HISTORY OF CHEMISTRY
Cave paintings 20,000 BP.
Pottery 8000 BP.
Fire by friction produced 7000 BP.
Copper hammered into shape 6000 BP.
Civilization began 4000 BP.
Native copper collected 9000 BP.
In Egypt gold was mined and processed by slaves.
Sumerians 3000 BP discovered smelting = heat metal with dirt/stones
(metal ores).
bronze = copper + tin.
Iron oxide improved copper smelting by acting as a flux.
Iron known in Egypt 3000 BP - metal of heaven - from
meteorites.
Iron is softer than bronze. Heating iron in presence of carbon
increases strength of iron = carburizing (steel). Made by
Hittites in 1200 BP.
Action of bacteria on nitrogenous waste (urine) = niter or sodium
nitrate/potassium nitrate. Niter ingredient of gunpowder.
Ethanol production (fermentation) 10,000 BP. Eethanol is used as extractant for organic materials. Organic end of ethanol mixes well with plant material. Alcohol end of ethanol mixes well with water.
Early physicians.
Pigments and dyes.
Glass formed from fused silicates created naturally by lightning
strikes, volcanoes, meteorite strikes. 3000 BP in Mesopotamia -
glass = sand/quartz + sodium carbonate. 1300 BP glass =
sand/quartz + calcium carbonate (in shells/limestone/chalk).
Mummification = steeped body for 70 days in natron bath (sodium-aluminum-silicon-oxygen salt). Killed bacteria that cause decomposition and dehydrated cells so future bacteria would not
flourish. Then sealed from moisture and air.
Explanations for the observed world > Greek philosophers.
Babylonians developed sophisticated math 1600 BP.
Empedocles of Agrigentum (c. 495-435 B.C.) proof by physical means that air is
a material body. Using a water clock (cone with holes at the
bottom and top, which when placed in water sinks slowly to the
bottom). When finger placed over opening at top of clock water
would not fill the cone. When removed finger air rushed
out.
Distillation
sublimation (solid to gas with no liquid phase)
fusion (melting)
solvation (dissolving)
filtration
crystallization
calcination (heating to high temperature without melting)
usually resulted in oxidation (incorporating oxygen from the
air)
Refine gold by using mercury (gold pulled from ore into Hg, Hg is
then driven off by heat leaving behind the pure Au).
Alexandrian alchemist known as Miriam, Maria or Mary the Jew
introduced the water bath.
"Greek Fire" = quicklime (Calcium oxide from heating limestone or
shells generated heat when combined with water. If quicklime and
petroleum are exposed to water the heat can ignite the
petroleum.).
1200s universities were founded in Naples, Paris, Oxford,
Cambridge, Seville and Siena.
1200s writings attributed to Ramon Lull authors
used letters of the alphabet to symbolize alchemical principles,
materials and operations and arranged them in tables
recipes
were given or combinations of the letters.
Since prehistoric times people had fermented alcoholic
solutions
ethanol is flammable in its pure form
salts added
to distillation vessel pulled water from the alcohol©water
mixture.
Paracelsus (1493-1541) subjected a large number of metals
to a standardized set of procedures and obtained a series of
salts. First to use word alcohol to describe distilled
ethanol. Used mercury to treat syphilis. Idea that doctors
should act on what they observe rather than blindly following
accepted authority.
1450 invention of movable type. Chemical knowledge was
standardized. It was available in greater quantities and at a
much lower price.
1540 first printed book on metallurgy and metallurgical chemistry
by Vannoccio Biringuccio (1480-1539) became a standard reference for metal
workers in the 1600s.
Georgius Agricola (1494-1555) wrote on methods of geology
and mineralogy. Emphasized individual experimentation and
observation. Used as a reference for over a century.
Alchymia considered the first chemistry textbook by Libavius b. ~1560 is a clear and highly systematic
survey of contemporary descriptive chemistry. Four parts to
book:
- techniques and equipment
- chemical preparations
- chemical analysis
- theory of transmutation
May have been the first directions for making hydrochloric acid by
heating saltwater in the presence of clay. May have been first to
show that sulfuric acid can be made by burning sulphur with niter
(potassium nitrate).
René Descartes (1596-1650) and Francis
Bacon (1561-1626) proposed that truth can only be arrived at by careful,
stepwise analysis and with a review at each step for oversight
(this was revolutionary).
Hg is well known for its combining powers.
Johannes van Helmont (1577-1644) made
extensive use of the balance and as a result of his careful
observations he was convinced that nothing is created or destroyed
in a chemical reaction. In willow tree experiment he weighed a
willow tree seedling and then planted in a tub with 200 lbs of
soil. At the end of 5 years he found that the tree had increased
in weight but the soil weighed the same. Therefore concluded that
the tree had converted the water into wood. Helmont coined the
word gas (probably based on chaos).
Angelus Sala (1575-1640) was able to show the he could
artificially produce a hydrated copper sulfate identical to a
naturally occurring substance.
Robert Boyle (1627-1691) reported in his book that sound
did not propagate in a vacuum and that air was necessary for life
and flame. His assistant Robert Hooke built an air pump. Boyle's
Law = volume of air was inversely proportional to the pressure
applied. Boyle also made systematic studies of reactions between
acids and bases. Application of plant derived acid and base
indicators. Boyle observed that air had something to do with
combustion.
Robert Hooke (1635-1703) and Hook's Law = stretching in an elastic body such as a spring is
proportional to the force applied.
John Mayow (1641-1679) showed that gas could be transformed
from one vessel to another under water and that volumes of gas
could be directly compared if they were at the same pressure. Two
parts to air: first part that supported combustion nitro-aerial.
Weight gained by metals during calcination due to absorption of
nitro-aerial particles.
Joseph Black (1728-1799) concluded that combustion,
respiration and fermentation all produced the same gas and that it
did not support life. We now know that this gas is carbon
dioxide
Black rejected the idea of four elements saying instead
that materials should be separated into classes.
Joseph Priestley (1733-1804)invented soda water = when
carbon dioxide dissolved in water it produced a pleasant
drink. Also discovered that rubber from South America, called
India rubber, efficiently erased pencil marks. Measured volume of
"goodness" of air for respiration rather than using mice. In August
1774 Priestley prepared oxygen by collecting the gas given off when
mercuric oxide is heated. Made carbon monoxide by passing steam
over glowing charcoal. When sparked hydrogen with common air he
found water.
Henry Cavendish collected hydrogen from metals
treated with acid.
Mikhail Vasilevich Lomonosov (1711-1765) saw no necessity
for phlogiston. He heated metals in air-tight vessels and found
no increase in the weight of the system. Therefore something from
air combined with the metal.
Antoine Laurent Lavoisier (1743-1794) did experiments on
conservation of mass. Distilled water was heated in a glass
container for 101 days. At end there was no change in
weight. Also made the pronouncement that water was not an element as previously thought but the combination of oxygen with an
inflammable principle which he named hydrogen from the Greek for the begetter of water.
Lavoisier and Laplace (1749-1827) developed a calorimeter, a device for
measuring heat released during respiration and combustion and
concluded that respiration was a form of combustion.
Lavoiser asserted that calcination was a combination - oxygen with
metal and that reduction was a separation - oxygen from
metal. Said oxygen was not a variety of the element air but a
separate substance and that phlogiston did not exist (broke the
Aristotelian barrier of four elements).
Louis Bernard Guyton de Morveau (1737-1816), Bertholle, Antoine Francois de Fourcroy (1755-1809) and Lavoisier developed a new
system of nomeclature that named compounds according to elements
they contain and their functionality.
Berthollet - beginnings of law of mass action whereby the relative mass of
reactants and products determined the direction of the
reaction. found evidence for the reversibility of reactions. He
also developed a chemical bleaching process that used chlorine
absorbed in sodium hydroxide solution.
Joseph Louis Proust (1754-1826) - each chemical compound
has a fixed and invariable composition by weight i.e. each compound
has a formula = law of definite proportions (some metal oxides and sulfides do have compositions that vary over a narrow range >in
modern materials science and inorganic chemistry these are called
berthollides).
John Dalton (1766-1844) reintroduced a systematic atomic
theory based on the elements of Lavoisier (the atoms had
characteristic masses (atomic weights) and combinations of these
atoms in fixed ratios made up the range of chemical compounds)
>tendency of materials to combine in simple whole number
ratios. The first direct evidence for atoms became known as the
law of multiple proportions. Dalton also derived a scale of
atomic weights. He arbitrarily chose the wight of hydrogen to be
1. For the first time it allowed chemists to interpret mass
relationships rationally.
Democritus of Abdera (c. 460-370 B.C.) postulated atoms in pre-Aristotelian
Greek philosophy.
Atoms were proposed by Descartes and Hooke.
Jeremais Benjamin Richter (1762-1807) (a forerunner of
Dalton) proposed that chemical processes are based on
mathematical laws and had coined the word stoichiometry to describe
mass ratios of chemical elements in reactions.
Electricity
Force that held atoms together: chemical affinity (based on
electrical attraction)
Greek's knew how to generate static electricity by rubbing amber
with wool (elektron is the Greek word for amber).
Otto von Guericke made a machine for generating
a high potential electric charge in the 1500s.
Leiden jar for storing static charge was invented in 1745 by Pieter van Musschenbroek.
In the 1750s Benjamin Franklin and kite
experiment in which he collected a charge from a thunder cloud in
a Leiden jar.
Alessandro Volta (1745-1827) built first electrochemical
cell (electricity-generating pile).
William Nicholson (1753-1815) discovered electrolysis = the decomposition of materials by
electricity.
Jöns Jakob Berzelius (1779-1848) repeated experiments that
electricity split water and also electricity split salts and also
used electricity to isolate calcium and barium. Also recognized that Cl, Br and I all belonged to the same chemical
family which he called the halogens. Used term isomerism to indicate substances with the same chemical
composition but different physical properties. Used term catalysis.
Used term allotropy = certain elements exist in different solid
forms with different properties. Began practice of writing chemical formulas using first letter of
element to stand for the atom of the element (adding a second
letter to distinguish between two elements beginning with the same
first letter). Also used superscripts to indicate their relative number in the
compound (today use subscripts).
Between 1790 and 1848 approximately 29 new elements were
discovered.
Humphry Davy (1778-1829) tried to show that heat was not a
material but a mode of motion. Proposed the use of nitrous oxide
(laughing gas) in minor surgical operation, it achieved its first
success as a recreational drug. Improved Volta's battery design by
putting zinc and silver plates directly into acid and connecting
them with wires and showed that passing current through a salt or
acid broke it down moving part of the material toward the negative
pole and part toward the positive pole.
Michael Faraday (1791-1867). He read "The Improvement of
the Mind" which suggested keeping a notebook of ideas and
observations. Found that the amount of chemical decomposition in a
solution is proportional to the amount of electricity passing
through it. Found that the mass of material deposited at an
electrode by a given amount of current is proportional to the
atomic mass of the material divided by its charge. Concluded that
electrolysis (the decomposition of material by electricity)
occurred when electricity flowed through solutions and he called
the electrically charged fragments ions, from the Greek word for
wanderer. Also demonstrated the rotation of a current-carrying wire
around a magnet and of a magnet around a current-carrying wire. Faraday also proposed that the electric force was a field.
Hans Christian Oersted showed an interaction
between electricity and magnetism when a wire carrying an electric
current caused a nearby magnetic needle to move.
Joseph Louis Gay-Lussac (1778-1850) and Alexander von
Humboldt found that two volumes of hydrogen combined with one
volume of oxygen to contract into one volume of water measured as
a gas.
Amedeo Avogadro (1776-1856) law that equal volumes of all
gases contained an equal number of molecules (under like conditions
of pressure and temperature).
With the industrial revolution it was found that heat from
combustion could produce work.
Benjamin Thompson, Count Rumford (1753-1814) concluded that
heat was not a material substance since when drilling metal and
stopped the heat did not stop when drill was stopped
Temperature is a measure of translational energy >the energy with
which moving particles strike the thermometer.
William Thomson, Lord Kelvin (1824-1907) observed a
regularity in the behaviour of fixed amounts of different gases.
When pressure was plotted versus temperature for various gases, the
lines, extrapolated back to zero pressure all converged at -273.15
C. The temperature was absolute zero. Also used the term thermo-dynamic.
Herman von Helmholtz (1821-1894) : the first law of
thermodynamics (energy is conserved). Second law of thermodynamics
arrived at by Lord Kelvin (Rudolf Clausius described it as saying
"the entropy of the world strives toward a maximum".
Ludwig Boltzmann (1844-1906) used statistical analysis to
show that entropy is a manifestation of the natural tendency of a
system to seek the state of maximum disorder. The disordered state
was the natural state because it is the state with the highest
probability.
Walter Nernst (1864-1941) third law of thermodynamics s =
k log W (carved on his grave)
Josiah Willard Gibbs (1839-1903) saw that he calculated
charge in entropy for the system and surroundings predicted the
direction of spontaneous change in any chemical reaction. Derived
a phase rule for determining whether or not a chemical mixture was
in equilibrium and what components or conditions could be varied
without pushing it into another phase. Phase diagrams.
James Clerk Maxwell (1831-1879) gas viscosity should be independent of its density. Also that gas particles do not all
travel at the same speed.
Henry Louis Le Châtelier (1850-1936) found that equilibria
could be shifted by adding or subtracting heat. Principle: when a
strain is place on a system in equilibrium there is a readjustment
in the direction that most effectively relieves the strain. This
strain could be in the form of material or heat.
Now a chemist could show with Gibbs function whether or not a
reaction would occur spontaneously if it did not, how it could be
coaxed in the desired direction using Le Châtelier's
principle.
Friedrich Wilhelm Ostwald (1853-1932) founded the new
discipline of physical chemistry.
(blood from people in tropics is more oxygenated (redder) because
less oxygen is burned to produce needed heat in body).
Organic Chemistry
The ability of carbon to form chains allows carbon to make up the
complex materials of life.
Estimated that the human body contains 5 million different organic
compounds and a single bacterium contains 5000 different organic
compounds.
Materials extracted from plants and animals are organic
compounds
- herbs used for medicine
- ethanol for mood control
- acetic acid from sour wine
- lactic acid from milk
- citric acid from lemons
- formic acid from ants
Friedrich Wöhler (1800-1882) and Justus
von Liebig (1803-1873) discovered that two different chemicals had the same
elements present in the same ratios - cyanic acid, fulminic acid and
later isocyanic acid. It is now know they have different chemical
behaviour because of different arrangement of elements in the
compounds. Research groups headed by a senior scientist as mentor
and junior scientists as lieutenants and students are a Liebig
creation.
Berzelius proposed name isomerism the describe
materials with the same chemical composition but different
properties prior to Wöhler-Liebig.
Wöhler for the first time a natural product was made from inorganic
chemicals. In an attempted synthesis of ammonium cyanate found had same composition
as urea (the ammonium salt of cyanic acid) from urine.
Jean Baptiste André Dumas (1800-1884) came up with concept
of an "organic radical" = a group of elements within an organic
compound that functioned as a unit.
Robert Wilhelm Bunsen (1811-1899) invented gas burner
called the Bunsen burner.
(amines responsible for fishy smell of decomposing seafood)
Auguste Laurent (1807-1853) his research in chlorine
substitution led him to the nucleus theory (compounds were made of
nuclei (radicals) in which substitution could take place).
Charles Frédéric Gerhardt (1816-1856) devised a
classification scheme that grouped compounds with similar
reactivity but differed by the number of carbon atoms that formed
them (homologous series) i.e. functional groups.
Edward Frankand (1825-1899) when studied combinations of
organic materials and metals (organometallics) he noticed that
there seemed to be "a fixity in the maximum combining value". This
fixed maximum combining value or "valence".
Archiblad Scott Couper (1831-1892) in 1858 wrote paper that
probably contained the first statement about the tetravalence of
carbon and its chain-forming ability.
Friedrich August Kekulé (1829-1896) visualized the chemical bond
as a lumpy cloud (referred to as "Kekulé's sausages") joining atoms.
Other scientists preferred to represent bonds by a straight line.
Also came up with name aromatic for the generally pleasant smelling
class of benzene-based compounds and came up with the ring
structure of benzene.
Jean Baptiste Biot (1774-1862) a crystallographer was the
first to observe optical activity in light passing through liquids
or solutions of natural products like turpentine.
Louis Pasteur (1822-1895) examined crystals of racemic
sodium ammonium tartarate under a magnifying glass and found that
one half had a particular crystal face oriented to the left and the
other half to the right.
Jacobus Henricus van't Hoff (1852-1911) and Joseph Achille Le Bel (1847-1930) separately developed the
idea that the light-rotating power of compounds (optical activity)
was due to their three-dimensional arrangements in space.
Dmitri Ivanovich Mendeleev (1834-1907) discoverer of the
periodic table in paper published in 1869. Systematized elements.
Left gaps for elements he suspected were missing.
Improvements in equipment: better balances, optical glass, furnaces etc. led to sorting out of rare earth elements which have nearly identical properties.
Spectroscopy
Ancient texts of India report use of flame color in chemical
analysis. Later chemists used flame colors as their only way of
distinguishing sodium and potassium salts.
In 1800s discovered that elements in flames have spectra that show
characteristic line patterns and these line patterns can be
measured and catalogued.
Robert Bunsen needed a colorless flame to analyze flame colors of
salts in mineral waters so he invented the Bunsen burner.
Robert Bunsen and Gustav Robert Kirchhoff
(1824-1887) invented spectrometer and identified new elements cesium and
rubidium by showing that these new elements produced line spectra
that were unique.
William Crookes (1832-1919) analyzed an unknown gas and
realized that its lines matched lines observed in spectrum of the
sun. This element was helium (named for the Greek helios for the
sun).
Joseph John Thomson (1856-1940) showed that cathode rays
were composed of negatively charged particles that had one-thousandth the mass of a hydrogen atom.
Thomson and Kelvin modeled the atom as a mass of positive charge
interfused with imbedded electrons.
Wilhelm Konrad Rontgen (1845-1903) discovered x-rays in
1895.
Marya Sklodowska Curie (1867-1934) found that
pitchblende was more radioactive than its uranium and thorium
content could account for and Marie and Pierre
Curie (1859-1906) found polonium and radium by dissolving minerals (ores) in acids, precipitating different
fractions with reagents such as sulfates and hydroxides,
redissolving the precipitates and crystallizing and recrystallizing
the products on a huge scale from 1898-1902. Pierre and Marie refused to patent their materials, preferring to
make them available to all who wished to use them.
Ernest Rutherford (1871-1937) studied uranium and showed
that it gave off at least two types of particles: positively
charged nuclei of helium atoms called alpha radiation and highªspeed electrons called beta radiation. Rutherford did experiments
in which high-energy particles passed through gold foil but some
bounced back. From this came new model with negatively charged
electrons in huge orbits circling a tiny, dense, positively charged
nucleus. (Now know mass of atom is mainly in the nucleus which has
a density of 1,000 trillion grams per cubic centimetre). Paradox
that an electron circling a nucleus should emit radiation and
emitting radiation it should lose energy and spiral into nucleus
>Bohr refined this model.
Henry Moseley (1887-1915) showed by analysing x-ray spectra
that the positive charge of each element's nucleus increases by one
as traverse periodic table. He called this the atomic
number.
(a pure solvent flows into a solution because the mixture is more
disordered than the pure solvent and this drives the osmotic
flow).
Svante August Arrhenius (1859-1927) proposed existence of
permanent ions in solution to explain anomalously high freezing
points and low boiling points seen in salt solutions.
(hemoglobin and chlorophyll are coordination complexes)
Alfred Werner (1866-1919) the founder of coordination-complex chemistry. Proposed a coordination number that was the
preferred number of ligands that a given metal atom sought to
acquire.
The term biochemistry appeared around 1910.
Chemists attempted to synthesize natural compounds with medicinal
activity. William Henry Perkin (1838-1907) was looking for
quinine when he found mauve dye.
Felix Hofmann prepared acetylsalicylic acid
from salicylic acid and the anhydride of acetic acid. Bayer called
this aspirin (aspirin decomposes in moist air to acetic acid, the
acid found in vinegar).
Louis Pasteur showed that fermentation is
accompanied by the growth of yeast. Also showed that microorganisms
were present in the air and water. Also showed that when
microorganisms were destroyed, as by heat, the media were preserved
(now know as pasteurization). Argued that many diseases were caused
by microorganisms.
Joseph Lister actively sought disinfectants to
use against microorganisms. Introduced carbolic acid (phenol) as an
antiseptic for sterilizing instruments and wounds. Reduced
mortality from amputations dramatically from their prior 50
percent.
Pasteur looked for sources of dead bacteria that could be used to
trigger immunity and protect against live bacteria. Used these
methods to protect sheep from anthrax and people from
rabies.
Fredrick Accum (1769-1838) in 1820 raised questions about
saftety of prepared foods. This stimulated a public demand for
purity in food and this demand along with others from industrial
and medicinal chemistry stimulated the growth of analytical
chemistry.
Growth in industry promoted the growth of analytical chemistry and
biochemistry and the analytical chemist and the biochemists
promoted industrial growth.
Public awareness of microorganisms increased the demand for
soap.
One of the first pieces of environmental legislation, the British
Alkali Act, that required soda manufacturers to run their gaseous
waste through acid-absorbing towers.
Alfred Nobel (1833-1896) succeeded in stabilizing
nitroglycerine by absorbing it in sawdust or diatomaceous earth and
he named the new explosive dynamite (in reference to its dynamic
force).
(chemistry could not progress without physics)
Chaim Weizmann (1874-1952) developed a fermentation process
that produced acetone which was needed in preparing smokeless
powder during World War I.
Wilhelm Ostwald worked out conditions for
reacting air and water with ammonia to make nitric acid needed for
explosives.
Fritz Haber (1868-1934) made synthetic ammonia by combining
nitrogen and hydrogen under pressure using iron as a catalyst.
Haber also studied possibility of using chemical gases in
combat.
Chlorine used by Germans on April 22, 1915 during the battle of
Ypres in Northern France. France countered with phosgene (severe
respiratory irritant) at Verdun in February 1916. Germans
countered with dichlorodiethyl sulfide (attacked skin as well as
lungs) in July 1917. Under Article 297 of the Versailles Treaty
Germany lost many of its chemical patents (such as aspirin) and
this caused a chemical redistribution of wealth.
Gilbert Newton Lewis proposed octet rule (ions
or atoms with a filled layer of eight electrons have a special
stability). Also proposed that an atom tended to form an ion by
gaining or losing the number of electrons needed to complete an
octet. Lewis structures are still taught today as the most
intuitive way of envisioning simple structures and bonding.
Alfred Parson suggested that a chemical bond
results from two electrons being shared between two atoms.
James Clerk Maxwell discovered that light is an
oscillating electromagnetic wave. A moving electric charge
generates a magnetic field and the magnetic field generates an
opposing electric field and the opposing electric field generates
an opposing magnetic field and so on, with each field pushing the other out of the way. Maxwell calculated the speed at which this
occurs and found it to be at the speed of light. Maxwell's
conclusion was confirmed experimentally by Heinrich Hertz (1857-1894).
Max Planck (1858-1947) assumed that light was not
continuous but came in discrete packets called quanta and that the
size of these packets became larger at shorter wavelengths.
Albert Einstein (1879-1955) saw that minute particles suspended in
liquid are in constant motion called Brownian motion. It can be
seen under a microscope. Einstein extrapolated the motion to the
molecular level to show that it arises from buffeting by
molecules. Thought about theory of relativity. Also explanation for the photoelectric effect based on Planck's quanta.
When light of the proper frequency shines on certain metals it can
cause an electron flow from the metal surface. For electrons to be
ejected from the metal the light has to have greater than a
particular frequency (ie. quanta of a minimum energy are
needed).
Niels Bohr (1885-1962) felt that Planck's quantized
energies were related to the discrete lines of elemental spectra
and to the planetary model of the atom. In Bohr's theory, electron
orbits, or energy levels are given numbers, called quantum numbers:
the principal quantum number defines the shell in which the
electron is located; the second quantum number is the angular
momentum; and the third quantum number. The fourth quantum number
explained by George E. Uhlenbeck and Sam A. Goudsmit whereby
electrons could be thought of as spinning on an axis (for this to
be literally true the electron would have to spin at then times the
speed of light, but the model worked well).
Wolfgang Pauli (1900- ) the Pauli Exclusion Principle:
there can never be two equivalent electrons in an atom for which
the values of all the quantum numbers are the same i.e. no two
electrons can have the same coordinates. This explained the
periodic build up of elements. Electrons go into the lowest
unfilled energy level. This was given the name Aufbau (build-up)
principle by Bohr.
Arnold Sommerfeld (1868-1951) proposed subshells within the
principal energy level. Bohr proposed three possible orientations
for orbits: parallel, antiparallel or perpendicular to a defining
magnetic field. Resulted in groups of elements with similar
reactivities have the same electron configuration ie. they have the
same number of electrons in the same types of outer orbits and
subshells. However Bohr's model was exact only for hydrogen.
Louis Victor Pierre Raymond de Broglie (1892- ) his idea
was that if light behaved as a wave or a particle then why could
not a particle, lie an electron, behave like a wave?
Erwin Schrödinger (1887-1961)
Werner Heisenberg (1901- ) and the Heisenberg
uncertainty principle: the position and momentum of an electron
could not be computed at the same instant in time.
(the energy of UV light is sufficient to knock the tiny electron
around which is what UV light does to electrons in your skin when
you sunbathe)
Max Born (1882- ) said that Schrödinger's waves were
probability waves.
Walter Heitler and Fritz
London (1900-1954) applied quantum theory to develop the first quantitative
model of a chemical bond. They found that two electrons sharing a
space between two nuclei were attracted by both nuclei and this
lowered the energy of the system as a whole. Two hydrogen nuclei
formed a bond because a bond minimized electrostatic interactions:
the two positive nuclei were drawn together by attracting each
other's negative electron cloud but only until this attraction was
balanced by the repulsion of like charges.
Linus Pauling used x-ray diffraction to study
bonding in crystals. Developed a model for bonding called the
valence-bond approach which assumed that orbitals were formed in
molecules by the overlapping of atomic orbitals. Also used hybrid
atomic orbitals. Also used the notion of resonance.
Robert S. Mulliken developed with Frederick
Hund the molecular-orbital system: a bonding model based on
orbitals that extended over the entire molecule. These molecular
orbitals were numbered as were atomic orbitals and electrons in
them had various quantized amounts of angular momentum, magnetic
moment and spin. Notation for diatomics (molecules with just two
nuclei): s (sigma), p (pi), d (delta), f (phi) were analogous with
the atomic s, p, d and f orbitals. Whether or not the molecule is
stable depends on how many electrons are in bonding versus
antibonding orbitals. Reactivity is based on the shapes of occupied
molecular orbitals.
(an extensive library of calculated molecular orbitals has
accumulated)
Spectroscopy (interactions of molecules with light)
Hydrogen takes light in the IR range to excite changes in
vibrational levels. Hydrogen takes light in the microwave region to
excite changes in the rotational levels.
The quantization of frequency changes of scattered light was
described by Chandrasekhara Venkata
Raman.
Lewis coined the word photon to denote a quantum or packet of light. Studied photochemistry and found two types of
photoluminescence:
i) phosphorescence (excited electron spin parallel to spin of remaining ground state electron
ii) fluorescence (spin antiparallel to ground state electron.
World War II caused European scientists to relocate worldwide. War caused shortage of rubber. Tried to make synthetic rubber.
Rubber like many other biological materials is a polymer made up of
chains of monomers (the same or different molecules). Polymer
properties depend on the monomer, the length of the chain and on
the branching of the chain.
In the 1920s Joseph Patrick invented
polyvinylchloride (PVC). Others invented polyethylene, polystyrene,
Lucite and Plexiglass (organic glass).
Wallace Hume Carothers (1896-1937) tried to understand the
composition of natural polymers such as rubber, cellulose, and silk
and then to imitate them. He was boss of the team that invented
nylon.
Dacron (a high-melting and insoluble polyester) was developed by Rex Whinfield and James T.
Dickson.
Teflon was discovered by Roy J. Plunkett.
Teflon was inert to acids, bases, heat and solvents and very
slippery.
Go to History of Chemistry - Part 2