What are SPLATs? They are explained here.
The principles of atoms
- At a simple level, matter can be thought of as atoms that are
indivisible, so long as we know that this is a very simple first
approximation to the whole truth.
- Atoms cannot be created or destroyed in theory, but in
practice, many atoms can be changed permanently, in small numbers, by
interactions with their nuclei.
- Atoms have characteristics which can be measured, such as
having a measurable size and they have a constant mass that can be
measured with a mass spectrometer.
- Atoms may not be seen, but the positions of individual
atoms may be located in a variety of ways, increasing our confidence
that atoms are real objects.
- Some time before 50 BC, the poet Lucretius had suggested in
Rome that matter was made of atoms, though these atoms were little like
the atoms we know today.
- In 1808, John Dalton published his theory that all matter
was made of atoms, bringing a revolution to chemistry, even though
others had suggested atoms earlier.
- John Dalton's first principle in his atomic theory was that
the chemical elements are atoms which do not change, even when they
take part in a chemical change.
- John Dalton's second principle, given that the elements are
made of unchangeable atoms was that all of the atoms of a particular
element are identical.
- John Dalton's third principle in his atomic theory , given
that atoms exist, was that chemical compounds form when atoms combine in
simple numerical ratios.
- Under some circumstances, the indivisible atoms may be
considered in terms of their components to any degree of complexity,
depending on the detail we need.
- For most parts of chemistry it is sufficient to consider
atoms to be made up of protons and neutrons in the nucleus, and shells
of electrons orbiting around it.
- An atom's emission spectrum reflects quantisation in a way
that we can observe in our less confusing real world where most quantum
effects are hidden from view.
- Sir William Crookes used spectral analysis to discover the
element thallium compounds as an impurity in selenium ores, though he
did not isolate the element.
- Jean Foucault, the inventor of the pendulum, probably also
first discovered the way the emission and absorption effects are linked,
but the did not publish it.
- The absorption spectrums of atoms may also be taken as
evidence that atoms are real objects, rather than theoretical constructs
dreamed up by theoreticians.
- A laser mass spectrometer can identify tiny samples by
molecular weight, after the molecules are fragmented and accelerated so
their momentum can be measured.
- The observation of Brownian motion provides direct evidence
for the existence of atoms as small particles in a colloid or a
suspension are seen to be buffeted.
- Diffusion happens when atoms or molecules move randomly. It
offers further evidence for matter existing as atoms and molecules
since light gases diffuse faster.
- A mass spectrometer 'weighs' atoms, and the fact that it
gives constant results, allowing for isotopes, offers further evidence
that matter is made up of atoms.
- In 1799, Proust showed that copper carbonate from several sources had the same amounts of copper, carbon and oxygen, leading to the Law of Constant Proportions.
The principles of the structure of atoms
- Similar atoms have similar chemical properties which depend
mainly on the number of electrons in the outside shell, but also on the
size of the nucleus.
- Atoms are made of fundamental particles: in simple terms,
the nucleus is made up of protons and neutrons, and the electrons are
found around an atom in shells.
- An ion is an atom or group of atoms which is charged
because it has a net deficit or excess of electrons. Ions of an element
nearly always have the same charge.
- The nucleus of an atom may be thought of as being made of
protons and neutrons, although at a certain point in the study of
physics, this is seen as too simple.
- Atoms have electron shells which can be detected, giving
them some reality: much about atoms relates to quantum physics, and is
somewhat surreal, as we see it.
- The shell structure of the electrons in any given atom is
reflected in the successive ionization energy values for that atom,
measured as atoms are removed.
- Electrons are arranged in a shell structure that influences
the chemical properties of the elements, most of the influence coming
from the outermost shell.
- Chemical elements have atoms that are essentially all the
same. Elements occur as isotopes of slightly different mass. Elements
generally have several isotopes.
- Isotopes are generally considered chemically identical, but
some chemical and biochemical processes can separate them or cause one
of them to be concentrated.
- Johann Balmer took a series of measurements for 'hydrogen
lines', as observed in stellar spectra, and found a simple formula
linking the values to each other.
- Balmer's hydrogen line calculations seemed at first like
simple mysticism, but new lines could be predicted, and later they were
the key to electron shells.
- J. J. Thomson proposed his plum pudding atom model, but
soon after it was first suggested, it did not match many observations,
so a better model was needed.
- Thomson's plum pudding model assumed atoms filled all of
the space they existed in, with no spaces, a mix of protons and
electrons (neutrons were unknown).
- Geiger and Marsden found in 1909 that alpha particles fired
at metal foil mostly went through, but 1 in 20,000 bounced back or was
deflected by 90 or more.
- Rutherford described this result as surprising " . . . it
was as if you had fired a 15-inch shell at a piece of tissue-paper and
it came back and hit you."
- Based on the gold foil and alpha particles experiment,
Rutherford proposed an atom with a small massive nucleus of protons
surrounded by orbiting electrons.
- In 1911, Ernest Rutherford explained the Geiger-Marsden
experiment by invoking the nuclear atom, and inferred the nucleus from
the alpha scattering result.
- By 1911, Rutherford had taken this result, and used it to
model an atom where the atom had a diameter about 10,000 times the
diameter of the tiny nucleus.
- Ernest Rutherford's 1912 model of the atom, which had a
positive nucleus with orbiting electrons was both mechanically and
electromagnetically unstable.
- The Rutherford model of the atom did not fit observations:
in particular, circular orbits were simply not possible, but it is still
the popular view of an atom.
- The simple model of orbiting electrons around an atom
fails: a circular orbit involves acceleration, and accelerating charged
particles must emit radiation.
- In 1913, one year after Rutherford proposed an atom with a
positive nucleus and orbiting electrons, Niels Bohr showed how the model
could be rendered stable.
- In 1915, Arnold Sommerfeld developed a modified Bohr atomic
model using elliptical instead of circular orbits to explain
relativistic fine structure.
- In 1931, Harold Urey discovered deuterium using evaporation concentration techniques and spectroscopy to identify the heavier isotope of hydrogen.
About the elements
- Elements have atoms that are essentially all the same. Elements may
occur as allotropes. Example: Graphite and diamond are both allotropes
of carbon.
- Chemical elements have characteristics that can be
measured. The radius of atoms as you move to the right on a row of the
periodic table gets smaller.
- Chemical elements have a fixed density, fixed melting and
boiling points, fixed latent heats and fixed specific heats, if they are
in the same allotropic form.
- Once people could look at pure samples of oxygen,
phosphorus and so on, they were most of the way to accepting that atoms,
once mere theories, really existed.
- Elements show patterns in reactivity, and a displacement
reaction provides clear evidence of relative reactivity when two
elements are compared with each other.
- By John Dalton's time, many different chemists in western
and northern Europe were beginning to discover and prepare pure samples
of the different elements.
- Some elements can exist in one stable form or allotrope,
with varying properties. Elements with allotropes include carbon,
phosphorus, oxygen, sulfur and tin.
- A small number of elements are able to form ions with more
than one charge: examples include iron, copper and mercury. The
properties of the ions are different.
- In 1894 Lord Rayleigh and William Ramsay discovered argon
by spectroscopic analysis of the gas left over after nitrogen and oxygen
are removed from air.
- Stanislao Cannizzaro popularized the idea that molecules of
elements need not be single atoms, explaining a number of puzzles about
gases, up until then.
- William Prout's lasting fame comes from his anonymous
suggestion in 1815, that the atomic weights of the elements were all
multiples of that of hydrogen.
- In effect, William Prout argued, in what was later called
'Prout's hypothesis', that all atoms are made up of clusters of hydrogen
atoms in varying numbers.
- In 1789, Antoine Lavoisier described conservation of mass
in chemical reactions, listing 31 substances believed to be elements
(eight were compounds).
- In 1811, Bernard Courtois discovered the element iodine, while making potassium nitrate from ash derived from seaweed, as part of France's war effort.
The principles of the periodic table
- Because similar atoms have similar properties, we can arrange
the elements in a table called the periodic table, and we can see
relationships and trends in it.
- Some properties of matter show clear trends and patterns,
and the periodic table of the elements reflects many of the patterns
that may be seen in the elements.
- The atoms of the elements, ordered by relative mass show
regular patterns, which may be seen in any systematic study of the
periodic table of the elements.
- Similar elements in the periodic table are usually in the
same group: the halogens are a typical group, as are the alkali metals,
noble gases and alkali earths.
- As the periodic table developed, it became possible to find
gaps and predict new elements, which chemists could then seek to find,
somewhere in nature.
- In 1817, Johann Wolfgang Döbereiner drew attention to the
existence of triads of elements, pointing to the oxides of calcium,
strontium and barium.
- In 1828, Jöns Berzelius was able to provide a table of 28
elements which had been identified by then, but it was not enough to
allow any patterns to be seen.
- By 1829, Döbereiner noted that there were triads, groups of
three elements. Chlorine, bromine and iodine made one, lithium, sodium
and potassium made another.
- In 1865, John Alexander Reina Newlands proposed his 'law of
octaves', which became a further helpful step on the way to the first
rows of the periodic table.
- In 1871, Dmitri Mendeleev systematically examined the
periodic table and by identifying gaps, predicted the existence of
gallium, scandium, and germanium.
- Dmitri Mendeleev had a total of 63 elements to work on in
1869, enough to have a reasonable chance of detecting any periodic
tendencies in the elements.
- Dmitri Mendeleev studied atomic weight, specific gravity,
volume, valence, specific heat and other properties for each of the
elements to find trends.
- Mendeleev's ideas differed from the earlier schemes to
organize the elements because he got the order right, and because he
left room for undiscovered elements.
- In each case, Mendeleev pointed out that the atomic weight
of the middle member in the triad was close to the arithmetic mean of
the other two atomic weights.
- Norman Lockyer used a spectral analysis of light coming
from the Sun to find helium in the Sun before the element was ever
discovered here on Earth.
- Ramsay and Rayleigh found argon, and reasoned, if there was
one new element to fit into the periodic table, there should be more,
one for each row of the table.
- In 1906, Charles Barkla found each element had a
characteristic X-ray and that the penetration of these X-rays was
related to the atomic weight of the element.
- In 1914, Henry Moseley had shown that nuclear charge was
the real basis for numbering the elements, counting for more than
average nuclear mass.
- Like Mendeleev, Henry Moseley was able to find gaps in his
pattern and from these, predicted three undiscovered elements:
technetium, promethium, and rhenium.
- Moseley's three predicted elements have since been either discovered (technetium and rhenium) or made (promethium has never been found in nature).
The principles of compounds
- Compounds have a fixed composition involving small numbers of atoms
in whole number ratios which remain constant from sample to sample of
the compound.
- Atoms link up in small whole number proportions to form
molecules, although more than one combination may be possible, as in
carbon monoxide and carbon dioxide.
- When two compounds have the same atoms and different
proportions, the properties of the compounds will be quite different, as
in water and hydrogen peroxide.
- A compound is often formed of an element and a group which
remains linked during chemical reactions, even as it changes partners,
behaving almost as an element.
- The existence of chemical compounds with fixed proportions
is further evidence for the reality of atoms as the base unit of matter
as we experience it.
- In 1865, Josef Loschmidt estimated the number of molecules
in a fixed volume (1 cc, today, one millilitre) of gas, from kinetic
theory, Loschmidt's number.
- In 1873, James Clerk Maxwell estimated Loschmidt's number
as 1.9 x 10^19, equivalent to an Avogadro's number of 4.3 x 10^23, about
2/3 of the accepted value.
- In 1908, Jean Perrin studied Brownian motion in water, relating this to the size of the water molecules, getting a good estimate of the size of the molecules.
The principles of mixtures
- Mixtures are variable, and can be separated more easily than
compounds, using purely physical means such as filtration, flotation,
magnetism or distillation.
- Mixtures are more variable than compounds. The parts can be
separated more easily using purely physical methods like filtration,
flotation and distillation.
- A solution is a mixture made up of a solute (the thing
dissolved) and a solvent (the thing dissolving). A solute and solvent
cannot be separated by filtration.
- An emulsion is a mixture in which the particles are too large and discrete for it to be regarded as a solution, but which are fairly well mixed together.
Chemical properties
- The chemical and biochemical properties of molecules depend on the
shape, charge, preferred charge, actual charge and distribution of
charge over the molecule.
- Metals usually conduct electric currents and heat better
than non-metals. Most metals can be hammered into shape, and many can be
melted and poured into moulds.
- Metals are elements with a few electrons only in the
outermost shell. These electrons are only loosely held, and this is why
metals conduct electricity.
- Many materials are melted more easily by adding them to a
flux which melts at a low temperature than they do, and effectively
takes the material into solution.
- The melting points and boiling points of all materials can
be measured. For pure substances under the same conditions, these values
always remain constant.
- One common test for the purity of organic chemicals (including some drugs of addiction) is to measure their melting points, which will be lowered by impurities.
The principles of gases
- Around 1620, Jan Baptista van Helmont coined the new word 'gas',
taking it from the Flemish word for 'chaos', suggesting he had some
notion of what gases are.
- In 1661 Robert Boyle published his 'Sceptical Chymist' and
stated his law for ideal gases relating volume to pressure, and made a
number of other key points.
- In his 'Sceptical Chymist', Robert Boyle made reference to
chemical elements, acids and alkalis, and offered a corpuscular theory
of matter, all in one year.
- An ideal gas obeys the law described in the gas equation.
Real gases approximate reasonably well to Boyle's law, Charles' Law and
the combined gas law.
- The first person to propose that gases were made of
particles was Daniel Bernoulli, who realized that assuming a gas made of
particles explained its behaviour.
- The behaviour of gases may be explained by using the
kinetic molecular theory which considers the gas molecules as
independent particles, able to move freely.
- In 1848, James Joule calculated the average velocity of gas
molecules from kinetic theory. It contained the first numerical results
from the kinetic theory.
- The diffusion of gases obeys Graham's law of diffusion,
which says that the square root of the density of the gas is inversely
proportional to its velocity.
- The reactions between gases follow Gay-Lussac's law, which
states that the volume ratios of the reactants and the products will
involve small whole numbers.
- Avogadro's hypothesis proposed that equal volumes of gas
under the same conditions of temperature and pressure, contained the
same number of molecules.
- In 1772, Joseph Priestley discovered that the volume of air
decreases when an electric spark passes through it, but did not explain
the effect.
- Avogadro's constant is the number of molecules of a
compound with a mass in grams equal to the molecular weight, and as a
gas, occupies 22.4 litres at STP.
- In the 1890s, Rayleigh found that nitrogen prepared from
air had a different density from nitrogen which was prepared chemically.
The difference was argon.
- In 1798, Humphry Davy was involved in treating people with gases. During this work, he saw the effects of laughing gas (nitrous oxide), and wrote about them.
The principles of the separation of materials
- Distillation relies on differences in boiling points in two liquids.
The vapour that is driven off will be richer in one component than the
original mixture.
- One way of separating dissolved material is by steam
distillation, which applies a carefully controlled heat which does not
harm delicate molecules.
- Much of industry depends on effective ways of preparing
pure chemicals in significant amounts at a sufficiently low price and at
a low cost to the environment.
- Much of 19th and 20th century chemistry aimed to find ways
to prepare industrial quantities of key chemicals that were needed in
textile and other industries.
- The Solvay process was developed as a way to produce sodium
carbonate, which was and is an essential industrial chemical in many
manufacturing operations.
- Gases that are insoluble may be collected by the downward
displacement of water, soluble gases require more complex arrangements
so as to collect pure samples.
- Destructive distillation is used to prepare some materials,
and usually involves chemical change. It is more heating in the absence
of air than distillation
- One way of separating dissolved material is by dialysis,
which involves filtration through a membrane under some form of active
transport or pressure.
- As a form of separation, sedimentation relies on
differences in density, with more dense solids in a fluid finding their
way to the bottom of a container.
- Filtration relies on differences in the size of particles
or molecules, with sufficiently small particles getting through, while
larger ones are trapped.
- In 1906, Mikhail Semenovitch Tswett (or Tsvett) first used
paper chromatography to separate plant pigments from each other,
allowing them to be analysed.
- Chromatography relies on differences in attraction, whether
from the solvent or the substrate. This applies to paper and gas
chromatography and electrophoresis.
- In 1944, Fred Sanger used chromatography to determine the amino acid sequences in bovine insulin and completed it after ten years of exhaustive work.
The principles of solutions
- Some substances dissolve other substances: solids may dissolve in a
liquid, and solutions may also be formed of gas in liquid, or even
liquid in liquid.
- When a solution is formed, the solute is divided up by
mixing with the solvent until it is in the form of individual molecules
or ions, depending on what it is.
- Solution concentrations can be measured either in terms of a
mass per unit volume, as moles per litre, or as parts per million or
billion, depending on need.
- The maximum concentration of a solution can be predicted
from basic information about the attractive forces involved in the
solute and solvent.
- Solubility relies on differences in attraction between the
particles being dissolved on the one hand, and between the particles and
the solvent on the other.
- A colloid is not quite a solution, but it is not really a
mixture either, given the size and even spread of the suspended
particles that make up the colloid.
- In 1848, Karl von Vierordt established that the osmotic
pressure of a solution is always proportional to the concentration of
solute in that solution.
- Osmotic pressure refers to the force with which a
concentrated solution draws water from a weaker one, or pure solvent,
through a semi-permeable membrane.
- Osmosis involves the flow of solvent from a less
concentrated solution to a more concentrated one, through a
semi-permeable membrane. The solute cannot pass.
- An isotonic solution is one that has the same osmotic
pressure as tissue placed in it, designed so that the cells of the
tissue remain correctly hydrated.
- Ringer's solution is an example of a standard isotonic
solution. It is used to maintain tissues in a living state for
experimental purposes and histology.
- The observation of osmosis in action offers us clear
evidence that atoms exist, since there is no other explanation for the
effects that are seen and measured.
- A polysaccharide is an example of a polymer: a variety of polysaccharides are used in living things to store carbohydrates without making hypertonic solutions.
The principles of crystals
- Solids may be crystalline: the crystal form reflects how the
constituent particles pack together in a regular array. Crystals are
evidence that atoms are real.
- Many compounds form crystals in the solid form, as
identical particles settle into a regular array, offering further
evidence that atoms really exist.
- When the ions in a crystal differ in size, or when water of
crystallization is present, the basic unit may have a shape that
dictates other crystal shapes.
- A crystal's shape and system tells us the shape of the
constituent units, the so-called molecules of the crystallized
substance, which determines how they pack.
- Crystals can form from a melt of metal or magma as it
cools, from a solution as the solvent evaporates, and in a variety of
biological situations.
- A crystal's shape and system tells us about the relative
sizes of the constituent atoms, ions and molecules that are assembled in
its regular arrays.
- Crystallization is a process of dynamic equilibrium, where
particles are being added and subtracted from the crystal all the time
at around about the same rate.
- As crystals form, it is easier for particles to be removed
from exposed positions than from interlinked parts of the array, so
shapes are usually regular.
- As a crystal forms, it is easier for new particles to be
recruited to gaps in the growing array than to link to regular surfaces,
so shapes are usually regular.
- Igneous rocks contain crystals which formed as the hot
magma cooled, allowing particles to link together in regular arrays that
were able to grow in the melt.
- While the elements of a crystal are laid down in regular
arrays, every so often, an irregularity will creep in, producing a small
flaw in the crystal structure.
- The longer minerals take to form the larger and more
perfect the crystals will be, as there will be more opportunities for
flaws and misalignments to be undone.
- Crystals form a lattice of chemical subunits arranged in a
regular array, repeated on a very large scale, and this gives them their
unusual shape properties.
- Every crystal fits into one of the six crystal systems, all
of them defined by the shapes the crystals take, determined by the way
the atoms fit together.
- Every crystal form has axes and planes of symmetry that
define it, and this form of analysis often links two or more different
shapes into a single system.
- Every crystal of a substance fits the same crystal system,
because the crystal is a regular array of atoms, with minor
irregularities, linked by weak bonds.
- When we write NaCl for sodium chloride, we indicate that
the crystal contains equal numbers of sodium ions and chloride ions, and
nothing more than that.
- Substances which form crystals do not exist as molecules:
even if we write NaCl for sodium chloride, there is no such molecule,
but it is convenient to use it.
- In a crystal of sodium chloride, the ions are of comparable
size, and so fill the points of a cubic lattice, which results in a
cubic crystal being formed.
- Crystals come in specific types, determined solely by the
components that make them up. Crystals have no special mystical, psychic
or magical properties.
- The vibrations ascribed to crystals by commercial mystics
refer to the very ordinary piezoelectric effect, which is seen in a few
crystals, but not all.
- The only advice scientists can ever offer to crystal
believers is not to eat the green ones, because they aren't ripe yet, a
bit like crystal power believers.
- Almost everything around you is made of crystals, including
rocks, soil and all metals except mercury, so if crystals have energy
or auras, so does all matter.
- If a piezoelectric crystal is subjected to an alternating
current at a suitable frequency, the crystal may vibrate, just as a bell
vibrates when struck.
- If a piezoelectric crystal is compressed, it will develop a
charge across it. This is a natural property of matter, and not some
mystic form of healing energy.
- Crystals have an amazing healing property, but only for the
sick wallets of crystal sellers, and they have also been used to
resuscitate dying bank balances.
- Diamonds are the hardest natural substance known, and they
can only be scratched by another diamond. A few artificial compounds are
harder than diamond.
- Diamonds may be hard, but they are not tough, so that they
may be broken, and more importantly, they have a tendency to break
(cleave) in specific directions
- When a crystal breaks, the fractures will mainly happen
parallel to the main planes of the original crystal's surface. This is a
function of its structure
- Of the many minerals known to geologists, only about 120
are generally considered to be gemstones, which must have beauty,
durability and rarity to qualify.
- Ornamental gemstones are distinguished from other minerals
simply because they have beauty due to colour (internal or reflected)
and/or pattern.
- Gems may be chemically similar but have different names
based on colour or pattern, as in amethyst and citrine; emerald and
aquamarine, ruby and sapphire.
- Synthetic gemstones are made by humans and have the same
physical, optical and chemical properties (within narrow limits) as the
natural gems they imitate.
- Liquid crystals have different properties from ordinary crystals: they can fall into crystal structures under the right conditions, or fall out of them again.
The principles of chemical bonds
- Molecules are made of atoms linked together by chemical bonds
involving valency electrons and they can be measured: molecules have a
fixed mass, and a set size.
- We consider matter as made of atoms that are grouped into
molecules. We consider atoms as a nucleus surrounded by electrons. The
electrons form chemical bonds.
- In 1921, Charles Bury related the electronic structure of
elements to their chemistry, setting the scene for others to understand
the chemical bond.
- The electrons around the nucleus largely direct chemical
properties, as atoms form covalent bonds by sharing electrons or ions by
gaining and losing them.
- In 1931, Linus Pauling saw resonance bonding in compounds
lacking one single structure and used it to explain the high stability
of symmetric planar molecules.
- Chemical change usually involves electron transfer, which
requires the application or release of energy as chemical bonds are
changed, broken and formed.
- The shape of a molecule can be predicted from our knowledge
of its chemical bonds and the sizes and numbers of the atoms involved
in forming it.
- Bonding between the atoms in chemical compounds takes
different forms: ionic bonds, metallic bonds and covalent bonds being
the most common forms encountered.
- Molecules may have ionic or covalent bonds, depending on
the affinities of their components for electrons. Gradations between the
extremes are also possible.
- Ionic compounds may be considered for calculation and
prediction purposes as if they are molecules, even though they never
exist in nature as molecules.
- Some substances decompose when heated, because the bonds
holding the compound together were overcome by the heat energy that was
externally applied.
- Decomposition is a chemical change producing new compounds:
compounds may decompose when energy is applied, or when energetic bonds
between atoms break down.
- Combustion is a chemical change, usually happening in the
presence of oxygen, but it is also able to happen in chlorine, which is
an excellent oxidizer.
- Mass is always conserved in chemical reactions: if the
products appear to have a different mass, one product was probably lost
in the form of a gas.
- One common form of chemical reaction is the redox reaction,
where one of the reactants is oxidized and another reactant is reduced
at the same time.
- Extracting metal from ore involves reducing the metal from
an oxidized state to a neutral state, while the reducing agent is
oxidized at the same time.
- Energy affects molecules and ions, leading to change as new
linkages and combinations are formed, because the energy is able to
influence bonds.
- There is an enthalpy of formation associated with every
chemical reaction, and this can be predicted, given sufficient knowledge
of the bonds involved.
- Chemical change involves atoms changing partners in either a
simple or a complex way to form new compounds. Energy is always
involved in chemical changes.
- Most reactions need energy, or else they release energy: an
endothermic reaction absorbs energy, while an exothermic reaction
releases energy.
- In 1800, William Nicholson and Anthony Carlisle use
electrolysis to separate water into hydrogen and oxygen, using the
battery of Alessandro Volta.
- Electrolysis is a chemical change, involving the
application of energetic electrons to ions, while the electrical energy
strips electrons from other ions.
- In 1834, with the increasing use of electrolysis, Michael
Faraday introduced the convenient terms electrolyte, electrode, anode,
cathode, ion, cation and anion.
- Heating of a substance can bring about chemical change,
because heat is a form of energy, and so is able to make changes in the
existing bonds.
- Some chemical reactions can produce useable energy, as in
the heat produced in a flame, or the electricity produced from chemical
energy in a cell.
- The simple structures of many molecules are reflected in
their equally simple formulae, but simple formulas can sometimes be
misleading if taken literally.
- We can write a molecular formula to represent a compound,
but the fact that we use a molecular formula does not imply that such a
molecule necessarily exists.
- We can calculate empirical formulae of all sorts of
compounds, but just because we use an empirical formula, that does not
imply that such a molecule exists.
- We can draw structural diagrams of molecules, but our use
of a structural diagram does not imply that such a molecule as the one
drawn actually exists.
- Chemical analysis often relies on knowing what chemical
changes will happen in given conditions, so that each reaction (or lack
of one) provides information.
- The van der Waals forces make atoms cling and stick together, and this is why gases fail to perform in the ideal way laid down by the gas laws.
The principles of metals
- A metal is malleable and usually ductile, metals have good
conductivity: they also have a lustre, they conduct heat and
electricity, and form positive ions.
- A simple form of iron is cast iron, but this is less
valuable than steel, which is far more useful both for tools and
weapons, and also in construction.
- Most metals are found as compounds called ores: one ancient
source of pure iron ore is bog iron, which was exploited by the
Vikings, among others.
- Most metals are affected by corrosion, particularly those
high on the activity series, though a few like aluminium can be
protected by a tough coating of oxide.
- Galvanized iron does not rust when it is scratched, but
tinplate rusts readily, reflecting the different reactivities of zinc
and tin, compared with iron.
- Cathodic protection depends on metals having different tendencies to be oxidized: a zinc block attached to a hull will protect a steel ship from corrosion.
The principles of acids and alkalis
- An acid can be regarded for practical purposes as a proton donor,
while an alkali, sometimes called a base, can be thought of as a proton
acceptor.
- In 1884, Svante Arrhenius and Wilhelm Ostwald independently
defined acids as substances which release hydrogen ions when they are
dissolved in water.
- In 1923, Johannes Bronsted defined acids as substances
acting as proton sources, and bases as substances acting as proton
acceptors, regardless of the solvent.
- Neutralization is the reaction of an acid with an alkali,
and in essence, it involves hydrogen ions combining with hydroxyl ions
to form water.
- Acids and alkalis are of different strengths as measured on
the pH scale, which is a logarithmic scale based on the concentration
of hydrogen ions.
- The pH of a solution may be assessed with indicators, which
are organic dyes that can add or lose hydrogen ions, and then change
colour as a result.
- Robert Boyle described in his 'experimental History of
Colours' how some vegetable dyes change colour in acids and alkalis and
introduced litmus.
- As a general rule, acids react with metals, releasing
hydrogen. To be more precise, the stronger acids react with the more
active of the metals.
- A buffer solution is one that retains a fairly constant pH,
even when acid or base is added to the solution, because it is able to
absorb or donate protons.
- Some parts of the world are troubled by acid rain, an effect which is caused when acidic gases produced by burning fuels react with water vapour.
The principles of rates of reaction
- Every reaction proceeds until an equilibrium point is reached.
Depending on other conditions, this may be reached rapidly or slowly,
but it can be influenced.
- Chemical equilibrium is always a dynamic equilibrium, with
changes in one reaction direction being influenced by changes the other
way restoring the status quo.
- The study of chemical equilibrium is an important part of
chemistry because most chemical reactions proceed only to equilibrium
and halt after that is reached.
- The equilibrium point often changes with physical
conditions such as the operating temperature, pressure, and the
concentrations of reactants.
- The speed of a reaction to equilibrium changes with
physical conditions such as temperature, pressure, and the surface areas
and concentrations of reactants.
- Chemical changes occur at different speeds, which can be
affected by the presence of a catalyst, which affects the rate of
reaction, but is not changed.
- A catalyst is something which influences the rate at which a
chemical reaction proceeds to equilibrium, but which is not itself
changed by the reaction.
- A catalyst can be used to increase the speed at which an
equilibrium is reached, but the catalyst does not influence the actual
equilibrium point in any way.
- Enzymes operate as catalysts best under very specific
conditions of temperature and acidity, and they can all be destroyed by
high temperatures.
- Enzymes are found in all living things: they are proteins,
catalysts that are coded for by individual genes. They control all
biochemical pathways in the cell.
- An enzyme is a protein which operates in a biochemical
reaction in the same way as a catalyst in a chemical reaction, and like a
catalyst, remains unchanged.
- Every chemical reaction is associated with an equilibrium
constant, which may be predicted with reasonable accuracy, using
standard known values.
- In 1803, Claude Berthollet stated that the proportions of
the reactants affects the direction in which chemical reactions take
place, changing the equilibrium.
- The speed of a reaction varies with the surface area of the
reactants, as this increases the frequency of particle contact,
increasing the chances for reaction.
- The reaction of an equilibrium to changes in physical
conditions is described by Le Chatelier's principle: the equilibrium
moves to accommodate the changes.
- The equilibrium point of a chemical reaction may be
influenced by changing the physical factors like heat and pressure to
favour one reaction over another.
- In 1876, Josiah Gibbs began writing on phase equilibria,
the free energy as the driving force behind chemical reactions, and
chemical thermodynamics in general.
- Some chemical reactions only take place if the energy barrier is overcome by heat or a catalyst: once started the reaction provides the energy to keep it going.
The principles of carbon chemistry
- Carbon chemistry is also called organic chemistry, because all of
the key compounds found in living things contain carbon. Some carbon
compounds are inorganic.
- In 1828, Friedrich Wöhler synthesized urea, reacting lead
cyanate and ammonia and heating the ammonium cyanate, reducing the
special status of organic compounds.
- William Perkin made the first of the aniline dyes in1856,
while investigating coal tar, a left-over from the manufacture of coal
gas, starting a new industry.
- In 1924, methanol, traditionally made by wood distillation,
was able to be made from carbon monoxide and hydrogen in the presence
of a suitable catalyst.
- Carbon chemistry shows parallels and differences when
compare with other group 4 elements, but the others do not form long
chains as carbon does.
- Carbon atoms can form a total of four bonds with other
nearby atoms, so that they can link together to form chains, rings,
nets, sheets and balls.
- In 1874, van't Hoff and Le Bel proposed a 3-dimensional
stereochemical representation of organic molecules and proposed a
tetrahedral carbon atom.
- Hydrocarbons can be altered with a substitution reaction,
where one attachment (such as hydrogen atom) is replaced by another
(such as chlorine atom).
- The carboxyl group, generally written -COOH, is found in
all carboxylic acids, along with a functional group which accounts for
any observed differences.
- A polymer is made from monomers, but different polymers may
use the same monomer in different ways, by linking it differently or
having more or less branching.
- Carbohydrates are compounds containing the elements carbon,
hydrogen and oxygen that contain a lot of energy and that are easy to
store as polymers.
- Amino acids may be assembled into a polypeptide chain which
may then be folded down and held in shape by disulfide bridges, when it
is referred to as a protein.
- Proteins are polypeptides, that is, polymers made of
strings of amino acids. The actual properties of a protein depend on how
the polypeptide folds.
- DNA has four bases (adenine, cytosine, guanine and thymine)
on a sugar phosphate polymer backbone. RNA has a similar structure,
with uracil instead of thymine.
- In 1990, Krätschmer, Lamb, Fostiropoulos, and Huffman
discovered that buckminsterfullerene can be separated from soot because
it was soluble in benzene.
- In 1985, Harry Kroto and his colleagues discovered the unusual stability of the carbon-60 buckminsterfullerene molecule and deduced its structure.
The principles of applied chemistry
- The chemical industry is mostly based on just a few simple
compounds. Sulfuric acid is probably the most important, with chlorine
and caustic soda close behind.
- Only one of the key industrial chemicals, caustic soda, has
a simple substitute available, in the form of sodium carbonate, used
since ancient Egyptian times.
- In 1723, the use of lead in rum stills was banned by the
Massachusetts legislature, after drinkers had complained of stomach
problems and partial paralysis.
- In 1783, Nicolas Leblanc developed his Leblanc process to
make sodium hydroxide and sodium carbonate from salt, making soap-making
possible on a large scale.
- In 1799, Charles Macintosh invented bleaching powder, made
when chlorine is absorbed by dry slaked lime. It was patented in the
name of Charles Tennant.
- In 1865, the first plastic, parkesine, was made by
Alexander Parkes from nitrocellulose, softened by vegetable oils and
some camphor (also called xylonite).
- Robert Bunsen analysed igneous rocks from Iceland and Armenia and showed the rocks came from sources which were chemically identical, founding geochemistry.
The principles of biochemistry
- The laws of chemistry affect animals and plants in many ways because
the operations of every cell are, at the simplest level, chemical
operations.
- Biochemistry describes the many ways that chemistry is
involved with maintaining life inside the cell, and also outside the
cell, all around the organism.
- The basis of all life is the translation of the genetic
code into the chemicals of life, in particular, into the formation of
proteins in particular ways.
- All cells contain lipids, proteins, nucleic acids and
carbohydrates: some are absorbed, others are formed within the cell from
absorbed material.
- A simple sugar is a monosaccharide: two monosaccharides can
be joined to form a disaccharide such as sucrose, which can be split by
various enzymes.
- Larger chains of monosaccharides can be formed: these are
called oligosaccharides and polysaccharides. These are important in food
storage in many cases.
- The properties of a carbon compound can be altered by
changing or adding a functional group which changes its size, shape and
charge distribution.
- Amino acids have common and different parts: the different
parts make the proteins different, and the common parts allow the amino
acids to form peptide bonds.
- Much protein chemistry is explained by the lock and key
model, where a protein must have the right shape and charge distribution
to fit another molecule.
- In 1934, J. D. Bernal showed that giant molecules, such as
proteins, can be studied by applying X-ray crystallography to the
crystalline material.
- In 1952, Sanger, Tuppy, and Thompson completed their
chromatographic analysis of the insulin amino acid sequence. Sanger and
Tuppy reported the B chain in 1951.
- Fred Sanger and Hans Tuppy reported the 30 residues of the
insulin B-chain in 1951, now many million bases are added each year,
making bioinformatics essential.
- In 1953, Max Perutz and John Kendrew determined the
structure of haemoglobin using X-ray diffraction patterns taken from
crystallized haemoglobin.
- The genetic code of any organism specifies the construction
of proteins by setting the order in which amino acids are strung
together in the polypeptide.
- DNA is transcribed to messenger RNA and that is then
translated into a protein, following the standard pattern of the genetic
code in all organisms.
- In 1883, Pierre Émile Duclaux introduces the custom of
naming an enzyme by adding "-ase" to the name of the substrate on which
its action was first reported.
- In 1897, Gabriel Bertrand, studied the hardening of lacquer
(laccase) and used 'coenzyme' for inorganic substances necessary to
activate certain enzymes.
- In 1935, Rudolf Schoenheimer used deuterium-labelled fat
compounds to examine the fat storage system of rats and showed that
about half the fat was stored.
- In 1939, Ruben, William Zev Hassid and Martin David Kamen
first applied radioactive tracers to following the biochemical steps
involved in photosynthesis.
- In 1941, Ruben, Randall, Martin David Kamen, and Hyde
reported that the oxygen liberated in photosynthesis comes from water,
and not from carbon dioxide.
- Some chemicals interfere with metabolic pathways within
living cells: if they and their interference cause serious damage, we
call these chemicals poisons.
- Some poisons are useful as pesticides, which selectively
kill problem organisms such as microbes, plants and insects, but they
can also cause problems.
- Every poison can have an LD-50 calculated for it, the concentration which will, in theory at least, kill half of a test population exposed to it.
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© The author of this work is Peter Macinnis, who asserts his sole right
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