The Chemistry SPLATs

 

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. 

There are other SPLATS to be found, but you will need to go back to the main SPLATS page to find the links.

© The author of this work is Peter Macinnis, who asserts his sole right to the product as it is packaged here, recognising that many of the ideas are common. You are free to use this as a model to do your own version. Copies of this whole file or site may be made and stored or printed for personal or educational use. You can contact me at macinnis44@gmail.com, but only if you add my first name to the front of that email address — this is a low-tech way of making it harder to harvest the e-mail address I actually read.