Download Early chemical arts

Early chemical arts
Chemical arts evolved in
the ancient world long
before any theories of
matter were formulated.
Copper Age Axe
Iron Age
Swords
As early as 8,000 years
ago, people in the Middle
East were smelting
copper by heating copper
ores with charcoal to high
temperatures. The use of
gold, bronze, tin, iron, and
lead would follow in time.
Empedocles
• 450 BC
• Proposed that matter
was composed of four
elements:
–
–
–
–
Earth
Air
Fire
Water
Ancient Greek ideas on matter
Democritus (c. 460–c. 370 B.C.)
proposed that matter was made of
discrete indivisible particles, after
his teacher pointed out that a
beach looks smooth from afar but
is really made of discrete grains of
sand. He called his particles
atomos, meaning "cannot be cut."
His ideas were largely ignored until
the scientific revolution of the 16th,
17th, and 18th centuries.
Aristiotle:Later, Aristotle
(c. 384–c. 322 B.C.)
popularized the idea that
all matter was made of
earth, air, water, and fire in
varying proportions.
According to this notion,
one should be able to
make gold from other
materials by adjusting the
ratios of the four elements
therein. His ideas
influenced alchemy and
protochemistry for 2,000
years.
Alchemists
• First people to perform hands on
experiments.
• Three main beliefs:
– Some elements could be changed into others
(such as lead or tin into gold).
– They could find a substance that would give
them eternal life
– They could produce a universal solvent that
would dissolve all other substances.
Sir Francis Bacon
• 1600s
• Developed new
knowledge about the
physical world
through use of the
scientific method
Robert Boyle 1627-1691
• Boyle investigated
gasses
• Found a law defining
the volume of a gas
based on pressure and
temperature
Boyle Re-Defines Elements
• Boyle (1627–1691) redefined an element to
be a substance that could not be broken
down into simple substances and questioned
the elemental nature of Aristotle’s
foursome.
• Boyle recognized that elements could be
combined to form compounds.
Antoine Lavoisier
• Late 1700s
• Defined the element as a pure
substance that cannot be broken
down
• Discovered and identified 23
elements
• Recognized that mixtures exist.
• Classified air as a mixture of
oxygen and some other gases.
Henry Cavendish
• Late 1700s
• Experimented by mixing metal
with acid, which produced a
flammable gas (hydrogen).
• He discovered that this gas
would burn in oxygen to
produce water.
John Dalton (early 1800s)
• Things they knew by Dalton’s time:
– Elements were defined as substances which
could not be broken down further by
chemical means. (Lavoisier 1775)
– There was a law of definite proportions
(elements for a given compound always
combined in the same ratio)
– There was a law of conservation of mass. (In a
chemical reaction mass is never created or
destroyed.
John Dalton
• Was born in 1766
• Was a school teacher and later
a University Professor
• Used pre-existing laws and
his own experiments to come
up with the first atomic theory
• Came up with the first
modern atomic theory
Dalton’s Atomic Theory 1808
• All matter is made up of small particles called
atoms.
• Atoms cannot be created or destroyed, or cut into
smaller particles
• All atoms of the same element are identical in
mass and size, but they are different in mass and
size from the atoms of other elements.
• Compounds are created when atoms of different
elements link together in definite proportions
Dalton’s Billiard Ball Model
• The atom, according to Dalton, was much
like a tiny billiard ball.
• An element is a substance made up of
many very tiny particles (or many tiny
billiard balls) which are all identical.
• You could physically cut large chunks of
element into smaller pieces (like cutting
small chips of Iron off an anvil) but you
could not chemically break that element
apart
J.J. Thomson (1904)
• Joseph John Thompson was
born in 1856
• Was a top student in
mathematics and physics
• Ended up as head of Physics at
Cambridge University in
England
• Presided over a very
productive physics department
that produced 7 Nobel prize
winners
Thomson’s Plum Pudding Model
• Thompson reasoned that because
the gases in the tube were neutral to
start, there must be a balance of
charge in an atom
• Since he had no way to detect the
proton, he reasoned that the atom
was much like a plum pudding.
• The negative electrons were like
plums floating in a pudding of
positive charge.
• These charges were exactly equal in
a neutral atom
Ernest Rutherford
• Ernest Rutherford was born in 1871 in
New Zealand and had 11 brothers and
sisters.
• Graduated from Canterbury College in
Nelson NZ first in his class.
• Was awarded a trinity scholarship in
1895 to study at Cambridge under J.J.
Thompson.
• In 1897 he took up a chair as head of the
physics department at the McGill
University in Montreal
Discovering the Nucleus
• In 1911, through the results of his “Gold
Foil” experiment, Rutherford discovered the
atomic nucleus.
• The alpha ( α ) particle is a positively
charged, dense particle, equal to the nucleus
of a helium atom (+2)
• Rutherford fired these particles at an
extremely thin sheet of gold foil.
The Gold Foil Experiment
•Using the Thompson model, Rutherford thought that all the
positive alpha particles should pass straight through the foil
•In actuality a few of the particles were deflected,
while some shot directly back toward the source of
the particles!
A new Atomic Theory
• Rutherford’s deflected alpha
particles meant that there must
be an extremely massive, tiny
positively charged nucleus
inside the atom.
• It was these positive Nuclei
that were deflecting the
particles
• He proposed that the much
lighter electrons rotated around
this nucleus.
• This became known as the
Planetary Model.
The Neutron
• Protons accounted for only about half the total
mass of the gold atom
• Rutherford inferred that there must be something
similar in mass to the proton, but neutrally charged
inside the nucleus
• In 1930, the existence of the neutron was proved.
• The force of the neutron prevents the repulsion
between the protons from pushing the nucleus
apart.
Neils Bohr
• Bohr used the fact that
elements, when excited (by
heat or electricity), emit
characteristic spectra.
• For instance copper will glow
greenish blue, while
aluminum will glow white
• This fact had been known for
millennia by fireworks
makers.
Bohr’s Conclusions
• After studying the spectra of
the simplest elements, Bohr
refined the Rutherford
model
• The Bohr/Rutherford model
is still a planetary one,
however law’s about how
the electrons behave were
defined.
The Bohr Model
• Electrons are found only in
very specific energy levels
inside the atom. (also known
as orbitals or shells)
• When excited, the electrons
jump to higher energy levels
• Electrons may also lose
energy and fall to lower
energy levels
• Photons of certain
wavelengths are emitted when
the electrons decrease in
energy.