Title page:
Evolution of Modern Chemistry
R. Farmer
School of Chemistry, Bristol University
Reference:http://www.imax-wien.at/schulinfo/geheimnisse/images.jpg
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introduction
early discoveries
Greek khemeia
Egyptian Khemeia
Arabic al-kimiya
European alchemy
17th century
18th century
19th century
20th century
Introduction
Early applications of science date back to primitive humans, who discovered
how to manipulate fire for their own benefit. We had already become
practicing chemists. From this point onwards, man quickly experimented with
the world around him, developing a practical knowledge of chemistry.
Principle interests in ancient societies were metallurgy, pottery, dyes and
medicine. All of these were developed with considerable enthusiasm and skill,
even without a basic understanding of the underlying science.
Early discoveries
The discovery of fire was essential for shaping man’s interest in controlling
chemical change. It was soon found that mixing fire with food changed the
texture and taste of the food, and that mixing fire with mud produced hard
substances capable of holding food. This was the origin of ceramics,
developed during the Stone Age, prior to 8000 BC.
4000 BC marked the important discovery of metal (gold and copper).
By 2000 BC, man had heated copper and tin ores together and produced
bronze, hence the Bronze Age. Such an alloy was strong and available
enough to be used in weapons and as armour.
The Iron Age originated around 1500 BC after high temperatures were used
to extract iron from its ore. The metal would combine with carbon during the
process, which strengthened it and produced steel, a malleable and strong
alloy.
However by 900 BC the Egyptians were already experimenting with other
forms of chemistry, namely the preservation of human bodies with pigments
and natural juices.
Greek khemeia
The art of khemeia was developed by the Greeks over a period of 1000 years
between 700 BC and 300 AD. They were concerned with a philosophical
science, and whether, as Thales (640-546 BC) speculated, a substance could
be transformed into another, which had no resemblance to the previous
substance. This lead many philosophers of the time to conclude that
everything in the universe comprised essential elements - fire, water, air and
earth – a theory which was to be accepted for many centuries. Aristotle
(384-322 BC) proposed the Fifth Element ‘Quinta Essentia’, the origin of
‘quintessence’, describing something in its purest form.
The second main problem, which the Greek khemeia philosophers tried to
rationalize, was the question of how many divisions could be made of a solid,
and whether it was an infinite number. Leucippus and Democritus (c. 440
BC) suggested that there would be a size at which no more subdivisions were
possible. This was named ‘atomos’, meaning ‘indivisible’, and marked the
beginning of practicing alchemy.
Egyptian khemeia
Early devotees to practicing alchemy were the Greek-Egyptians. BolosDemocritus (c. 200 BC) pioneered the field of transmutation of lead and iron
into gold.
This became the ancient pseudo-science of alchemy, fuelled by the desire to
obtain a single cure for all diseases and prolong life indefinitely. Neither of
these was ever achieved, but an interest in transmutation of the elements has
remained through to the twentieth century, with the exception of the Roman
era, when khemeia had almost faded into obscurity - the emperors believed
that the ability to convert lead or iron into gold would destroy the economy of
the great Empire.
Arabic al-kimiya
Khemeia, or ‘al-kimiya’ in Arabic, was developed with novel ideas and much
enthusiasm in Arab countries.
Jabir ibn-Hayyan (c. 719-813 AD) soon became the most influential
alchemist of the Arabic world. His work included descriptions of ammonium
chloride, acetic acid and nitric acid, as well as furthering the field of classic
alchemy.
Al-Razi (c. 850-925 AD) was credited with the application of plaster of Paris
to holding broken bones in place, thus promoting the use of chemistry in
medicine.
European alchemy
European alchemy enjoyed many significant advances, which built on the
ideas of Arabic alchemists. Amongst Roger Bacon’s (1214-1292) work was
his suggestion that the development of science would be in the direction of
furthering mathematical techniques. This was largely overlooked at the time,
but would later be of critical importance over the next few centuries.
During this period, alchemy in Europe was branching into two distinct lines –
the more philosophical and mystical area and revival of interest in
transmutation, as practiced by many Spanish chemists of the time, and a
more theory based science, which lead to the discovery of many new
compounds, as practiced by several important German and English chemists
of that era.
17th century
Towards the end of the 17th century, classic alchemy had been all but
replaced with chemistry. The transition period in the 1600s saw an
increased interest in two main areas – the chemistry of gases, and the
behaviour of falling bodies.
This culminated in Robert Boyle’s book ‘The Skeptical Chymist’ (1661), in
which he showed that old teachings should not be blindly accepted, and
whose work included describing how gases are atoms with lots of empty
space between them, accounting for their compressibility, and Isaac Newton’s
book ‘Principia Mathmematica’ (1687), which introduced three laws of motion
and explained his theory of gravitiation, inspired by Galileo Galilei (15641642).
18th century
The 1700s was the age for new discoveries. Benjamin Franklin (1706-1790)
introduced the idea of expressing electric charge as a result of gained or lost
‘electricity’, later defined as the electron. This was inspired by Charles
Francois de Cisternay du Fay (1698-1739), who proposed ‘positive’ and
‘negative’ charge. Alessandro Volta (1745-1827) then made the first electric
battery and electric current, which became the origin of electrochemistry, and
suggested that electricity governed chemical reactions in some way.
The mid 1700s also saw the discovery of many new metals, including cobalt
in 1730 by George Brandt (1694-1768) and nickel in 1751 by Axel Fredric
Cronstedt (1722-1765), which shaped a new interest in what is now known as
the transition metals.
A further breakthrough in chemistry was the discovery in the 1770s of
nitrogen, hydrogen and oxygen, by Daniel Rutherford (1749-1819), Henry
Cavendish (1731-1810) and Joseph Priestly (1733-1806) respectively. This
was fundamental to biological chemistry. In addition, Cavendish’s most
significant experiment was burning hydrogen to form water vapour. Thus
since water was now shown to be a combination of two gases, the Greek
theory of the Elements had finally been disproved after an astonishing 2400
years!
Perhaps the most influential chemist of the century was Antoine Laurent
Lavoisier (1743-1794), who theorized about many subjects, most notably
recognizing the need for accurate and systematic measurements in chemistry,
the discovery that diamond was a carbon analogue, and of course defining
the concept of the conservation of mass. Later in 1789 he devised a list of
the 33 known elements. Lavoisier had incorrectly included heat and light, and
a further 8 were later found to be compounds, however he had inspired a
great many chemists to organize their findings, a quality which would later
lead to the classification of elements into periods and groups to form the
periodic table.
19th century
The 1800s produced order and a vital understanding of proportions and
standards in chemistry. The most significant of these was the idea of the
periodic table, the universal classification method of the elements. Dmitri
Ivanovich Mendeleev (1837-1907) generally has the credit for this, following
the work of many previous European chemists – Döbereiner (1780-1849),
Kekule von Stradonitz (1829-1886), Cannizzaro (1826-1910), Newlands
(1837-1898) and Meyer (1830-1895).
By the end of the century much work had been put into developing the
observation that compounds contained definite proportions of the elements of
which they were composed. This led to the ‘Law of definite Proportion’ and
later the ‘Law of Multiple Proportions’ by Joseph Louis Proust (1754-1826)
and John Dalton (1766-1844) respectively. This was of great mathematical
significance in the world of chemistry.
The late 1800s also marked the development by John Dalton of Avagadro’s
Hypothesis, the idea that balanced equations were necessary to produce a
certain amount of products from a certain amount of reactants.
Another important development of the century was in the field of
electrochemistry, particularly by Michael Faraday (1791-1867), who defined
electrolysis, electrolyte, electrode, anode, cathode, anion and cation, and who
identified the concept of an electron, and who independently proposed the
first and second Laws of Electrolysis. This paved the way for future
electrochemists.
20th century
The applications of electrochemistry were described in the early 1900s by
Joseph Thompson (1856-1940) and Robert Millikan (1868-1953), who,
amongst other things, noted that charged particles were not only deflected by
magnets, but also by an electric field. This lead to the discovery of the
electron in 1891, which was built on by Philipp Lenard (1862-1947) when he
proposed the Photoelectric Effect, the idea that electrons could be emitted
from a metal.
But perhaps the most fundamental discovery of the 20th century, the
culmination of centuries worth of experimentation and theory, was that of
the nuclear atom. Developing Marie Curie’s work on radioactivity,
Rutherford concluded that an atom comprised a dense nucleus surrounded
by empty space, in which electrons were found. In 1920 Ernest Rutherford
(1871-1937) identified and named the proton as a unit of positive charge, and
the mass of a hydrogen atom. In 1932 James Chadwick suggested the
concept of a neutron, a particle of equal mass to the proton, but with no
charge.
The idea of a nuclear atom implied that during a chemical reaction, only the
outer electrons would be affected. This led to the valence theory and was the
origin of our understanding of chemical bonds. In 1913 Henry Moseley
(1887-1915) identified the trend of decreasing wavelengths of emitted x-rays
with increasing atomic weight of the element concerned, as a direct result of
the magnitude of the positive charge in the nucleus. This was already found
to be reflected in the order of the periodic table as devised by Mendeleev in
the previous century.
Quotations
A very volatile and saline piercing liquor being dropped upon filings
of steel, the mixture grew hot. And there was emitted, out of the vial
that the steel was contained in, very fetid steams. These would kindle
at the flame of a candle and continue to burn a good while. A good name
for this would be inflammable air.2
From the Works of the Honourable Robert Boyle, Esq., Epitomiz'd,
(London, 1699-1700); quoted in J.R.Partington, A Short History of
Chemistry (New York: Macmillan, 1937).
Once there lived and existed a great learned man with a beard almost as
long as God's. And one day the people came to this man and said 'Go to
the Lord, and tell him of our misery.' 'I will go,' said the man. So he
caught a great bubble, and sat down on top of it, and flew up and up
until he pierced the heaven above us. And there he saw God and told him
of our misery and God pardoned our sins and lightened our burdens. Then
the great bearded man came down from the heavens and the people were
happy. And for this, the authorities and the tsar made this man a very
great scientist. (16)
16. D.Q. Posin, Mendeleev, The Story of a Great Chemist, Whittlesey
House, New York, 1948.