Gravity Chapter
3: The History of Atomic Theory
Greek Philosophers
From about 600 BC Greek philosophers were speculating
about the nature of the physical world and of matter itself.
Thales at this time suggested that all matter originated from water
(and that the earth was a flat disk floating in a sea of water).
Anaxagoras, who died in 428 BC suggested that all matter
consisted of infinite numbers of infinitely small particles
he called ‘seeds’ and that all bodies are simply aggregations
of these particles.
The main problem for this idea was that while the characteristics
of solid matter could be explained by it consisting of
particles all closely packed together like a pile of oranges,
it was difficult to extend this concept to explain the
fluidity of liquids and the even greater fluidity of air. Empedocles
at this time had shown that air is a substance, i.e. matter, which
can occupy space and exclude water and it clearly could not consist
of closely packed, solid particles. Air therefore had to be considered
as consisting of solid particles separated by space, but how could
these solid particles remain suspended in space without falling to
earth under the influence of gravity?
Leucippus, who has been credited with founding the atomic
theory of matter, developed Anaxagoras’ ideas. However
his writings on the subject did not survive like those
of his pupil Democritus, who about 400 BC addressed this
problem by suggesting that ‘matter consisted of
minute hard particles moving as separate units in empty space’.
But numerous questions remained, such as how these solid
particles, even if moving, could remain suspended in empty
space without falling and, as Aristotle (384-322 BC) subsequently
asked; how did these particles originally attain their
velocity?
Aristotle also rejected the concept of an ‘empty space’
or a vacuum, believing that a vacuum could not exist, and
also promoted the idea that the world was composed of just
four elements, earth, air, fire and water.
Democritus’ atomic theory lost favour amongst the Greeks
and the ‘four elements’ concept was generally accepted
and continued to be for the next 2000 years.
Dark Ages
Whilst during the time of the Roman Empire and its domination
of Europe philosophers still discussed and deliberated
on these issues however after the sacking of Rome, a new
power began to influence philosophical deliberation, the Church of
Rome.
The Christian religion, founded upon the martyrdom of Christ
and the simplicity and humanity of his teachings spread
rapidly amongst the common people of Eastern and Western
Europe aided by the zeal, the enthusiasm and the courage of the early
adherents, and later with the dispatch of missionaries from Rome.
The local rulers, the Kings, Princes, Dukes, Barons, etc.
ultimately had to recognise the Church as a political reality
that had to be accommodated. The Roman Emperor Constantine
converted to Christianity and, in the year 313, effectively
appointed it as the religion of the state.
This example was followed progressively by virtually all
the secular rulers of the lands that comprised the former
Roman Empire including Eastern, Western and Northern Europe
and the political influence of the Church of Rome grew
until effectively all these states were obliged to show
a degree of subservience to it and effectively pay taxes directly
to the Popes.
An example of the power exerted by Rome is the case of
the English King John who annoyed the then Pope (Innocent
III) in 1207 and as a result was forced to surrender the
kingdom of England to him and receiving it back in 1213
as a vassal.
By this means and from other gifts, fees and levies the
church accumulated enormous wealth and acquired huge estates.
Ultimately of course such vast wealth and power led to
corruption. The rulers of the Church of Rome, the Popes,
blatantly ignored their solemn oaths of celibacy, lived
openly with their concubines, fathering children, and in
one case appointing their bastard son as successor. They
died of syphilis, murdered, or themselves were murdered
by, their rivals.
The Bible was in Latin and apart from nobles and churchmen
not only could few people read, they of course could not
understand spoken Latin, perhaps with the exception of
a few liturgical phrases.
The local priest thus held the key to the laws that governed
peasant society and could use this or abuse this as he
pleased. An example of the powers of minor church functionaries
is the case of the English monk, Gervase of Tilbury, who
around the year 1200 tried to seduce a girl in a vineyard
near Rheims, in France. She rejected him and he subsequently
denounced her, whereupon she was arrested and tried for
heresy and was then burnt at the stake.
The papal decree of 1253 issued by Pope Gregory to set
up the Inquisition was a cynical example of the actions
of men that were appointed as the “Vicars of Christ” vowing
to uphold Christianity and Christian principles. This decree,
which effectively sanctioned imprisonment, torture and
execution of anyone who in any way opposed the authority
of the church, was a final and unequivocal demonstration
that the church was more interested in maintaining its
political power, influence and wealth than with maintaining
the Christian principles on which it was based. It was
also evidence of serious opposition to the rule of Rome
at this time and whatever the truth behind the legends of Robin Hood
(and there must be some) these were also an indication that the Church,
as an institution, was generally reviled by the common man, who was
quite aware of the abuse of power and the ingrained corruption.
With respect to the natural (observed) environment the
Roman Catholic Church accepted, and enforced acceptance
of, the Ptolemaic concept of the Earth being the centre
of the universe with the sun and the planets revolving
around it and Aristotle’s idea that matter was divided
into just four elements, earth, air, fire and water. These
concepts of course suited the creationist doctrine as set
out in the Bible and the ferocity with which the church
asserted and defended its authority thus also was extended
to these concepts and any who disagreed with it could be,
and were, denounced and branded as heretics.
The most famous of these included Galileo and Giordano
Bruno (who was burnt at the stake for his ‘heresy’), but
of course these were eminent men with good connections
and there were many thousands of ‘heretics’ of lesser worth
condemned and executed for differing from these and other
aspects of the creationist creed. These victims included,
it has been estimated, millions of so called ‘witches’,
who were mainly simple herbalist healers, and who were
in many cases denounced by priests and churchmen jealous
of their influence among the common people.
However the momentum of freedom of thought could not be
controlled by a fragmented, morally deficient and corrupt
church, and the dominance of the Roman Catholic Church
progressively declined. A significant date was the total
rejection of its ecclesiastical authority by Henry the
Eighth of England, the withdrawal of all payments to it
in 1543, and his establishment of the Church of England.
(It would of course be impossible even for an autocratic
king such as Henry to do this without public support for
this course of action.)
Renaissance
With the work of Copernicus, Galileo and Kepler,
the Ptolemaic notion of the Sun orbiting the Earth was
proven to be the reverse and this knowledge gradually filtered down
through society.
When Torricelli in 1643 invented the barometer and in doing
so, it was said, created a vacuum, one of Aristotle’s basic
beliefs was seen to be invalid.
The belief that a vacuum could exist led to a re-evaluation
of his four elements concept and of the alternative atomic
theory of matter, as propounded by Democritus.
Soon after, in 1647, Pierre Gassendi wrote that ‘atoms
(are) similar in substance, although different in size
and form, (and) move in all directions through empty space
and (are) devoid of all qualities except absolute rigidity’.
In 1662 Robert Boyle proposed that ‘at constant
temperature, the volume of a given mass of gas is inversely proportional
to the pressure upon the gas’. (Boyles Law). In other words
that the volume of a gas is dependant on the pressure to
which it is subjected.
Later Bernoulli suggested in a 1738 publication that ‘the
pressure of a gas on the walls of a vessel is the result
of the innumerable collisions of its molecules with the
walls’ and the fluctuations in pressure were explained
by the suggestion that ‘heat applied to a gas
results in an increase in the velocity of the molecules and a corresponding
increase in collisions with the walls’. Bernoulli’s concept
of gas pressure within a container is shown below.
Figure 1
In the latter part of the 1700s air and water, two of Aristotle’s
four elements, were separated into their constituent gases, which gases
were identified and named, and thus the ‘four elements’ concept was
proven to be wrong.
Dalton and Atoms
In 1808 Dalton published his Atomic Theory based upon
his observations of how different elements combine to form
compounds, such as with the combination of Hydrogen and
Oxygen to form Water.
Dalton also presented in this publication his Laws of Multiple
Proportions, (i.e. ‘when two elements combine in a series
of compounds, the ratio of weights of one element combines
with the fixed weight of the second element in a ratio of small whole
numbers’).
These laws together with Gay-Lussac’s Laws of Combining
Volumes (i.e. when gases combine they do so in volumes
that are in a ratio of small whole numbers) indicated that
matter is divided into discrete, separate particles, which
laws were seen as a confirmation of the atomic hypothesis.2
Dalton had assumed that one atom of oxygen combined with
one of hydrogen to form a water molecule and experiments
had also shown that a volume of pure hydrogen had a mass
that was one sixteenth of that of the same volume of oxygen,
and a problem for the emergent kinetic-atomic theory of
gases was, within the constraints of the theory at this time; to
explain how both gases, consisting of atoms of widely different masses,
exert the same pressure on the walls of their separate containers.
In other words how did lighter hydrogen atoms produce the same pressure
as heavier oxygen atoms?
This was solved by suggesting that lighter atoms, in producing
the same pressure in similar circumstances as heavier ones,
can be assumed to achieve this by having greater kinetic
velocities and therefore colliding more frequently with
each other and with the walls of any container.
Thus it was calculated that, at atmospheric pressure, hydrogen
atoms have an average velocity of about 1800 metres per
second while oxygen and nitrogen atoms, whose relative
masses were about 16 and 14 times that of hydrogen, have
velocities in the region of 450-500 m/s.
However a new problem soon arose, with the examination
of the characteristics of elemental gases when combining
with other gases to form compounds.
For example, one volume of hydrogen gas combines with one
of chlorine gas to form two volumes of the gaseous compound
hydrogen chloride. The original assumption was that one
atom of hydrogen joined or bonded together with one atom
of chlorine to form a single molecule of hydrogen chloride
as represented in Figure 2A below.
Figure 2
The problem for the assumption that equal volumes contain
equal numbers of atoms is that it raises the question as
to how a single molecule of hydrogen chloride can produce
the same pressure in the same volume originally occupied
by the atoms of the two separate gases, as depicted below.
To do this it would have to increase its kinetic motion,
or velocity, significantly to nearly double that of the
original chlorine atom, and of course it could not be explained
as to where the necessary extra ‘kinetic’ energy would
come from to do this.
Avogadro
In 1811 Avogadro proposed a solution to this problem by
suggesting that equal volumes of different gases contain
equal numbers of atoms, and that certain elemental gases
consist ultimately of di-atomic ‘molecules’. In other words, in these
particular gases (which included hydrogen, oxygen, nitrogen and chlorine),
two atoms were bonded together to form an elemental ‘molecule’.
[Other (inert) gases such as helium, neon, argon, krypton,
xenon and radon were later suggested to be monatomic, still
other elements including phosphorus, arsenic, antimony,
sulphur, and selenium were said to be polyatomic. (Up to 6 or 8 atoms
bonded together)]
This idea, as represented above in part B, would appear
to solve the problem of pressure but it again raised serious
questions, in the context of the theory where atoms were
perfectly elastic, rigid balls that were in constant motion
and colliding with and rebounding from each other; why
and how did atoms of some gases join or bond together strongly
in pairs, while other atoms of other gases did not?
Continued >
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