Chemistry Encyclopedia

Chemistry Encyclopedia

If you would like to prepare for school subjects or simply increase your general knowledge, then enjoy our chemistry encyclopedia. We tried to focus only on very important terms and definitions. We also kept our terminology very brief so that you absorb the concept more quickly and easily.

Chemistry Glossary (Page 1)


NITRILE: A carbon compound containing a carbon-nitrogen triple bond. An example is acetonitrile, a common organic solvent- Nitro- The -NO2 functional group. You may have heard of trinitrotoluene (TNT) - here's a picturenobel Prize- An award given for really good scientific work, usually once all the dust has settled and the people who did are decently old and respectable.
ABSORPTION: Not to be confused with adsorption, absorption is one substance is taken up into the interior of another - adsorption with a 'd' is entirely a surface effect. Examples are the swelling of a poly(acrylamide) polymer with aqueous solution (in a disposable nappy) or the dissolution of carbon dioxide in seawater (one of the possible antidotes to global warming that crops up in models of world climate.
ACCELERATION: Measure of how fast velocity is changing, so we can think of it as the change in velocity over change in time. The most common use of acceleration is acceleration due to gravity, which can also appear as the gravitational constant (9.8 m/s2).
ACETALDEHYDE: Oops, I should have used the systematic name, ethanal! This is a good example of a case where the IUPAC system may be logical, but can easily engender no end of confusion.
ACID: There are three definitions - Arrhenius, Bronsted, and Lewis Acids. In the Lewis conception, which is the most general and useful, an acid is essentially any compound that needs electrons, and a base is basically any compound that wants to give them away. .
ACID ANHYDRIDE: Take two carboxylic acid molecules - for example, salicylic acid - and remove water to give a molecule containing a -(C=O)-O-(C=O)- link - this molecule will be an acid anhydride.
ACID CHLORIDE: Take a carboxylic acid and replace the OH group with a Chlorine atom. What you now have is an acid chloride. Acid chlorides react readily with water to regenerate carboxylic acid + hcl. Acidic- Forming or containing an acid.
ACIDIC: Describes a solution with a high concentration of H+ ions.
ACRYLONITRILE: A common monomer used in free-radical polymerisation. Acrylonitrile is one of the more toxic monomers, and is a proven carcinogen; one of its main applications is in the production of carbon fibres.
ACTIVE CENTRE: In chain-growth polymerisation, the highly-reactive spot on the growing polymer chain where new monomer is added. The four most common types are a free-radical (atom with an unpaired electron), carbanion (carbon-centred negative ion), carbocation (carbon-centred positive ion) or a metal complex (as in Ziegler-Natta polymerisation).
ADDITION POLYMERISATION: Also known as chain-growth polymerisation. The mechanism in which large numbers of usually identical small molecules are joined together to rapidly form a single large molecule. This involves the addition of reactive centre (anion, cation, or unpaired electron) to a multiple bond to form a new bond and a new reactive centre - which reacts with another multiple bond, et cetera... The finished chain then hangs around without reacting while more of the starting material reacts to form new polymer chains.
ADSORPTION: Not to be confused with absorption, adsorption is the build up of a molecule at a surface (such as an oil/water interface). Adsorption generally occurs because different parts of a molecule have an affinity for the two different phase on either side of the interface.
AKUBRAS: We thought we would put this in because we have met people from New Zealand who didn't know what they were and understand that there are a few New Zealanders in New South Wales. Akubras are a kind of you beaut hat that all real Ostrayans (e.g., Greg Norman) wear.
ALCOHOL: Any chemical compound where the hydroxy functional group -O-H is bound to an carbon skeleton. You are probably most familiar with the diols (compounds with two hydroxy groups), which are used in the manufacture of polyesters, and the phenols, where an hydroxy group is bound to an arene.
ALDEHYDE: Any chemical compound containing the functional group -C(O)H. Acrolein, the simplest aldehyde that is also a monomer capable of undergoing addition polymerisation, is responsible for the distinctive smell of burning fat. Here is a picture-Alfred Nobel- A Swedish inventor, businessman and famous posthumous philanthropist (1833-1896). He developed the mercury percussion detonator (1863) and numerous other advances in explosives technology to make blasting safer and easier. He made a lot of money, which he left in his will to provide prizes for people whose work had been of great benefit to humanity, and economists. See Nobel Prize.
ALKALINE: Forming or containing an alkali, and by extension, any base. Strictly speaking, an alkali is the hydroxide or carbonate salt of an element in the first two columns of the periodic table (those unstable alkali and alkaline earth metals things).
ALKANE: Carbon compound containing only carbon and hydrogen, and single bonds only.
ALKANOIC ACID: The proper IUPAC term for what we typically call carboxylic acids.
ALKENE: Carbon compound containing carbon and hydrogen incorporating one or more double bonds.
ALKYL HALIDE: A carbon compound containing a covalent bond between a halogen (fluorine, chlorine, bromine, iodine) and an alkane.
ALKYNE: Carbon compound containing carbon and hydrogen incorporating one or more triple bondsamide- Any carbon compound containing the functional group -C(O)NH. Acrylamide, CH2=CH-C(O)NH, is one of the nastiest pieces of work you could hope to come across, but poly(acrylamide) is an innocuous compound found in disposable nappies. Get a disposable nappy and tear it open; you will find cottony padding stuff, and a gritty substance - this grit is small particles of cross-linked poly(acrylamide). Amine- Any carbon compound containing the nitorgen bound only to carbon or hydrogen. The functional group for a primary amine is -NH2, for a secondary amine -NH-, and for a tertiary amine a nitrogen bound the three carbon chains. Amino acids are carbon compounds containing both amine and carboxylic acid groups - e.g., glycine, NH2-CH2-COOH. (Biochemists give this compound the symbol (G))Amino acid- A carbon compound containing both an amine (NH2) and an carboxylic acid (-C(O)-OH) functional group. Amino acids are the building blocks of proteins, which can be considered a special case of condensation polymers. Twenty main amino acids are responsible for most of the incredible variation in proteins, and these have been given one letter symbols (G, Q, V, etc.) By biochemists. An example is glycine, NH2-CH2-COOH. (Biochemists give this compound the symbol (G))"Amphiphilic- From the greek meaning 'both' (something like amphi) and 'lover' (something like philos). An amphiphile is a molecule that has a strong attraction towards both polar solvents (like a hydrophile) and non-polar solvents (like a hydrophobe) and will end up concentrated at the interface between the two.
ANION: Ions with a negative charge.
ANIONIC: A negatively charged chemical species, like the hydroxide OH-, carbonate CO32-, or sulphate SO42-, is called an anion. In an electrochemical cell, an anion will move towards the anode to lose its extra electron and generate a current.
ANODE: The electrode where electrons are lost (oxidized) in redox reactions.
ANTHROPOGENIC: A fancy way of saying "man-made" that hides its lack of political correctness in greek. Think of 'anthropoid' and 'genesis'.
AREA: Measures the size of a surface using length measurements in two dimensions.
ARENE: Any carbon compound containing a six membered ring of carbons, each of which forms only one chemical bond outside of the ring. This is called a phenyl ring, and though it looks like it has alternating single and double bonds, all the bonds are actually the same. Benzene is the simplest arene; other examples are toluene, fulvic acid, and trinitrotoluene - Australian Research Council- Australia's peak science funding body. The ARC is responsible for running the competitive grant process which is used to determine which proposed research is funded by the Commonwealth government. The ARC's Research Centres Programme established and continues to support the Key Centre for Polymer Colloids.
ASSOCIATIVITY: A property in math which states that-(A+B)+C=A+(B+C) and (A*B)*C=A*(B*C).
ATMOSPHERES: Common units for measuring pressure.
ATOM: The smallest object that retains properties of an element. Composed of electrons and a nucleus (containing protons and neutrons).
ATOMIC NUMBER: Number of protons in an element.
AVOGADRO'S NUMBER: Number representing the number of molecules in one (1) mole-6.022 * 1023.
BACTERIA: Single-celled organisms that probably provide the bulk of the biomass on our planet. There are more bacterial cells within your body than human cells. One of the most interesting things about bacteria is that our macroscopic concepts of 'species' are rather inappropriate - genetic material can be swapped from one 'species' to another with disturbing ease, leading some scientists to call all bacteria a single 'superorganism'. The fantastic durability and longevity of bacteria (some concentrate plutonium inside themselves and happily live inside high level nuclear waste facilities, while others are believed to have survived for tens of millions of years in rock formations) have led some other scientists to speculate they are adapted to life in deep space and are continually raining down on us from above.
BASE: Substance which gives off hydroxide ions (OH-) in solution.
BASIC: Having the characteristics of a base.
BENZOYL PEROXIDE: A common initiator used to start chain growth polymerisation. It undergoes a decomposition reaction at the peroxide (O-O) bond. Here is a picture-Biocompatible- A material may be regarded as biocompatible if it may be put into living organisms without rejection or detrimental effects. Materials may also be considered to be bioinert if they do not interact with the body at all (like titanium knee implants).
BIODEGRADABLE: Capable of being eaten or otherwise decomposed by some kind of living creature. Bacteria and fungi are the main culprits; we usually use the word edible for things that can be eaten by animals. It is important to consider the timescale involved - paper is biodegradable, but can kick around for a very long time before succumbing. Most synthetic polymers are not particularly biodegradable (poly(acrylamide) is a rare example of one that is readily degraded), but many are susceptible to breakdown by ultraviolet radiation from the sun and will crumble away in about the same time as an equivalent sheet of paper.
BIOPOLYMER: A polymer produced by a living plant, animal fungus, bacterium, or other biological entity.
BIOSYNTHESIS: The production of a chemical by bacteria or other living organisms.
BOHR'S ATOM: Bohr made significant contributions to the atom. He understood the line spectra- the reason why only certain wavelengths are emitted when atoms jump down levels.
BOILING POINT: The temperature at which the pressure exerted by molecules leaving a liquid equals the pressure exerted by the molecules in the air above it. A free-for-all of molecules leaving the liquid then ensues. In a solution, the boiling point will be increased by a number that depends on the number of particles in solution- delta(T) = Kb × (number of solute molecules per litre)- where delta(T) is the rise in the boiling point and Kb is called the 'ebullioscopic constant' and varies from one solvent to another.
BREAKFAST CEREAL: A possible future application for synthetic polymers... Using polyester instead of wheat could give a product with a much longer shelf life, and you probably couldn't tell the difference once it was covered with sugar and artificial colouring.
BUFFER SOLUTIONS: Solutions that resist changes in their ph, even when small amounts of acid or base are added.
BUTADIENE: Common monomer in chain-growth polymerisation; an important constituent of ABS rubber. Here is a picture- Calorimetry- Calorimetry is a technique for measuring the heat generated or lost in a chemical reaction. The reaction is carried out in such a way that as much as possible of the heat change is transferred to another material, raising its temperature. The heat generated can then be calculated from the amount of the material heated and its specific heat.
CARBANION: An anion where the negative charge is localised on a carbon atom is imaginatively called a carbanion. The best way to generate a carbanion is to remove a H+ ion from a hydrocarbon. Since carbanions are conjugate bases to very very very weak acids indeed, they are fiendishly reactive bases.
CARBENIUM: If a negatively charged hyride (H-) ion is removed from a hydrocarbon, what is left is a positively charged carbenium ion, a form of carbocation.
CARBOCATION: A positively-charged chemical species where the positive charge is localised on a carbon atom. Both carbenium ions (which have three bonds to a positively charged carbon) and carbonium ions (which may have five or more bonds to a positively charged carbon) are examples of carbocations.
CARBONIUM: If there are five or more bonds to a single carbon atoms, it will be short of electrons and have a positive charge - this species is called a carbonium ion, a form of carbocation. The easiest way to make one is to add a hydrogen ion (H+).
CARBOXYLATE GROUP: When a carboxylic (alkanoic) acid is deprotonated (i.e., loses a H+ ion) what is left is a negatively-charged carboxylate ion.
CARBOXYLIC ACID: Any carbon compound containing the functional group -C(O)OH. Formic acid (HCOOH) gives the distinctive smell of crushed ants, while acetic acid (CH3COOH) gives VB its distinctive odour and taste.
CAROTHERS: Wallace Hume Carrothers (1896-1937) carried out the key early experiments that led to commercial polyesters, nylons, and neoprene while working for the dupont corporation and almost single-handedly created the polymer industry in the United States. His amazing scientific achievements did not bring him happiness, and he tragically committed suicide by taking cyanide.
CATALYST: Compound that accelerates the rate of a chemical reaction, and is not itself consumed in the reaction.
CATALYTIC CRACKING: A method of cracking that uses a catalyst to convert hydrocarbons to positively charged carbocations, which then break down into smaller molecules. This can be carried out at much lower temperatures than thermal cracking - still hot, 500-600°C as compared to around 700°C, but that difference adds up to a lot of $$$.
CATHODE: Electrode where electrons are gained (reduction) in redox reactions.
CATIONIC CATION: A positively charged chemical species, like the ammonium NH4+ and scandium Sc4+ ions, is called a cation. In an electrochemical cell, a cation will move towards the cathode to gain an electron to remove its excess positive charge.
CATIONS: Ion with a positive charge.
CAUSTIC SODA: When used in industrial processes, sodium hydroxide is often known as caustic soda.
CEILING TEMPERATURE: Above a certain temperature, monomers can no longer be persuaded to form polymers by chain polymerisation. This occurs when the loss in entropy arising from joining many molecules into one outweighs the energetic benefit of converting double bonds to single bonds. A chain-growth polymer raised above the ceiling temperature will degrade, or depolymerise.
CELLULASE: No, not a misspelling of cellulose... Cellulase is an enzyme capable of depolymerising cellulose to form glucose. Chemists like these sort of words - see if your teacher can tell you the definitions of 'filtrate' and 'filtrant' without having to think about it for a couple of minutes... And if they get that one right, test them out on 'carbenium' and 'carbonium' ions!Cellulose- Cellulose is a large component of the biomass of plants and the main source of food energy for the world's termite population. It can be considered to be a condensation polymer of glucose, like starch, but the links between the glucose monomers are slightly different.
CENTRAL ATOM: In a Lewis structure, usually the atom that is the least electronegative.
CHAIN REACTION: A really dodgy film starring Keanu Reeves. Also, a mechanism that has no reason to stop, since the product is just as reactive as the reactants.
CHARGE: Describes an object's ability to repel or attract other objects. Protons have positive charges while electrons have negative charges. Like charges repel each other while opposite charges, such as protons and electrons, attract one another.
CHEMICAL CHANGES: Processes or events that have altered the fundamental structure of something.
CHEMICAL ENGINEERS: People who carry out chemical reactions in ten-ton reactors instead of test tubes. Real chemists tend to assume that chemical engineers just mix up reactions that other people have developed in big buckets, but i've looked at some of the books they have to read and they're full of hairy maths, so some parts of what they do must be kind of tricky. Their main job is actually to design the buckets, how they're stirred, and how things get in and out of them, so that they don't explode, shower the surrounding countryside with toxic waste, or otherwise cost the chemical company too much money. See Industrial Chemist.
CHEMICAL EQUATION: An expression of a fundamental change in the chemical substances.
CLOSURE: A mathematical term which says that if you operated on any two real numbers A and B with +, -, * or /, you get a real number.
COAGULATION: Coagulation and coalescence are both words that are used to describe what happens when small particles in a dispersion combine together to form large ones. One example is what happens to milk (a nice disperse emulsion) if it is leftat the back of the fridge too long. Coagulation is used when the particles that are combining are more or less solids, and coalescnce is usually restricted to droplets of liquid.
COHESION: Cohesion just means "sticking together" and cohesive forces are the forces that enable something to stick to itself. For example, if you glue two objects together and then break them apart, a cohesive failure is where the glue itself breaks, as opposed to an adhesive failure where the break is at the join between the glue and one of the objects.
COLLIGATIVE PROPERTIES: Properties of a solution that depend only on the number of particles dissolved in it, not the properties of the particles themselves. The main colligative properties addressed at this web site are boiling point elevation and freezing point depression.
COLLOID: If the size of a particle is of the order 10 nm to 1 micron (10-8 to 10-6 metres), then a mixture of these particles with a continuous phase (e. G., tiny particles of dust in air or polymer in water) will have properties that are intermediate between those of a true solution and a mixture of largish particles in a substance. Three key things to remember about colloids are- About the same size as a wavelength of light. Largely unaffected by gravity. A large proportion of the molecules in a colloidal particle are at or near the particle surfacecomonomer- A monomer that is polymerised along with one or more other monomers to make a copolymer. All the different comonomers used in a copolymerisation are incorporated into each chain.
COMBUSTION: When substances combine with oxygen and release energy.
COMMUTATIVITY: A math property which states-A+B=B+A and A*B=B*A.
COMPOUND: Two or more atoms joined together chemically, with covalent or ionic bonds.
CONCENTRATION: The amount of substance in a specified space.
CONDENSATION POLYMERISATION: Also known as Step-Growth Polymerisation. A way of makiing polymers in which every polymer chain grows continuously through the course of the reaction, remaining quite small until almost all the monomer has reacted.
CONJUGATE ACID: A substance which can lose a H+ ion to form a base.
CONJUGATE BASE: A substance which can gain a H+ ion to form an acid.
COPOLYMER: A polymer that is made up of more than one monomer unit. A copolymer has each of its comonomers in every chain. There are a number of different types of copolymer which describe the nature of the arrangement of the comonomers within the polymer chain. Corrosion inhibition- Corrosion can be defined as the unwanted production of a salt from a metal. Adding acid or oxygen are good ways to do this. The main ways of slowing corrosion down (inhibition) are by providing an impermeable coating to stop the chemical reaction from occuring in the first place, or by providing a more easily attacked metal which will be consumed first (a 'sacrificial anode')Coulomb- An Amp(ere) of current is what you get one one Coulomb worth of electric charge flows past a point in one second - i.e., 1 A = 1 C/s. One mole of electrons has a charge of 96 500 C, which is called a Farad.
COVALENT BONDS: When two atoms share at least one pair of electrons.
CRACKING: The process in which large molecules found in crude oil are broken down into smaller molecules. See Catalytic Cracking and Thermal crackingcrude Oil- Tarry goop consisting of mixed carbon compounds with a highly variable composition. Not much to look at, but the basis for the chemical industry, modern transport, and many shopping sprees at Harrods.
CRYSTAL: A large number of objects that are all the same size and shape and are attracted to one another will tend to form repeating three-dimensional structures, instead of lying about randomly. A more complicated crystal will be formed if more than one kind of object is present. You are probably most familiar with crystals of simple covalent solids (like sugar) or ionic solids(like table salt), where the attractive forces between perfectly ordinary molecules and ions line up in an orderly fashion to give structure that we can actually see on the macroscopic scale. It is possible to form crystals even of proteins with molecualr weights approaching a million, as each molecule of a protein will have the same molecular weight and three-dimensional shape, and we have all seen 'crystals' of oranges stacked in fruit shops.
DAUGHTER ISOTOPE: In a nuclear equation the compound remaining after the parent isotope (the original isotope) has undergone decay. A compound undergoing decay, such as alpha decay, will break into an alpha particle and a daughter isotope.
DECAY: Change of an element into a different element, usually with some other particle(s) and energy emitted.
DECIMAL: The number of digits to the right of the decimal point in a number.
DENSE: A compact substance or a substance with a high density.
DENSITY: To find the density of an object, you measure its mass and its volume, then divide the mass by the volume, giving a density measured in g/cm3 or kg/dm-3. Since all atoms are about the same size, the densest materials are metals like osmium and gold, which are elements with heavy nuclei, and the least dense are the very first elements in the periodic table, the gases hydrogen and helium.
DEPOLYMERISATION: The chemical reaction which results in a polymer chain being broken up into monomer units. For most polymers made by addition polymerisation, this is done by heating the polymer above its ceiling temperature in the absence of oxygen. Some polymers, like styrene and vinyl chloride, will be difficult to depolymerise because the bonds between the side-groups (the phenyl ring and chlorine in these examples) are weaker than the C-C bonds between ex-monomers, and the polymer will degrade into different species than the starting materials. Other polymers, such as those made by step growth polymerisation may be more easily depolymerised by undoing the condensation or elimination reaction that caused the monomer units to join. In the lab, this can often be done using a strong acid in harsh conditions, although industrially, there are other tricks that polymer scientists can play.
DEPROPAGATION: The reaction in which small alkenes are generated from the decompostion of a large alkane radical. This reaction is important in Thermal Cracking, and is responsible for the ceiling temperature, which prohibits chain polymerisation above a certain temperature.
DETERGENCY: Detergency is the property of surfactants that allows them to clean things for us. The surfactants accumulate on the oil/water interface so that when we scrub the oily stain to break it up, the oil drops do not coaleasce.
DETERGENT: A detergent is a type of surfactant. Essentially, a detergent is any surfactant that is not a soap.
DIBASIC: An acid that has two acidic hydrogen atoms that can react with a base is dibasic. An example is the amino acid aspartic acid, which contains two carboxylic acid groups with different reactivities. Dimer- A dimer is two molecules (of the same type) bonded together. (just as monomer is one (mono) unit (mer) a dimer is two units).
DIPOLE: If one part of a molecule is more attractive to electrons than another part, it will have a permanent uneven distribution of charge - i.e., one end will be slightly positive and one will be slightly negative. There will be an attraction between two molecules of this substance, since they will turn so that the positive end of one is facing the negative end of the other.
DIPOLE-DIPOLE FORCES: Intermolecular forces that exist between polar molecules. Active only when the molecules are close together. The strengths of intermolecular attractions increase when polarity increases.
DISACCHARIDE: Just as there are monomers, dimers, trimers, oligomers, and polymers, indicating one, two, three, several, and many identical units joined together in a molecule, the combinations of saccharides (aka sugars) are known as mono-, di-, tri-, oligo- and polysaccharides. An example of a disaccharide is sucrose, composed of the simple sugars glucose and fructose joined by an ether linkage. An example of a polysaccharide is chitin, a nitrogen-containing polymer of modified glucose units that makes up the exoskeleton of insects.
DISPERSION: Two substances mixed together such that one is not dissolved in the other. For example, milk, a dispersion of globules of fat in water; latex paint, a dispersion of polymer particles in water; smoke, a dispersion of carbon particles in air.
DISPERSION FORCES: Since electrons move around, even a molecule with no permanent separation of charge will have negative and positively charged bits from one instant to another. These imperfections generate an overall attractive force even between molecules as unreactive as N2. Since this explanation is already too complicated for anyone to understand, I may as well go on to say that they are called Dispersion Forces because they are related to a quantity called the dispersion of a substance, which is the rate of change in refractive index with frequency of transmitted radiation. You can also call them London Forces, after Fritz London (1900-1954).
DISSOCIATION: Breaking down of a compound into its components to form ions from an ionic substance.
DISTILLATION: Separation of two liquid compounds by boiling point. For example, a mixture of two hydrocarbons can be heated so that the lower molecular weight hydrocarbon evaporates - if the vapour is not allowed to escape, but taken around the corner and cooled down, it can be extracted as a pure liquid.
DISTRIBUTIVITY: A math property which states-A*(B+C)=(A*B)+(A*C).
DODGY EXAMPLE: Imagine you have a certain number of Queenslanders, each representing molecules of the same reactant in a chemical reaction. You apply metaphorical kinetic energy (give them car keys) and tell them that they can have $10000 dollars if they meet you at a certain address in North Sydney. There is a strong incentive for them to meet you there (the reaction Queensland -> North Sydeny) is thermodynamically favoured) - but, chances are they will get sucked through the Harbour Tunnel and Eastern Distributor to Botany instead (the reaction Queensland -> Botany is kinetically favoured). If you stop the reaction while they are all in Botany, you will obtain the kinetic product, but if you let them keep the car keys you should end up with the thermodynamic product eventually. At a certain stage in the reaction, you will have a mixture of the kinetic and thermodynamic products.

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