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Chemistry
| Term | Definition |
|---|---|
| Accuracy | How close to the true value a measurement it. |
| Acid | A chemical that is a proton donor and releases H+(aq) in solution. |
| Activation energy | The minimum energy required to start a reaction by breaking the bonds in the reactants. |
| Aim | Identifies the purpose of the investigation. It is a straightforward expression of what the researcher is trying to find out from conducting an investigation. |
| Alcohol | A group of organic compounds where the parent functional group is -OH. |
| Alicyclic hydrocarbon | A hydrocarbon with carbon atoms joined together in a ring structure. |
| Alkali | A chemical that reacts with an acid and is soluble in water releasing hydroxide ions. |
| Alkanes | A homologous series of saturated hydrocarbons. |
| Alkenes | A homologous series of unsaturated hydrocarbons. |
| Amount of substance | The quantity whose unit is the mole. Chemists use "amount of substance" as a means of counting atoms. |
| Amphoteric substances | Substances that can react as both acids and bases. |
| Aliphatic hydrocarbon | A hydrocarbon where carbon atoms are joined together in straight or branched chains. |
| Anhydrous | A substance that contains no water molecules. |
| Anion | A negatively charged ion. |
| Anomalies | Data points that do not fit the overall trend in the data. |
| Anomalous | Results that do not follow the general pattern of the data. |
| Aqueous | A solution in which the solvent is water. It is usually shown in chemical equations by appending (aq) to the relevant formula. |
| Aromatic hydrocarbons | Contain at least one benzene ring. |
| Atom | The smallest object that retains properties of an element. Composed of electrons and a nucleus (containing protons and neutrons). |
| Atomic (proton) number | The number of protons in the nucleus of an atom. |
| Atomic orbital | A region of space where it is likely that you will find electrons. Each orbital can hold up to two electrons, with opposite spins. |
| Atomic radius | A measure of the size of its atoms, usually the mean or typical distance from the nucleus to the boundary of the surrounding cloud of electrons. |
| Atomic structure | Theoretically consists of a positively charged nucleus surrounded by negatively charged electrons revolving in orbits at varying distances from the nucleus. |
| Average bond enthalpy | The mean energy needed for 1 mole of a given type of gaseous bonds to undergo homolytic fission. |
| Avogadro constant | The number of atoms per mole of the carbon-12 isotope. |
| Base | A chemical that can react with acids and its proton acceptor. |
| Biodegradable materials | Are affected by the action of microorganisms and environmental conditions leading to decomposition. |
| Biological catalysts | Catalysts found in nature are called enzymes. Enzymes are of huge importance, for example they help to catalyse reactions in the body. |
| Bioplastics | Materials made from a renewable source that are biodegradable. |
| Bolzmann distribution | The distribution of energies of molecules at a particular temperature, often shown as a graph. |
| Bond angle | The angle that is formed between two adjacent bonds on the same atom. |
| Bonded pair | A pair of electrons that have been shared between two chemically bonded atoms. |
| Bonding region | The space where an electron can be found in a bond. |
| Carbonyls | An organic molecule which contains the C=O functional group. |
| Carboxylic acids | An organic acid containing a carboxyl functional group -COOH. |
| Calorimetry | The quantitative study of energy change in a chemical reaction. |
| Catalyst | A substance that increases the rate of a reaction without being used up during the process. |
| Categoric variables | A qualitative description of a variable. |
| Cation | A positively charged ion. |
| CFCs | Chlorofluorocarbons are a class of organic compounds which contain chlorine and fluorine. They are inert and also non-toxic to humans. |
| Chemical energy | A special form of potential energy stored in chemical bonds. |
| Cis-trans isomerism | A type of E/Z isomerism where two substituent groups attached to each carbon atom of the C=C is the same. |
| Collision theory | A model to help understand and make predictions about how changing temperature, pressure, concentration, surface area of catalyst may change the rate of reaction of a chemical change. |
| Complete combustion | The oxidising of a fuel in a plentiful supply of air. |
| Compound | A substance formed from two or more chemically bonded elements in a fixed ratio, usually shown by a chemical formula. |
| Concentration of a solution | The amount of solute, in mol, dissolved per 1dm3 of a solution. |
| Concordant results | Values that are close to each other and therefore represent reliable quantitative data. |
| Continuous variable | A measured value which could be any number. |
| Control variable | A factor that you must keep constant between experimental runs so that you can compare results. |
| Coordinate bond | A bond formed by a shared pair of electrons that has been provided by one of the bonding atoms only. |
| Covalent bond | A bond formed by a shared pair of electrons between nuclei. |
| Curly arrows | Model the flow of electron pairs during reaction mechanisms. |
| D-orbital | A region within an atom that can hold up to two electrons, with opposite spins. |
| Dative covalent bond | A bond formed by a shared pair of electrons that has been provided by one of the bonding atoms only. |
| Dehydration | A chemical reaction where a water molecule is eliminated from an organic compound. |
| Delocalised electrons | Electrons that are shared between more than two atoms. |
| Delta negative | Slight negative charge. |
| Delta positive | Slight positive charge. |
| Dependent variable | The factor that you observe in an experiment. |
| Diatomic molecules | Molecules composed only of two atoms, of either the same or different elements. |
| Dilute | The process of decreasing the concentration of solute in solution, usually simply by mixing with more solvent. To dilute a solution means to add more solvent without the addition of more solute. |
| Discrete variables | Variables that can only be particular defined numbers. |
| Displacement reaction | A reaction in which a more-reactive element takes the place of a less-reactive element in a compound. |
| Distillation | A technique used to separate miscible liquids or solutions. |
| Dot-and-cross diagrams | Used to model the electrons in chemical bonding. |
| Dot formulae | Gives the ratio between the number of compound molecules and the number of water molecules within the crystalline structure. |
| Dynamic equilibrium | The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and all the chemicals have their concentrations maintained. |
| E/Z isomerism | A type of stereoisomerism that is caused by the restricted rotation around the double bond - two different groups are attached to each carbon atom of the C=C bond. |
| Electrical conductivity | The degree to which a specified material allows charge to be carried. It is calculated as the ratio of the current density in the material to the electrical field which causes the flow of current. |
| Electron configuration | The arrangement of electrons in an atom or ion. |
| Electron shielding | The repulsion between electrons in different inner shells. Shielding reduced the net attraction force from the positive nucleus of the outer-shell electrons. |
| Electronegativity | A measure of the attraction of an electron in a covalent bond. |
| Electrophile | An electron-pair acceptor. |
| Element | A substance that cannot be broken down into simpler substances by chemical means. An element is composed atoms that have the same number of protons in its nucleus as all other atoms of that element. |
| Elimination | An organic chemical reaction in which one reactant forms two products. Usually a small molecule like water is released. |
| Empirical formula | The simplest whole-number ratio of atoms of each element present in a compound. |
| Endothermic | A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings. |
| Enthalpy, H | The heat content that is stored in a chemical system. |
| Enthalpy change of combustion | The energy change that takes place when 1 mole of a substance is completely combustion. |
| Enthalpy change of formation | The energy change that takes place when 1 mole of a compound is formed from its constituent elements in their standard state under standard conditions. |
| Enthalpy change of neutralisation | The energy change associated with the formation of 1 mole of water from a neutralisation reaction, under standard conditions. |
| Enthalpy change of reaction | The energy change associated with a given reaction. |
| Enthalpy change | A pictorial representation showing alternative routes between reactions and products. |
| Enthalpy profile diagram | A diagram of a reaction that allows you to compare the enthalpy of the reactants with the enthalpy of the products. |
| Equilibrium constant | Chemists consider the position of the equilibrium using the equilibrium constant. It gives a measure of where the equilibrium lays, essentially by giving the ratio between products and reactants. |
| Equilibrium law | A law that states for the equilibrium aA + bB + cC + dD. K= cCdD/ aAbB |
| Ester | A functional group of COO found in some organic molecules. |
| Esterification | The chemical reaction which forms an ester. |
| Exothermic | A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings. |
| Experiment | An ordered set of practical steps, which are used to test the hypothesis. |
| Extraneous variable | A factor that is not controlled or measured in an experiment but may introduce error into the results. |
| False positive | A chemical test is when a positive result is produced but not due to the desired product being formed. |
| First ionisation energy | The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions. |
| Fragmentation | The process in mass spectrometry that causes a positive ion to split into pieces, one of which is a positive fragment ion. |
| Functional group | A group of atoms that is responsible for the characteristic chemical reactions of a compound. |
| General formula | The simplest algebraic formula for a homologous series. |
| Giant covalent lattice | A three-dimensional structure of atoms that are all bonded together by strong covalent bonds. |
| Giant ionic lattice | A three-dimensional structure of oppositely charged ions, held together by strong electrostatic forces of attraction (ionic) bonds. |
| Giant metallic lattice | A three-dimensional structure of positive ions and delocalised electrons, bonded together by strong metallic bonds. |
| Global warming | The increases average temperature of the planet and atmosphere, thought to be caused by increases concentrations of carbon dioxide. If unchecked it is thought that global warming will lead to climate change. |
| Gradient | The gradient is the measure of a slope in a graph. For a straight line, choose two points on the graph. Note the change in the y-axis and divide this by the change in the x-axis. |
| Group | A vertical column in the periodic table. Elements in a group have similar chemical properties and their atoms have the same number of outer-shell electrons. |
| Halogenation | An addition reaction where a halogen is added across the C=C group. |
| Haloalkanes | A group of chemical compounds derived from alkanes containing one or more halogens. They are a subset of the general class of halocarbons, although the distinction is not often made. |
| Hess' law | States that the enthalpy change in a chemical reaction is independent of the route it takes. |
| Heterogeneous catalysts | A catalyst used in a reaction which is in the same phase as the reactant. A typical example for this would be a solid catalyst used in liquid reactants, or gaseous reactants passed over a solid catalyst. |
| Heterolytic fission | Happens when each bonding atom receives one electron from the bonded pair; forming two radicals. |
| Homogeneous catalysts | A catalyst used in the reaction which is in the same phase as the reactant. This could include for example in a liquid catalyst that is mixed with liquid reactants. It could also include a gaseous catalyst with gaseous reactants. |
| Homologous series | A series of organic compounds that have the same functional group with successive members differing by CH2. |
| Homolytic fussion | Happens when one bonding atom receives both electrons from the bonding pair. |
| Hydrated | A crystalline compound containing water molecules. |
| Hydration | A reaction where water is a reactant in a chemical reaction. |
| Hydrocarbon | Compounds that contain only hydrogen atoms and carbon atoms. |
| Hydrogen bond | A strong permanent dipole-permanent dipole attraction between an electron-deficient hydrogen atom on one molecule, and a lone pair of electrons on a highly electronegative atom on a different molecule. |
| Hydrogenation | An addition reaction where hydrogen is added across the C=C. |
| Hydrolysis | A chemical reaction in which water is a reactant. There are alkali hydrolysis reactions where -OH- is the reacting species. |
| Hypothesis | A prediction and explanation of the chemistry behind the prediction. |
| Incomplete combustion | Oxidising a fuel in a limited supply of air. |
| Independent variable | The factor that you are interested in changing to see the effect it has on one other factor. |
| Infrared | Refers to the region of the electromagnetic spectrum with wavelengths between 700 nanometres and 300 micrometres. It is the region between red in the visible spectrum and microwaves. |
| Infrared spectroscopy | An analytical technique that utilises a substances behaviour on absorbing infrared radiation and produces a spectrum that can be used to identify certain functional groups, such as the OH group. |
| Intermolecular force | An attractive force between neighbouring molecules or atoms. |
| Ion | A positively or negatively charged atom or (covalently bonded) group of atoms (a molecular ion). |
| Ionic bond | The electrostatic attraction between oppositely charged ions. |
| Ionisation | The process of an atom becoming an ion. |
| Isotopes | Atoms of the same element with different numbers of neutrons. |
| Kilojoules | A measurement of energy, where 1kJ = 1000J. |
| Law of conservation energy | Energy cannot be created or destroyed, only moved from one place to another. |
| Le Chatelier's principle | When a system in dynamic equilibrium is subjected to a change, the position of the equilibrium will shift to minimise the change. |
| Line of best fit | Shows the trend in the plotted points - this could be a straight line, a curve or any "s" shape. |
| London (dispersion) forces | Attractive forces between induced dipoles in neighbouring molecules. |
| Lone pair | An outer-shell pair of electrons that is not involved in chemical bonding. |
| Margin of error | Shows the range that a value lies within. |
| Mass (nucleon) number | The number of particles (protons and neutrons) in the nucleus. |
| Mass spectrometry | An analytical chemistry technique that helps identify the amount and type of chemicals present in a sample by measuring the mass-to-charge ratio and abundance of gas-phase ions. |
| Metallic bonding | The electrostatic attraction between positive metal ions (cations) and delocalised electrons. |
| Meta study and meta-analysis | A type of secondary research. This is using the raw data from a variety of studies and then using it to try to answer the new aim. This is a mathematical approach using statistics and is often used by social scientists. |
| Method | A step-by-step detailed explanation of how to complete an experiment. |
| Molar gas volume | The volume per mole of a gas. The units of molar gas volume are dm^3 mol^-1 . At room temperature and pressure, the molar volume is approximately 24.0. |
| Molar mass, M | The mass per mole of a substance. The units of molar mass are g mol^-1.` |
| Molar volume | The volume per mole of a gas. The units of molar volume are dm^3 mol^-1. At room temperature and pressure, the molar volume is approximately 24.0. |
| Mole | The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope. |
| Molecular formula | Shows the numbers and type of the atoms of each element in a compound. |
| Molecular ion, M+ | The positive ion formed in mass spectrometry when a molecule loses an electron. |
| Molecule | A group of atoms held together by covalent bonds. |
| Monomers | Small molecules that are used to make polymers. |
| Multiple covalent bond | Some non-metallic atoms can share more than one pair of electrons with another atom to form a multiple bond. |
| Neutralisation | The reaction of an acid with a base. |
| Neutron | A particle found in the nucleus of an atom. It is almost identical in mass to a proton, but carries no electrical charge. |
| Nomenclature | The naming system for compounds. |
| Nucleons | Particles found in the nucleus of an atom (protons and neutrons). |
| Nucleophiles | Electron pair-donors. |
| Nucleophilic substitution | A chemical reaction in which an atom or group of atoms is exchanged for a nucleophile. |
| Organic synthesis | A branch of chemistry which designs reactions to make a target molecule. |
| Outline | A summary of the experiment. |
| Oxidation | The loss of electrons, loss of hydrogen, gain of oxygen or an increase in oxidation number. |
| Oxidising agent | A reagent that oxidises (takes electrons from) another species. |
| Ozone layer | An area of high concentration of ozone in the atmosphere. |
| P-orbital | A region within an atom that can hold up to two electrons with opposite spins. |
| Particle model | A simplification of matter which can be used to explain observations and make predictions. |
| Percentage error | A mathematical way of comparing the experimental value with the actual value. |
| Percentage yield | Actual amount, in mol, of product/ theoretical amount, in mol, of product x 100. |
| Periodicity | A regular periodic variation of properties of elements with atomic number and position in the Periodic Table. |
| Permanent dipole | A small charge difference across a bond that results from a difference in the electronegativities of the bonded atoms. |
| Permanent dipole-dipole interaction | A weak attractive force between permanent dipoles and permanent dipoles or induced dipoles in neighbouring polar molecules. |
| Photodegradable | Capable of being decomposed by the action of light, especially sunlight. |
| Pi bonds | Sideways overlap of adjacent p-orbitals above and below the bonding C atoms. |
| Plan | A summary of the experiment that you wish to complete. |
| Polar covalent bond | A covalent bond that has a permanent dipole. |
| Polymers | Macromolecules made from small repeating units. |
| Precipitation reactions | The formation of a solid from a solution during a chemical reaction. Precipitates are often formed when two aqueous solutions are mixed together. |
| Precision | The degree to which repeated values, collected under the same conditions in an experiment, show the same results. |
| Pressure | A measure of the force applied over a unit area. |
| Primary alcohol | Has the functional group attached to a carbon atom with no more than one alkyl group. |
| Primary haloalkane | Has the halogen on the end of the parent chain. |
| Principal quantum number, n | A number representing the relative overall energy of each orbital, which increases with distance from the nucleus. The sets of orbitals with the same n value are referred to as electron shells or energy shells. |
| Product | Substances made/formed in a chemical reactions. |
| Proton | Particle found in a nucleus with a positive charge. The number of these gives the atomic number. |
| Qualitative data | A description of what is being observed. |
| Qualitative test | A simple test where an observation can be used to identify a species. |
| Quantative data | A quantity (number) of what is being observed. |
| Quickfit | A selection of heat resistant glasswear with connectors that can be easily put in a variety of arrangements. |
| Radical | A highly reactive species with one or more unpaired electrons. |
| Radiation | The emission of energy as electromagnetic waves or as moving subatomic particles, especially high0energy particles which cause ionization. |
| Radical substitution | An organic mechanism involving radicals where one or more atoms get exchanged. |
| Rate of reaction | The change in concentration of a reactant or a product in a given time. |
| Reactants | A substance that takes part in and undergoes change during a reaction. |
| Reaction mechanisms | Models which show clearly the movement of electron pairs in a reaction. |
| Recycling | Collecting, sorting and processing of waste for a different use. |
| Redistillation | The purification of a liquid using multiple distillations. |
| Redox reaction | A reaction in which both reduction and oxidation take place. |
| Reducing agent | A reagent that reduces (adds electrons to) another species. |
| Reduction | The gain of electrons, gain of hydrogen, loss of oxygen or a decrease in oxidation number. |
| Reflux | A technique used to stop reaction mixtures boiling away into the air. |
| Relative atomic mass | The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12. |
| Relative isotopic mass | The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12. |
| Reliable | Results that are similar when they are repeated. |
| Repeating unit | A specific arrangement of atoms that occurs in the structure over and over again. |
| Resolution | The smallest change in quantity being measured that can be observed. |
| S-orbital | A spherical shaped region within an atom that can hold up to two electrons with opposite spins. Found at the n=1 level and above. |
| Salt | Any chemical compound formed from an acid when an H+ ion from the acid has been replaced by a metal ion or another positive ion, often a metal or ammonium ion, NH4+. |
| Saturated compounds | Compounds that have only single bonds. |
| Saturated organic chemicals (compounds) | Organic chemicals that have only single covalent bonds. |
| Saturation | The degree or extent to which a species is dissolved or absorbed compared with the maximum possible, usually expressed as a percentage. |
| Scatter graph | A method for expressing quantative data, where the independent variable must be continuous and noted on the x-axis. The dependent variable must also be continuous but displayed on the y-axis. |
| Secondary alcohol | Has the functional group attached to a carbon atom with two alkyl groups. |
| Separating funnel | A piece of equipment used to separate immiscible liquids. |
| Shell | A group of atomic orbitals with the same principal quantum number, n. Also known as a main energy level. |
| Sigma bonds | Made by direct overlap between orbitals on the bonding atoms. |
| Significant figures | The numbers used to represent a quantity that have meaning. |
| Single covalent bonds | Where atoms are bonded by one shared pair of electrons between nuclei. |
| Simple molecular lattice | A three-dimensional structure of molecules held together by weak intermolecular forces. |
| Skeletal formula | A simplified structural formula drawn by removing hydrogen atoms from alkyl chains. |
| Solubility | The property of a solid, liquid, of gaseous chemical substance called solute to dissolve in a solid, liquid or gaseous solvent to form a homogenous solution of the solute in the solvent. |
| Species | Any type of particle that takes place in a chemical reaction. |
| Specific heat capacity | The energy required to raise 1g of a substance by 1K. |
| Standard condition | Standard sets of conditions (temperature and pressure) from experimental measurements established to allow comparisons to be made between different sets of data. This is usually set at 100kPa, 298K and all solutions have a concentration of 1mol dm-3. |
| Standard form | Method for writing very small or very large numbers. Standard form is always written as: A x 10 to the power of n). |
| Standard solution | A solution of known concentration. Standard solutions are normally used in titrations to determine unknown information about another substance. |
| Stereoisomers | Organic compounds with the same molecular formula and structural formula but having different arrangements of atoms in space. |
| Stoichiometry | The molar relationship between the relative quantities of substances taking part in a reaction. |
| Structural formula | Provides the minimum detail to show the arrangement of atoms in a molecule. |
| Structural isomers | Compounds with the same molecular formula but different structural formula. |
| Sub-shell | A group of the same type of atomic orbitals (s, p, d or f) within a shell. An "s" subshell can hold a maximum of 2 electrons, a "p" subshell can hold a maximum of 6 electrons and a "d" subshell can hold a maximum of 10 electrons. |
| Successive ionisation | Values that are a measure of the energy required to remove each electron in turn. |
| Surveys | A type of primary research. It is setting out limits to observe something that is already happening. |
| Sustainability | Chemical processes which minimise the use and generation of hazardous materials. |
| Synthetic polymers | Human-made polymers. |
| Table | A clear and structured way of recording information about an experiment. |
| Tertiary alcohol | Has the functional group attached to a carbon atom with three alkyl groups. |
| Thermodynamics | A branch of physical chemistry concerned with changes in the energy of chemical systems and surroundings. |
| Titrations | The slow addition of one solution of a known concentration (called a titrant) to a known volume of another solution of unknown concentration until the reaction reaches an end point, which is often indicated by a colour change. |
| Unsaturated organic chemicals (compounds) | Organic chemicals that contain at least one carbon-carbon double covalent bond. |
| Valid experiment | Provides information to test the aim of the experiment. |
| Van der Waals' forces | A type of intermolecular bonding that includes permanent dipole-dipole bonding and induced dipole-dipole interactions (London forces). |
| Variables | Factors that can affect the outcome of an experiment. |
| Volatility | The tendency of a substance to vaporize. |
| Volume | The quantity of three-dimensional space occupied by a liquid, solid, or gas. |
| Water of crystallisation | Water molecules that form an essential part of the crystalline structure of a compound. |
| Weighing by difference | A method used to accurately weigh the amount of material transferred. The mass of a container before and after transferring the material is taken and the difference between these values is the mass of material transferred. |
| Yield | The amount of product obtained in a chemical reaction. |
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