Matter, Light and Energy
The quest to discover the basic fundamental
substance that is matter:
- ancient Jews:
- Genesis creation story:
- first things created were earth, heavens, light & water
- ancient Greeks & Romans:
- were fascinated by the concept of matter & how it was formed &
- the 4 elements:
- Empedocles (b. 492BC), noting that when wood burnt, it gave off
fire, smoke ( a form of air), & ash (a kind of earth), devised a
theory that all matter could be broken down into the essential 4
components of earth, air, fire & water. This was accepted by
the western world for the next 2000 yrs, although competed with the
"atomists" theory of Leucippus (450BC), which although
present, was over-powered by the 4 element view of matter.
- Zeno (470-460BC) "all matter was like a huge jelly that filled
- the "atomists":
- the term 'atom' is derived from the Greek atomos meaning
'that which cannot be divided or cut';
- Leucippus (450BC): "all matter was broken into minute particles
with space between them"
- Lucretius (c50BC): added to Leucippus' theory the idea that the minute
particles were indestructible & eternal
- ancient Indians:
- in 500AD, had developed a complex theory of atomism which included the
notion of atomic size & that atoms were 10-9 cm in
size which is remarkably close to modern measurements!!
- medieval alchemists:
- medieval alchemists believed that it would be possible to transmute
common base metals into noble metals such as gold & silver,
unfortunately for them they failed
- modern chemistry:
- by the time of Robert Boyle in 2nd half of the 17thC, when the
foundations of modern chemistry were being laid, it became increasingly
established in belief that changing an element from one metal to another
- 1658: Gassendi revived the interest in atomic theory of the ancient
Greeks & discussed the possible applications of atomic theory as
well as coining the term 'molecule' for groups of atoms.
- Boyle & Newton applied atomic theory to such scientific problems
as the nature of sound & light & the principles of motion.
- work on atomic weights & combinations set the scene for Dalton to
start the development of the modern atomic theory.
concept of the modern atom as a billiard ball with kinetic energy:
- 1808: Dalton's publishes his New System of Chemical Philosophy
and established the concepts:
- that all atoms of one element are the same & atoms in one
element are different from atoms in other elements
- different atoms have different atomic weights
- all atomic weights should be measured against a base of hydrogen
- atoms join each other on a one-to-one basis although this idea was
- 1808: Gay-Lussac established that atoms combine in different ratios
- 1811: Avogadro suggested that molecules or clusters of atoms may be
the smallest units of many elements & that equal volumes contained
equal numbers of molecules (these were ignored until re-stated in 1858
- Clerk Maxwell "atoms were and always had been, in all
periodic table of elements:
- 1812: early expts in electrolysis leads to Berzelius assigned
certain atoms a positive charge (eg. sodium) and others a negative
charge (eg. chlorine) leading to an early theory of valency & the
concept that atoms combine because they attract each other electrically.
- relative atomic masses determined
- 1829: Dobereiner noticed that certain groups of 3 chemically similar
elements had values which were in approx. arithmetic progression,
forming Dobereiner's triads
- 1838: Liebig idea of acids being compounds containing hydrogen
replaceable by metals to form a "salt"
- 1839: Dumas proposed there were certain fundamental types of chemical
compound & that any element or group of elements in these types
could be replaced, equivalent for equivalent, by another element or
group of elements. This theory was successful in organic chemistry &
eventually developed the idea of homologous series.
- 1864: Newland's law of octaves - by arranging elements in
ascending order of relative atomic mass & assigning the elements a
series of ordinal numbers which he called atomic numbers, he
noticed that similar elements had atomic numbers that differed by 7 or
some multiple of seven.
- 1869: Mendeleef's law of periodicity, which essentially
restated Newland's law, was supported by the periodic relationships
noticed by Lothar Meyer in plotting atomic volumes ( relative atomic
masses / densities ) of the elements against their relative atomic
- 1895: X-rays were discovered by Rontgen forming
the starting point of modern physics as well as revolutionising
diagnostics in medicine.
- 1895: Ramsay showed that that a gas liberated from uranium had the
same spectral characteristics as helium
- 1896 radioactivity of uranium was discovered by Becquerel, then in 1898,
Curie discovered radium
- Rutherford discovered alpha & beta rays and by 1899, the
electron - the 1st sub-atomic particle - had been discovered.
- 1897: J.J.Thomson discovered that atoms were actually made of
electrons, suggesting that atoms could be divided.
- these, along with research into the photo-electric effect in 1898,
were to set the scene for Rutherford to change our perception of
matter with his vision of the atom & its structure, and for
Einstein to change our perception of space and time.
- 1903: Rutherford renames "long penetrating rays" as gamma
rays but their nature was uncertain
- 1903: Rutherford finally shows he can deflect alpha rays with both
an electric field & a magnetic field & showed that the ratio
of its charge to mass was approx. one half that for the hydrogen
- 1903: Soddy & Ramsay show that that a gas liberated from
radium had the same spectral characteristics as helium
- 1903: Lenard using a cathode ray tube shows that an atom had an
open structure & was mostly empty space
- 1904: Rutherford shows that the charge of an alpha particle is
twice that of an electron & thus its mass must be 4 x that of
hydrogen atom, therefore an alpha particle was probably an helium
atom which was expelled during the process of disintegration
- 1904: the transmutation of radioactive elements:
- Rutherford in his Bakerian lecture proposes that as the half
period of radium is of the order of a thousand years, any radium
that had been there 100,000yrs ago would have vanished, thus
radium must be renewed by some very long-lived radioactive
substance which he thought would be uranium. His theory was
later supported when he showed that uranium ores from various
parts of the world all had the same proportion of radium to
uranium. He also predicted that the final breakdown element of
many of these would be lead.
- Rutherford also stated that the heat generated from
radioactivity would slow down the cooling of the earth which
would make Lord Kelvin's calculation of the age of the earth
based on its current temperature of 20-40 million years to be
- 1905: Einstein postulates his quantum theory to explain the
- he interpreted results which showed that for each metal there is a
critical wavelength above which no photo-electrons are emitted, as
meaning that radiation could be regarded as made up of small
'packets' of energy, known as photons, when a metal is irradiated by
such photons, some of the energy was used in ejecting electrons from
the metal whilst the remainder was given up to the electrons.
- the energy of a photon is dependent on the wavelength, or
frequency, of the radiation concerned according to the basic
equation of the quantum theory E = hv
- 1905: Rutherford discovers that thorium's radioactivity decays with a
half-life => "disintegration theory"
- 1908: Rutherford proves that alpha particles are helium atoms and
working with Geiger, use the scintillation method for measuring the scattering
when a narrow beam of alpha rays passes through a thin sheet of
- 1909: Geiger & Marsden complete their scattering expts which
surprisingly showed that occasionally, an alpha particle travelling at
10,000 miles/sec is bounced back, which suggested to Rutherford that
atoms may have a small dense nucleus from which the particles bounced if
- 1911: Rutherford's atom with a nucleus surrounded by
electricity - his view of the atom as having a nucleus containing alpha
particles, so well protected from, so inaccessible to, ordinary physical
& chemical action, that it cannot be broken up by ordinary chemical
or physical forces. The nucleus had a charge of magnitude Ne, where e =
unit electronic charge & N is a whole number, and was surrounded by
a sphere of electricity of the opposite kind. He could not say if the
nucleus was positive or negative as either would account for the scatter
paths of alpha rays.
- 1912: von Laue proves the wave nature of X-rays by passing them
through a crystal & Moseley showed that different elements produce
different X-ray spectra & that the square root of the characteristic
frequency increased by a constant amount as one passed from one element
to the next when the elements were arranged in order of atomic weight,
but that it was the atomic number itself that correlated, not the
weight. To Moseley, this proved that there is a fundamental quantity in
an atom which increases by regular steps as we pass from one element to
the next. This quantity can only be the charge on the central positive
nucleus. Thus, the N in Rutherfords Ne nuclear charge was equivalent
to the atomic number. He then predicted any missing elements could
be identified using this & indeed 4 gaps were found & later
elements were discovered to fill these gaps.
- 1912: Wilson devises his cloud chamber for photographing tracks
of alpha particles
- 1913: after working with Rutherford, Geiger invents the Geiger
- 1913: discovery of isotopes - elements existing having
identical chemical properties but different masses - suggested that
nuclei have the same charge but different masses
- 1914: Rutherford and Andrade using X-ray crystal analysis methods,
showed that gamma rays were of the same nature as X-rays but of shorter
- Bohr's atom based on quantum theory:
- the problem of the hydrogen spectrum:
- whilst solid objects when heated give out visible light of all
frequencies due to closely packed atoms interfering with each other,
a gas at low pressure through which an electric discharge is passed,
gives out sharp spectral lines which represent certain well-defined
- as hydrogen is the simplest atom, its spectra was studied and
Balmer showed that its frequencies formed a series - the Balmer
series - that obeyed a very simple law being proportional to (1/22
- 1/n2) & later Ryder showed that to get the wave
numbers from these for use in wave equations, a multiplier must be
used - the Ryder constant
- the problem was that if a moving charged particle produced this
light, it should do so at a single frequency & produce a
monochromatic light, and if it lost energy in giving out the light,
its orbit should gradually diminish producing a continuous range of
frequencies, but here was hydrogen with a single electron producing
a number of discrete frequencies!
- 1913: Bohr solves the problem of the hydrogen spectrum using quantum
theory by postulating that:
- electrons move around the nucleus & those moving in an atomic
orbit did not radiate
- the laws of electromagnetism that explained large-scale physics
did not apply to atoms which had their own laws
- of all the infinite variety of orbits that were permitted by
classical laws, only certain widely separated ones were actually
possible, these being determined by a special quantum condition
- if all electrons were circulating in these orbits then the atom
was in a "stationary state" & to each stationary state
would belong a certain energy, which could be calculated by Bohr's
- the atom sent out radiation only when it passed from one
stationary state to another (eg. when an electron moved from one
legal quantum orbit to another), the frequency of the radiation was
given by the difference in energy between the two states divided by
h (Planck's constant)
- it is the electrons that are responsible for the chemical
properties of an element, leading in 1916 to the study of ionic
& covalent bonds, electronegativity of elements
- Rutherford shows that that particles which alphas knocked out of
bombarded nitrogen were hydrogen nuclei to which he gave a special name,
proton. This presumably led to Bronsted & Lowry in 1923
formulating their concept of acids & bases as being proton
donors & proton acceptors respectively.
- 1920: Rutherford in his 2nd Bakerian lecture, predicts the existence
of heavy hydrogen (deuterium - discovered in 1931) and also light
helium, but most remarkable of all was his anticipation of the existence
of a particle with zero nuclear charge, the neutron which was
discovered in 1932 by Chadwick
- 1925: Uhlenbeck & Goudsmit postulate electron spin to
account for the splitting of many single spectral lines into double
lines when examined under a spectroscope of high resolving power.
- Pauli exclusion principle - if two electrons occupy the same
orbital, they must have different spins thus no orbital can contain more
than 2 electrons.
- 1930: Ernest Lawrence invents the cyclotron, a machine to
accelerate a particle to energy of tens of MeV.
- quantum mechanics:
- in the 1920's, Heisenberg, Dirac & Schrodinger developed a new
picture of reality called quantum mechanics
- no longer did tiny particles have a definite position & speed but
introduced the Uncertainty Principle which stated that the more
is known about the position of a particle, the less can be known about
its speed & vice versa
- these became the foundation of modern developments in chemistry,
molecular biology & electronics.
- 1924 de Broglie suggested that moving electrons had waves of
definite wavelength which was demonstrated in 1927 and their
wavelength = h/mv where h is Planck's constant, m is mass of electron
& v is the velocity of the electron & if this is written as
momentum x wavelength = h & thus relates the particle-like aspect of
an electron ie. its momentum, to the wave-like aspect, ie. wavelength.
- 1927, Schrodinger postulated based on his intuition without proof,
that the wave pattern of an electron could be expressed as an
equation relating a wave function, the total energy & potential
energy of the system, mass of the electron, Planck's constant & the
coordinates of the system.
- 1927, Heisenberg put forward the Uncertainty Principle as a
long wavelength can be measured with greater fractional accuracy than a
short one, thus according to de Broglie's equation, a particle with
small momentum has a correspondingly large wavelength which can be
measured with some accuracy but at the expense of a relatively
inaccurate determination of the small momentum.
- artificial transmutation of elements:
- 1934: Joliot-Curies found that by bombarding light elements such as
boron, magnesium & aluminium with alpha particles, radioactive
isotopes could be produced, some of which gave out positrons in the
course of their rather rapid decay, a new feature.
- Fermi showed a special effectiveness of neutron particles in
penetrating heavy elements with large nuclear charges which otherwise
repel alphas so strongly that they cannot get near enough to cause any
disintegration. He was able to produce, out of 63 elements investigated,
37 new elements showing radioactive properties, among these were new
elements produced from thorium & uranium, which were heavier than
any natural elements & they were radioactive in a different way by
giving out beta particles (electrons) instead of alpha particles. He
also showed that neutrons that had been slowed down by repeatedly
hitting protons, were more effective in producing atomic transmutations
than fast neutrons.
- 1936: Rutherford predicts the possibility of producing energy on an
industrial scale from nuclear transmutation.
- 1937: Rutherford dies.
- 1938: in response to Mussolini adopting the Nazi code, Fermi
leaves Italy to go to US
- Einstein predicts the possibility of releasing enormous amounts of
energy by splitting the atom & thus nuclear explosions.
- the splitting of the atom:
- 1939: Hahn & Strassmann in Germany stumble upon the process of
fission when they bombarded uranium & produced barium and krypton
thus splitting the atom "nuclear fission" with the
final mass being lower than the initial & thus the difference in
mass was the energy released. Scientists now realised the potential energy source they had discovered.
Joliot-Curies now suggested the possibility of a chain reaction using
the expelled neutrons which are faster than the ones used to create the
reaction, to release an enormous amount of energy. The smallest amount
of material needed to sustain a chain reaction is called the critical
- U235 + neutron => U236 => La148
+ Br85 + 3neutrons + 0.20 amu which becomes kinetic
- 1940: Seaborg & McMillan discover plutonium;
- 2 December 1942: Fermi et al at Chicago demonstrated that the chain
reaction created by 'splitting the atom' could be contained & was
thus self-sustaining. This was the vital experiment that ensured that
all the previous work would eventually lead to the atomic bomb.
- it took 2.5yrs, the labour of 500,000 people & $1.4b before the
Manhattan Project as it was called, successfully converted Fermi's expt
into a bomb. Much of the expense entailed taking quantities of raw
uranium & producing adequate amounts of the rare but highly
fissionable material U-235.
- 16 July 1945: at Alamogordo in New Mexico, the 1st atom bomb was successfully
- 6 August 1945, an atom bomb using uranium was dropped on Hiroshima,
and 3 days later an atom bomb using plutonium was dropped on Nagasaki,
the resulting explosions killing 120,000 people but resulted in an end
to the war with Japan.
- If the chain reaction is uncontrolled, an explosion will result - an
atomic bomb, however, if suitable materials are introduced to absorb and
slow down the neutrons, a controlled reaction can be established with
energy produced at a predicted rate - this is the principle of the nuclear
reactor power station, the typical components of which are:
- fissionable fuel (uranium or plutonium)
- the moderator (graphite or D2O to slow down the fission-producing
- the control rods (usually Cd strips, whose insertion captures
neutrons & slows the fission rate)
- a coolant (water, air, hydrogen, or liquid metal such as sodium)
- nuclear energy may also be produced by nuclear fusion which is
the fusion of small nuclei into larger nuclei with loss of total mass in
the system & thus release of energy. Nuclear fusion is the process
that occurs on the sun as it converts hydrogen atoms to helium, but as
this requires temperatures found in stars whilst the reactants must be
confined within walls which wont melt (perhaps a magnetic containment
field), it has yet to be made possible by man. The initial steps would
be to heat the hydrogen atoms sufficiently to strip them of electrons
& thus produce a "fourth state of matter" - a fully
ionised gas or plasma.
- the hydrogen bomb is large scale fusion of deuterium using a
fission bomb in the centre to produce the high temperatures required for
- the structure of crystals and polyatomic
- 1939: Sidgwick-Powell rule - the approximately spherical charge clouds
within a particular electronic shell will stay as far away from each
other as possible
- 1951: Bethe & van Vleck introduce crystal or ligand field theory,
initially to ionic crystals, but Orgel developed its more general
- 1957: Gillespie & Nyholm fully develop use of the Sidgwick-Powell
rule to predict molecular shapes
- more sub-atomic particles:
- 3 technologies combined in the early 1960's to enable the discovery of
many more sub-atomic particles:
- more powerful particle accelerators
- the bubble chamber
- computers to analyse data from the bubble chamber
- matter consists of fundamental matter particles quarks &
leptons (eg. electron, muon, tauon & neutrinos) with 6 flavours
- all subatomic particles have spin:
- fermions (1/2 spin) eg. quarks, leptons
- bosons (0, 1 or 2 spin): eg. photons, gluon
- matter particles acted upon only by strong nuclear force are
- baryons (3 quarks, fermion-type): proton, neutron
- mesons (1 quark, 1 antiquark, boson-type, unstable): pion
- 4 known fundamental forces, each mediated by a fundamental
particle (quantum, known as a carrier particle):
||7 x 10-3
||W+, W-, Z
||6 x 10-39
- not particles but strings:
- an extension of quantum physics using strings (one-dimensional
extended objects that vibrate) to represent the "particles"
form the super-string theories of the mid-1980's
- see the origin of the Universe
- 1928: a young physicist named Paul Dirac solved the problem of
combining quantum theory with special relativity by creating a strange
mathematical equation but this also in some way, predicted the existence
of an antiworld identical to ours but made out of antimatter.
Dirac speculated on the existence of a completely new Universe made out
- 1930: the invention of the cyclotron - when a particle is accelerated
to the speed of light then is rapidly stopped, it gives off energy in
the form of incredible heat which in turn creates a particle and an
anti-particle, these if they collide, will annihilate each other and
give off energy in the form of light.
- 1932: Carl Anderson discovers the anti-electron which he called a
positron which was confirmed by Blackett in 1933.
- 1954: Lawrence invents the Bevatron, a particle accelerator optimised
to produce anti-protons by colliding two protons at 6.2GeV. The anti-proton
was discovered in 1955 by Segre & his group.
- 1960: the anti-neutron is discovered.
- 1965: an anti-deuteron (a nucleus of antimatter made out of an
anti-proton & anti-neutron) was created at Cern.
- 1980's: NASA consider antimatter as a propulsion as it is the perfect
fuel with all its matter converted into energy - 1kg converted to energy
equates to 25,000,000,000 kWh energy - 1g would supply a medium sized
town for 1 day. But antimatter proved to be very difficult to create
& requires enormous amounts of energy!
- 1990's: the PET scan for scanning brains:
- When electron and positron meet, they annihilate, turning into
energy which, at high energies, can rematerialise as new particles
and antiparticles. This is what happens at machines such as the
Large Electron Positron (LEP) collider at CERN.
- At low energies, however, the electron-positron annihilations can
be put to different uses, for example to reveal the workings of the
brain in the technique called Positron Emission Tomography (PET).
- In PET, the positrons come from the decay of radioactive nuclei
incorporated in a special fluid injected into the patient. The
positrons then annihilate with electrons in nearby atoms. As the
electron and positron are almost at rest when they annihilate, there
is not enough annihilation energy to make even the lightest particle
and antiparticle (the electron and the positron), so the energy
emerges as two gamma-rays which shoot off in opposite directions to
- 1995: Cern's unique Low Energy Antiproton Ring (LEAR) that slows down
anti-protons creates 9 high energy anti-hydrogen atoms. CERN can
produce 50 millions antiprotons in each cycle (about once a minute),
that allows them to make a few hundred antihydrogen atoms (ie. a
billionth of a gram per year). Cern thus decided to create the 1st
"self-contained antiproton factory" - the Antiproton
Decelerator (AD) which produces the low energy antiprotons needed to
- 2002: Cern create 50,000 low energy anti-hydrogen atoms.