Absorption In chemistry absorption can mean two things: Firstly it can imply that powerful forces exist holding two substances together, and that seperation of the two is not easily accomplished. Secondly it can mean absorption of heat, light etc.. . The absorption of ultraviolet, visible and infrared radiation is the basis of some forms of spectrometry which can be used to identify different chemical compounds. See also infrared radiation.
Acid A substance that when dissolved in water dissociates and can donate a hydrogen (proton) to another molecule. Examples include sulphuric acid and nitric acid. Under these conditions nitric acid dissociates according to the following equation:
In water the protons attach themselves to the water molecules, giving the following equation:
Actinides This is a group of elements within the periodic table and are also known as the transuranics. The name refers to those elements with increasing atomic no. from actinium, which all have similar chemical properties, like the lanthanides. The first few members of the group are the naturally occuring elements actinium, thorium, proactinium and uranium. Beyond this elements have been made artificially by radioactive bombardment. These artificial elements are unstable, some have very short lifeimes and undergo spontaneous radioactive decay.
Adhesive Any compound that can stick two surfaces together is classified as an adhesive. Simple adhesives are of cellulose, starch and rubbers. Modern adhesives are based upon complex polymeric materials. The adhesive is spread in an unpolymerised form, and the adhesive properties increase as polymerisation occurs between the two surfaces.
Adiabatic A chemical or mechanical process which takes place without heat entering or leaving the system. The term is only applicable to enclosed and isolated systems - so in essence is idealistic and purely theoretical and is important in the study of thermodynamics.
Adrenaline This was the first naturally produced hormone to be isolated it a pure state. It is known as epinephrine, but its chemical name is 1-[3,4-dihydroxyphenol]-2-methylaminoethanol. Its main action is to raise blood pressure, producing a faster pulse rate.
Adsorption If any compound, solid, liquid or gas, is loosely held by weak attraction to the surface of a solid it is said to have undergone adsorption. This process is much weaker and less permanent than absorption.
Air The air that we breathe is a mixture of gases. The composition of dry-air at sea level is shown below:
Alchemy Several of the great Greek philosophers considered all matter to be composed of four basic "elements", fire, air, earth and water, and that all materials were had these components mixed in different proportions. If this theory was true, then it was believed that all substances could be converted (transmuted) into each other by varying the proportions of the mixture. This tansmutation theory was the basis of Alchemy from approx. 300 B.C. to 1500 A.D., after which it slowly gave way to the more scientific concepts of chemistry from the 17th century onwards. The alchemists represented their "element" by a variety of symbols (see below), some of which were based on astrological signs
They were mainly concerned with trying to turn base metals into gold and looking for the elixir of life although they also developed medicinal drugs, developed couterfeiting techniques and the debasement of precious metals.
Alcohol An organic compound which has the general formula CnH2n+1OH, they consist of hydrocarbon chains terminated by hydroxyl groups, O-H. Smaller members are water soluble, flammable and are useful as organic solvents and fuels. As with hydrocarbons, each member differs from the previous by an additional -CH2- group. Alcohols with branced chains are also possible. Some of the simpler alcohols are listed below:
Aldehyde An organic compound containing the -CHO group (see below). An example of these distinct aromatic compounds is formaldehyde.
Alicyclic compounds An alicyclic compound contains rings of -CH2- units joined by single bonds. Their general formula is CnH2n, the simplest member being cyclopropane. An example of these compounds is cyclohexane (see below):
Alkali A water soluble hydroxide on one of the alkali metals. The term is virually synonymous with the term base. An example is Sodium Hydroxide, NaOH.
Alkali metals Group I of the periodic table consists of the alkali metals. They are the most electropositive elements known, are monovalent, have low melting points and react violently with water.
Alkaline earth metals Group II of the periodic table consists of the alkaline earth metals. They are bivalent and react with water to produce water soluble hydroxides.
Alkaloid A naturally occuring organic compound containing nitrogen that acts as a base. Many alkaloids are physiologically active and can be used in small quantities as medicines, but if taken in larger doses they can be extremely poisonous. An example is caffeine.
Alkanes This is the correct chemical term for compounds known as paraffins. They are considered the simplest organic compounds and are a family of chain hydrocarbons having the general formula C2H2n+2. All of the bonds are single bonds (-C-H-, and -C-C-). The chains can be straight or branched. The smaller members (less than 4 carbons) are gases, while larger ones (five to seventeen carbons) are liquids. Beyond seventeen carbons the alkanes are waxy solids. Some simple alkanes are listed below:
Alkenes These compounds are similar to alkanes, in that they can be straight or branched aliphatic hydrocarbons. The only difference is that the alkenes (also known as olefins) contain a carbon-carbon double bond, and have the general formula C2H2n. The simplest group member is ethene which is a gas. The double bond can be anywhere within the length of the carbon chain, resulting in a large number of possible isomers. The double bond means that these compounds are "unsaturated" and react readily with compounds capable of adding across the double bond. Some simple alkenes are listed below:
Alkynes These compounds are also similar to alkanes. They have the general formula C2H2n-2 corresponding to carbon chains with a triple carbon-carbon bond included. The simplest member of this family is ethyne (also known as acetylene). The triple bond makes these compounds very reactive. Some simple alkynes are listed below:
Allotropy Certain chemical elements have the ability to exist in two or more different structural forms known as allotropes. These allotropes may possess different physical properties such as density and melting points. Allotropic elements include carbon, tin, phosphorus and sulphur. Each allotrope is stable within a certain range of temperature and pressure only, and under certain conditions an allotrope can be converted into another.
Alloy An alloy consists of an intimate mixture of two elements, usually metals to give a metal compound or solid solution. Bronze is an alloy of copper and tin and brass on of copper and zinc. By varying the composition it is possible to alter the chemical and physical properties of the alloy such as conductivity, ductility and corrosion resistance.
Alpha particles These are particles possessing a positive charge, and are emited from radioactive elements. The particles are actually helium nuclei, ie. helium atoms that had lost their outer electrons. The study of the alpha particle played a major part in the development of modern atomic theory. Rutherford bombarded other elements with alpha particles to produce nuclear disintegration.
Alum An alum is a double salt comprising a sulphate salt of a monovalent element, with the sulphate salt of a trivalent element. The most well known example is potash alum (aluminium potassium sulphate) KAl(SO4)2.12H2O which is used to clear murky water.
Amalgam Liquid mercury has the ability to dissolve other metals to produce alloys and these alloys are called amalgams. Amalgam examples are gold/mercury, silver/mercury and copper/mercury all of which are used in dentistry.
Amide An organic compound containing the -CONH2- group (see below). Also see peptide.
Amine An amine is a distinctive smelling organic compound with one or more of the hydrogen atoms in ammonia replaced by organic groups. There are three classes of amines, dependant on the number of hydrogens replaced (see below):
The organic groups can be aliphatic, alicyclic or aromatic, and some common amines are listed below:
Amino group An organic compound containing the -NH2- group. Substances which contain this group are called amines. Examples include urea, and trimethylamine.
Amino acid A large class of substances with molecules including the amino and carboxyl groups.In the human body, amino acids are joined together to form long chains as part of the structures of proteins. Because they possess two functional groups, amino acids exhibit both acidic and basic characteristics. Each amino acid has an abbreviation when in a protein chain, so that the protein GlyAlaVal would indicate that a molecule of Glycine is joined to one of Alanine which is in turn joined to one of Valine. A list of the more common amino acids are given below:
Anhydride These are compounds formed by the removal of water or Hydrogen and Oxygen together from another substance. In inorganic chemistry most anhydrides are formed by the loss of the water of crystallisation. eg. Copper(II) sulphate is a blue hydrated salt with the formula CuSO4.5H2O, but if heated, the water is driven off leaving the colourless anhydrous salt CuSO4. In organic chemistry an anhydride is usually the result of the loss of a water molecule from a dicarboxylic acid, eg. from phthalic acid to give phthalic anhydride (see below):
Anion A negatively charged ion or group of atoms.
Antioxidant A substance which decrease the rate at which another substance is oxidised. An example includes BHA.
Aromatic compound A substance containing one or more benzene rings. These compounds although unsaturated do not undergo normal reactions for unsaturated compounds as shown by their saturated open-chain analogues. This ability is related to the way in which their bonding electrons are spread evenly over the planar ring. Substances classified as being aromatic include those with one benzene ring such as:
- or several rings such as:
Certain other compounds can posses aromatic character - ie. they react in an aromatic manner even though they do not have the six-membered carbon ring. This group of compounds includes:
Atactic A polymer is atactic if the groups attatched to the backbone are not arranged in any regular geometric pattern. Also see Isotactic.
Atom The smallest part of an element that retains its properties. It is possible to "split" the atom up further into components; protons - which have a positive charge, electrons, which have a negative charge and neutrons which have no charge. The simplest atom is hydrogen, which consists of a single proton nucleus and has a single electron forming an orbit or shell around the proton. The next simplest is helium, with two protons and two neutrons in the nucleus with two electrons orbiting within the shell - see selow for diagram:
In all atoms the number of protons and electrons are the same but the number of neutrons can vary. Most of the mass of an atom is composed of the protons and neutrons, while the different isotopes of the same element vary in their number of protons, neutrons and electrons in the atomic structure. In some elements the arrangement of protons and neutrons in the nucleus is unstable, and the atom may disintegrate forming radioactivity.
Azo dye An azo dye is one of an extensive range of synthetic organic dye made from aniline, by first converting it with sodium nitrite to a diazonium chloride salt which is then reacted with other aromatic amines, phenols and sulphonic acids. The well known indicator methyl-orange is formed by making the diazo salt of sulphanilic acid, and reacting the product with dimethylaniline (see below):
All azo compounds have the general formula Ar-N=N-Ar' with the characteristic -N=N- group in the middle.
Base A substance that reacts with acid to produce a salt and water only. It does this by accepting a hydrogen ion from the acid. An example is ammonia which accepts a proton to become the ammonium ion - NH4+
Beta particles Radioactive elements can emit several types of radiation. Beta particles are very fast moving electrons. The particles have a velocity of between 30-99% speed of light, and it is this velocity which gives the beta particles greater penetrating power than alpha particles.
Bond A chemical link between two atoms. In an ionic bond the attraction is between opposite charges on two neighbouring ions. In a covalent bond the two atoms share a pair of electrons.
Carbanion This is an abbreviation of "carbon anion", and is applied to negatively charged ions that are believed to occur during organic reactions. The carbanion then reacts with positive species to produce new products. To acquire a negative carbon ion it is necessary for the atom to retain two electrons forming a bond between itself and another group - see below:
Carbonyl group An organic compound containing the >CO group (see below). When a hydrogen atom is attached to the carbon, the resulting compound is known as an aldehyde. When only carbon atoms are attached, the resulting compound is known as a ketone. See also carboxyl group and amide group.
Carboxyl group An organic compound containing the -COOH group (see below), Where a carbonyl group is attached to a hydroxyl group. See also carboxylic acids.
Carboxylic acid A substance containing the carboxyl group. The carboxylic hydrogen can be lost as a hydrogen ion, so these substances are also acidic. An example includes acetic acid.
Carcinogen A substance capable of causing cancer in living organisms. It includes substances such as blue asbestos (crocidolite), which is a mineral, and benzene. Benzene has been used extensively for decades in chemistry and strict saftey guidlines must now be followed befrore it is used. Any new pharmaceutical, cosmetic or food chemical has to be checked to ensure that they are not carcinogenic.
Catalyst A substance that changes the rate at which a reaction equilibrium is attained, without itself being consumed. Catalysts can increase the rate of reaction (positive catalysts) or decrease them (negative catalysts or inhibitors).
Cation A positively charged ion or group of atoms.
Chain reaction A reaction where the product of one step is a reactant in a later step, which produces a reactant for a later step, and so on.
Chiral Means "handedness" - A chiral or asymmetric molecule is one which can be distinguished from its mirror image. An example includes lactic acid.
Cis-trans isomerism Compounds with double bonds, or alicyclic rings can exhibit isomerism, due to the attached groups lying above or below the plane of the oduble bond or ring. The "cis" compound is the one with the groups on the same side of the bond, and the "trans" has the groups on the opposite sides. The different isomers have different physical and chemical properties. Examples are fumaric acid/maleic acid and 1,3-dimethylcyclohexane - see below:
Combustion Combustion is the combination of a substance with oxygen in the presence of a flame accompanied by the production of heat and light. Combustion requires a supply of both fuel and oxygen (air) and can take place in the open atmosphere such as an open fire, or in a closed system, such as a car engine.
Condensation reactions This is mainly an organic reaction where a simple molecule such as water or ammonia is eliminated when two molecules combine to produce another compound. A typical reaction is the esterification of an acid by an alcohol - in this case water is eliminated - see below:
Condensation reactions reaction play a major part in the polymer industry for the synthesis or artificial polymers.
Cross-links To increase the rigidity and density of synthetic polymers groups are introduced into the monomer molecules which enable bonds to form between polymer chains - this is known as cross-linking. The degree of cross-likning can have a marked effect on the physical properties of the final product. An example are the silicones - they can vary from oils (low degree of cross-linking) to waxes (high degree of cross-linking).
Crystal A discrete solid where the atoms,ions or molecules are arranged in an ordered 3-dimensional structure. The regular structures have the ability to "bend" or diffract beams of X-rays, and this aspect of crystallography is an extremely helpful tool in structure determination.
Cyclic compounds A cyclic compound is one where the atoms are joined together so as to form a closed ring.
Decomposition Where chemical compounds are broken up into simple molecules and even as far as their original elements. These processes are normally irreversible. An example of decomposition is when ammonium nitrate is heated. This produces nitrous oxide and water which are unable to recombine - see below:
Detergents These are organic chemicals designed to clean surfaces or objects. They do this by reducing the surface tension and suspend dirt in suspension from the object to be cleaned. Early detergents were long chain alcohol derivatives of sodium sulphate salts, such as sodium lauryl sulphate CH3(CH2)11O.SO2.ONa they were superseded by alkyl benzene sulphonates but these could not be broken down easily by bacteria at sewage works so these were eventually replaced by more eco-friendly detergents. Detergent molecules come in two parts - the sulphate or phosphate end (water soluble hydrophilic portion) and an organic hydrocarbon chain (water insoluble hydrophobic portion).
Diazo compounds This is a series of organic compounds possessing the general formula Ar-N=N-Y, where Ar is an aromatic group and Y is any group linked to the nitrogen except via a carbon atom. They are different from the azo compounds which have the general formula Ar-N=N-Ar'. Diazo compounds are formed from amines by a two stage diazotisation reaction. Stage one is the conversion of an aromatic amine into a diazonium chloride salt using cold sodium nitrite and hydrochloric acid - see below:
The second stage is the reaction of the diazonium chloride salt with an appropriate compound - such as another aromatic amine, eg. the reaction with p-toluidine - see below:
Distillation The separation and purification of a mixture of components by vapourisation followed by condensation, based on the different volatilities of each component. A typical experimental set up for distillation is shown below:
Drug Any chemical compound used for medicianal purposes can be considered a drug. There are naturally occuring substances such as ethanol and caffeine as well as synthetic drugs such as aspirin and amphetamines. In general the term "drug" is used for compounds that can cause addiction with emphasis on narcotics.
Dyes Dyes are chemical compounds that can attach themselves to fabrics or surfaces to give them colour. Most dyes are complex organic molecules and need to be resistant to many things such as the weather and the action of detergents. Indigo, otained from plants was being used by the Egyptians 5000 years ago, and natural dyes obtained from plants and animal sources are stil used today. In 1856, Perkin developed the first synthetic dye based upon aniline.
Electromagnetic waves All matter absorbs and emmits radiation covering a broad band of frequencies and wavelengths. This electromagnetic radiation has the velocity of the speed of light (2.998 x 108 ms-1) and arises from the vibrating electric charges in atoms and bonds. The range of wavelengths, also known as the electromagnetic spectrum is shown below:
Electron An elementary negatively charged particle orbiting within an atom, the electrons are arranged in shells - and it is the outermost shell electrons which take part in bond formation.
Electron pair Two electrons within one orbital with opposite spins responsible for a chemical bond. See also lone pair.
Emulsion A dispersal, with a variety of industrial uses of one liquid as small particles in another liquid. An example would be milk.
Enzyme A naturally occuring protein that fascilitates a specific biochemical reaction; a biological catayst.
Ester A volatile fruity odoured product of the reaction between a carboxylic acid and an alcohol.
Exothermic reaction The majority of chemical reactions are accompanied by the evolution of heat - these is known as exothermic reactions. The reaction between an acid and a base is exothermic, it is possible to feel the temperature change when one is added to the other - see below:
A rapid exothermic reation results in an explosion, as occurs when TNT explodes.
Fatty acid A naturally occuring, usually in fats, monobasic carboxylic acid, with a long hydrocarbon tail chains.
Ferromagnetism Many substances are found to be magnetic, in that they are attracted by magnetic and electric fields, but it is found that the metals iron, cobalt, nickel and a number of alloys posses a greater level of magnetism than other substances. This powerful magnetism is called ferromagnetism, and is due to a large magnetic moment in the atoms of the metals due to an unbalanced spin of the electrons in their inner orbits.
Fluorescence The slow emission of longer wavelength light following the absorption of shorter wavelength radiation. Fluorescence is common with aromatic compounds with several rings joined together. Phosphorescence is similar but may persist long after the stimulating radiation is extinguished.
Gamma rays One of the three types of rays produced by radioactive disintegration, but gamma rays are the only one comprised of electromagnetic radiation. Gamma rays have a very short wavelength, and have the greatest penetrative power of all radioactive emissions.
Glycols Glycols are compounds that have two hydroxyl groups present in each molecule. The simplest member is ethylene glycol - see below:
Halogens This important group of elements occupies Group VII of the periodic table. Its first element, fluorine, is the most strongly electronegative element known. All halogens are electron defficient and readily share electrons with other elements to staisfy their valency needs, eg. they all form compounds with hydrogen, with the formula HX (where X=halogen)
Heavy water A molecule of water contains two atoms of hydrogen and one of oxygen. Most water comprises of hydrogen/oxygen but a small percentage is composed of another hydrogen isotope, deuterium and oxygen. Deuterium differs from hydrogen by having one neutron in the nucleus of each atom. Deuterium water is given the formula D2O. There is approx. 1 part in 5000 D2O in normal water and it can be concentrated by electrolysis. D2O had a higher boiling point (101.4 °C) and melts at 3.6 °C
Heterocyclic molecule A molecule containing at least one ring of carbon atoms, and which also has at least one atom from a different element, (nitrogen, sulphur, oxygen etc..) within the ring. Examples are shown below:
Hydrocarbon A molecule comprised solely of carbon and hydrogen. The simplest example is Methane.
Hydrogen bond A bond formed by a hydrogen atom to an electronegative atom, and is denoted X---H-B.
Hydrogen ion The ion which is left when the hydrogen atom loses its electron, forming a proton. In water the hydrogen ion binds to the water molecules, producing H3O+. Compound which exhibit hydrogen bonding include water and amines.
Indicators A number of complex organic molecules can change their molecular structure and colour when faced with different pH conditions. The most well known indicator is litmus, which is a mixture of vegetable dyes. A list of common synthetic dyes is given below:
Infrared radiation Electromagnetic radiation whose wavelength is longer than that of visible light, and is responsible for the transmission of radiant heat.
Ion An electrically charged atom or group of atoms. If an atom or molecule gains an electron - it becomes a negatively charged anion, or if it loses an electron it becomes a positively charged cation.
Isomerism If a molecule possesses the same molecular formula, but the atoms are arranged in a different way, then they are called isomers. Isomers have different physical and chemical properties from each other. Optically active isomers differ only in the fact one is the mirror image of the other, as shown with lactic acid below:
Many isomers occur as a result of different substituents occupying different positions on a benzene ring - see below:
Isotactic Means geometrically regular. A polymer is isotactic if all of the groups attched to the back bone are arranged in the same geometrical pattern. See atactic.
Isotopes All atoms of the same element posses the same no. of protons and electrons but not neccarily the same no. of neutrons. So all atoms of an element will react in the same way, but they can differ in their molecular masses. Atoms of the same element with different masses are known as isotopes. Hydrogen has three isotopes. 99.98% of all hydrogen has one proton and one electron, while 0.02% of hydrogen has one proton, one neutron and one electron. This isotope is called deuterium. There is also a trace of a third isotope, tritium, which has two neutrons in its nucleus.
Ketone An organic compound containing the carbonyl group, >C=O, to which other carbon atoms are attached. Ketones are extremely useful as solvents and paint components. An example is Butanedione.
Lanthanides This is a group of fifteen closely related elements and are known as the rare earth or "inner transition" elements. They are so alike that they are difficult to seperate from each other and usually all occur together in nature.
Lipid A naturally occurring substance soluble in organic solvents but not in water.
Molecule A molecule is two or more atoms joined together by chemical bonds. This may result in two atoms of the same molecule, such as chlorine, Cl2, or by combining elements as in ammonia, NH3. A molecule can be considered the smallest unit representitve of that compound which possesses all its properties.
Lone pair A pair of electrons not involved in bond formation.
Monomer A monomer is a starting material or single unit from which a polymer is built. It refers to the repeat units that make up the polymer chains. Ethylene is the monomer for polyethylene and styrene for polystyrene.
Neutron One of the three fundamental particles which form atoms, the neutron has the mass of a proton but no electrical charge. Neutrons are emitted when large atomic nuclei are bombarded with alpha particles.
Noble gases This collection of elements make up Group 0 in the periodic table. They were known as inert gases for many years but that has changed with the reports of noble gas compounds. They are all gaseous elements found in the atmosphere, except for radon which is formed from the radioactive decay of uranium. The elememts are inert due to their stable electronic configuration. The gases are useful as inert atmospheres for reactions that must exclude oxygen, for balloons (helium) and for lighting displays.
Oxidation This is a reaction with oxygen, as in combustion. An oxidized molecule is generally one that has lost electrons. Reduction also takes palce during oxidation - if one substance is oxidised then anothr must be reduced.
Parrafin See alkanes.
Peptide An organic compound containing the group -CONH (see below), examples of which are polypeptides.
Periodic table Early alchemists understood that certain elements could be grouped together due to the properties that they had. But it was not until the 18th century that Lavoisier tried to classify the known elements. It took another 100 years and a lot of trial and error for Mendeleev to propose a real foundation for the modern periodic table. He arranged the elements in a table according to relative atomic mass and left gaps where an element did not match. By doing this he could predict where a new element should come and what properties it should have.
pH Acidity and alkalinity of aqueous solutions are axpressed in terms of pH. This is a measurement of the hydrogen ion concentration of the solution. Mathematically it is expressed as:
The pH scale of 0-14 covers the range from strong acid to strong base. A neutral solution has the same number of hydrogen ions and hydroxyl ions and this corresponds to pH 7. Values higher than pH 7 are alkaline, whereas if they are lower than pH 7 they are acidic.
Phenol An organic substance in which a hydroxyl group is attached directly to a benzene ring. An example is vanillin.
Photochemical reaction A chemical reaction can be enhanced when induced by light, just as some are speeded up by catalysts. Chlorine is one of a number of substances that undergo photochemical reactions. In sunlight, chlorine will react with carbon monoxide to produce the poisonous gas phosgene:
A large number of organic reactions are carried out by irradiating with ultraviolet light.
Photon All matter absorbs and emits electromagnetic radiation in discrete small quantities called photons. The energy of a photon (E) varies withthe frequency of the radiation according to:
- where h is a constant known as Planck's constant.
Polymer A polymer is a long chain molecule or a complex 3-dimensional lattice produced by the reaction of simple compounds with each other. There are two types of poymerisation. The first, where compounds open a double bond and link together via the radicals formed is called addition polymerisation. eg. the poylmerisation of propylene to polypropylene:
The other main type of polymerisation is condensation polymerisation, where as with condensation reactions, a simple molecule is eliminated during the formation of the polymer, eg. the reaction between adipic acid and hexamethylenediamine to produce nylon:
Protein A molecule comprised of long chains of amino acid molecules. Proteins, which include enzymes, are polypeptides.
Proton One of the three fundamental particles in atoms. Protons carry a large positive charge, is of similar mass as the neutron but is 1836 times as heavy as an electron.
Radical A radical is a reaction intermediate where a bond is broken and the two parts of the molecule exist carrying a single unshared electron. The radicals are normally destroyed quickly by recombination or they break in another radical and a stable molecule.
Reduction The addition of hydrogen and the removal of oxygen - the oppposite to oxidation, but is now generalised to the inclusion of electrons to a substance by any means.
Salt The ionic product of a reaction between an acid and a base. Water is also formed
Saturated compound An organic compound that does not comprise of carbon-carbon multiple bonds. Examples include ethane and propane.
Solvent A solvent is a substance capable of reataining its physical state whilst forming a homogenous mixture with one or more substances. Some common solvents are listed below:
Surfactant A surface-active agent; one that accumulates at the interface between two liquids and modifies their surface properties. An example would include the sterate ion.
Transmutation The conversion of one element into another by a process taking place in the nucleus.
Ultraviolet light Electromagnetic radiation with a wavelength shorter than that of visible light.
Unsaturated compound An organic compound that contains carbon-carbon multiple bonds. Examples include ethene and propene.
Vitamins The name vitamins is obtained from "vital amines" as it was originally thought that these substances were all amines. This is now known not to be as vitamins have a range of structures. The body requires a small amout of vitamins, but any deficiency leads to metabolic and physical disorders.
Wavelength The distance beween neighbouring peaks of a wave of electromagnetic radiation.