just
sitting there. In fact, they were moving, and
Thompson proposed they were moving more
or less in a circular fashion within the
positively charged “rest of the atom.”
Ernest Rutherford
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.
Rutherford was from New Zealand, and like
his mentor, Thompson, also won a 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.
The Gold Foil Experiment
Check out the link!
Reference for below…
Rutherford created a device
to “shoot” αparticles 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!
The Nuclear Model
 Rutherford was completely surprised by this result.
 He had accidentally discovered the nucleus.
 Rutherford said 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.”
 We usually call Rutherford’s model the “nuclear
Neils Bohr
Rutherford’s nuclear model only really lasted for
about 3 years, before Neils Bohr (who, oh by the
way, also won a Nobel Prize for this) revised it
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.
Soccer goalie on Denmark’s
1908 Olympic team AND a
Nobel Prize winner!!
This doesn’t happen, and Bohr answered why. His
model is usually called “the Planetary model,”
because in his model, electrons “orbit” the nucleus
much as our planets orbit the Sun.
Bohr’s Planetary Model
But the electrons don’t just orbit
They actually exist 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.
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 caluclations were so detailed
and complex they couldn’t be done.
 It also violated the Heisenberg Uncertainty
Principle (but that hadn’t been discovered
yet). We’ll get to that.
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
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.
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.
More Heisenberg
check out Heisenberg on YouTube link on website
 You can know where it is, but you won’t know
how fast it is going. You can know how fast it is
going but you won’t know exactly where it is.
 Is that true for any “particle” or just for
 It is true for any particle, but for large particles
(and compared to an electron, even a grain of
sand is infinitely huge) the uncertainties are so
incredible small that it seems as if you can know
it’s exact position and it’s exact speed.
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.
Light Knocks Electrons Off of
Atoms, if it has Enough Energy
 Alkali metals (lithium, sodium,
potassium, etc) seem to be very
prone to this, if the light is of a
sufficient energy.
 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
 In the study guide, we calculated the
wavelength for a baseball pitched at 90
miles per hour, using de Broglie’s equation.
 And the wavelength for the baseball is 8.2 x
10-38 meter. Of course, we have no
instrument capable of detecting such an
incredibly small distance.
It’s all Starting to Come
Together Now…
 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 scientists started to use the
math techniques that they used with
waves, everything started to come
together and make total sense.
 Erwin Schroedinger finally made the
“connection” between deBroglie’s
work and Bohr’s work.
 He said that electrons weren’t
orbiting in certain orbits around the
nucleus, but instead described them
as being found in “certain geometric
forms around the nucleus.”
His deceptively
simple but really
complex equation.
 We’re going to call these areas where
we find electrons “atomic orbitals.”
A Magic Carpet Ride…
 Our little history tour took us from
Democritus in 2,400 BC through a
series of important discoveries (many
of which were Nobel Prize worthy)
to Quantum Mechanics, which was
developed and finalized in the 1930s.
 Quantum mechanics describes the
behavior of atoms very well, and so
we think it’s a good model.
The End
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