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226 Cards in this Set
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absorption (med.)
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The movement and uptake of substances into cells, and across tissues such as skin or intestines, by osmosis and diffusion.
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Acid
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A substance which contains hydrogen that can be replaced by a metal, liberates carbon dioxide from carbonates, and in solutions turns litmus red; a substance which can donate protons.
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Addition (IGCSE)
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A reaction in which two or more atoms are joined to a compound without elimination
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Alkali
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A substance which will neutralize an acid to form a salt and water only; a substance which dissolves in water to produce hydroxide ions (OH-); a soluble base; a proton acceptor
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Alkali metals
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The elements of group 1 in the Periodic Table (litium, sodium, potassium, rubidium, and caesium)
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Alkaline earth metals
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The elements of group 2 in the Periodic Table (beryllium, magnesium, calcium, strontium, barium, and radium).
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Alloy
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A mixture or combination of two or more metals
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Allotropy
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The existence of an element in more than one form in the same state. The different forms are called allotropes and differ in their structure, for example, diamond, graphite and buckminster-fullerenes are all allotropes of carbon.
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Amphoteric
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A substance capable of acting both as an acid and as a base
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Analysis
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The determination of the composition and/or structure of a substance or mixture, often by controlled decompostion or instrumental methods
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Anhydrous
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Without water; for example, anhydrous copper(II) sulphate
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Anion
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A negatively charged ion which is attracted towards the anode in electrolysis
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Anode
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The positive electrode
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Atom
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The smallest part of an element which can take part in a chemical reaction
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Atomic Weight
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Obsolete, but see relative atomic mass below
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Atomicity
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The number of atoms in a molecule; for example, the atomicity of hydrogen, H2, is 2.
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Avogadro Constant (IGCSE)
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Is approximately 6 x 1023 mol-1, the number of atoms per mole of 12C
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Base
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A substance which reacts with an acid to form a salt and water only; a proton acceptor, for example, OH-, NH3.
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Beta-particle
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An electron given off by the nucleus of a radioactive substance
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Boiling
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The change of state from liquid to vapor at the boiling point
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Boiling Temperature (point)
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The temperature at which the vapor pressure of the liquid is equal to the external pressure - usually quoted for atmospheric pressure.
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Catalyst (IGCSE)
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A substance which changes the rate of a reaction, but is itself unchanged in mass at the end of the reaction.
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Cathode
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The negative electrode
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Chromatography
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A method of separating substances; as they move through a stationary phase, the components of the mixture are differentially adsorbed and so move at different rates, producing a chromatogram. Especially useful for separating and identifying the products of hydrolysis of carbohydrates and proteins
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Combustion
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Burning, usually in air
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Compound
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A compound is formed when two or more elements are chemically combined in definite proportions by mass.
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Condensation
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The change of state from vapor to liquid; often deliberately induced by cooling, as in a Liebig condenser.
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Cracking (IGCSE)
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The decomposition of a chemical substance by heat; this usually refers to mineral oils of high boiling temperature being broken down into more volatile components of lower molar mass; unsaturated hydrocarbons are produced in this process.
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Crystal
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A solid whose atoms are arranged in a definite pattern, giving rise to an external geometric form.
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Crystallisation
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The process whereby crystals are obtained, either from solution or the molten state, usually by cooling.
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Diffusion
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The process whereby particles move freely through both gases and solutions to produce a uniform or homogeneous system
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Distillation
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The process which occurs when a liquid is converted to a vapor by heating, and then the vapor is recondensed to a liquid; it is used for the separation or purification of liquids. The product is called the distillate.
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Electrode
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A conductor by which an electric current enters or leaves an electrolyte during electrolysis.
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Electrolysis
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This occurs when a substance, either in solution or the molten state, is decomposed by the passage of an electric current.
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Electrolyte
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The substance which undergoes electrolysis, either in solution or the molten state, for example, copper(II) sulphate solution, or molten lead(II) bromide
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Electron
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A sub-atomic elementary particle, having unit negative charge and a mass approximately 1/1840 of a proton; it also exhibits wave properties.
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Endothermic
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A process during which thermal energy is absorbed
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Equilibrium (IGCSE)
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A reaction in which both reactants and products are present and are being dynamically converted into one another.
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Evaporation
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The change of state from liquid to vapor below the boiling point; it occurs from the surface of the liquid.
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Exothermic
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This describes a process which gives out thermal energy
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Fermentation
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The process whereby complex carbon compounds (mostly carbohydrates) are converted to simpler products by enzymes present in micro-organisms
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Filtration
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The process of separating solids from liquids by passing them through a porous material (in the laboratory usually filter paper); the liquid which passes through is called the filtrate; the solid left behind is called the residue
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Fractional distillation (IGCSE)
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The separation of several liquids which have different boiling points, by collecting the distillates (fractions) at different temperatures
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Freezing
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Change of state from liquid to solid at a constant temperature
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Homologous series (IGCSE)
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A set of organic compounds with similar chemical properties and a regular gradation of physical properties and for which a general formula can be written.
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Hydrocarbon
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A compound of carbon and hydrogen only
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Ion
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An electrically charged particle formed from an atom or group of atoms by loss or gain of electrons, for example Na+, Pb2+, Cl-, SO42-
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Indicator
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A substance which exhibits different colors in acidic or alkaline conditions, for example litmus.
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Isomer
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One of two or more substances with the same molecular formulae but different structural formulae.
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Melting
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The change of state from solid to liquid
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Melting temperature (point)
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The temperature at which the solid and liquid phase of a substance are in equilibrium at a given pressure.
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Mineral
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A naturally occurring inorganic substance with a characteristic chemical compostion and usually a definite crystal form
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Mole (IGCSE)
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The unit of amount of substance. One mole is that amount of substance which contains as many specified elementary particles as there are atoms in 0.012kg of the isotope 12C
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Molecule
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The smallest part of a substance which can exist independently and still retain the properties of that substance. For example, Cl2, HCl, H2O, C2H5OH
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Neutralisation
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The addition of an acid to an alkali, or vice versa, until neither is in excess and the solution is neutral.
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Neutron
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A sub-atomic elementary particle, having the same mass as a proton but no charge
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Ore
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A solid, naturally-occurring mineral from which metals or other valuable constituents can be obtained, usually by chemical treatment
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Oxidation
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The addition of oxygen or the removal of hydrogen. An increase in the oxidation state of an element is oxidation. Oxidation is loss of one or more electrons.
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pH scale
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A measure of the hydrogen ion concentration in water, hence of the acidity or alkalinity of a solution. A neutral solution has a pH value of 7; acidic solutions have pH values less than 7; alkaline solutions have pH values greater than 7.
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Polymerisation
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The process in which two or more molecules of the same compound combine to form larger molecules which have the same empirical formula but a higher molar mass.
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Precipitate
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An insoluble substance which separates from solution during a chemical reaction.
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Proton (IGCSE)
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A sub-atomic elementary particle, with unit positive charge and unit mass, expressed in relative atomic mass units.(The actual unit is approximately 166 x 10-24)
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Proton number
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The number of protons in the nucleus of an element
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Reduction
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The removal of oxygen or the addition of hydrogen. A decrease in the oxidation state of an element is reduction. Reduction is the gain of one or more electrons.
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Redox reaction
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A reaction where reduction and oxidation are occurring
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Refine
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To purify; especially applied to crude oil
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Relative atomic mass (IGCSE)
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The ratio of the average mass per atom of an element relative to 1/12 the mass of an atom of 12C.
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Relative molecular mass (IGCSE)
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The sum of the relative atomic masses of the elements in a compound
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Reversible reaction (IGCSE)
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A reaction which can be made to proceed either forwards or backwards under suitable conditions; a reaction in which both products and reactants are present at equilibrium.
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Salt
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The product obtained when part or all of the hydrogen of an acid is replaced by a metal (or the ammonium group). An ionic solid formed from positive ions, other than H+ ions, and negative ions, other than OH- and O2- ions; for example NaCl, CuSO4
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Saturated compound
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An organic compound containing no carbon-carbon multiple bonds
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Saturated solution (IGCSE)
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A solution which remains in equilibrium with undissolved solute
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Smelting
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The extraction of a metal from its ore, using heat, normally by reduction with carbon or carbon monoxide.
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Solute
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A solute is a substance which dissolves in a solvent to form a solution
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State symbols
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These are included in the equation for a reaction to indicate the physical state of the substances. They are as follows: (g), gaseous; (l), liquid; (s), solid; (aq), aqueous - dissolved in water.
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Sublimation
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The change from solid to gas and back to solid without passing through the liquid state.
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Synthesis
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Putting together'. The formation of a substance from simpler substances. The adjective synthetic is often applied to substances which are artificially produced and not obtained from naturally occurring material.
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Unsaturated
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An organic compound containing one or more carbon-carbon multiple bonds
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activation energy
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The minimum energy required for a collision to be able to result in a reaction
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addition
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a reaction in which two or more atoms are joined to a compound without elimination
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addition polymerisation
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the process by whcih two or more molecules of a monomer combine by an addition reaction to form larger molecules of a new compound which has the same empirical formula but a larger molar mass
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addition reaction
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a reaction in which one molecule adds onto another to give a single product
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adrenaline
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A hormone produced by the adrenal gland in mammals, in response to low blood glucose level, exercise and stress. Adrenaline causes a breakdown of the carbohydrate food store glycogen to glucose and increases its uptake by cells. It also causes vasodilation of small arteries and increases heart rate.
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alveoli
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The balloon like cavity at the end of the bronchioles (the tiny tubes in the lungs). Each alveolus is surrounded by blood vessels to absorb the oxygen from the air and return carbon dioxide to the air. Each lung contains about 300 million alveoli.
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anaesthetic
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A drug or agent that causes loss of feeling or sensation of pain.
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antagonist
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A term used to describe a drug that has an affinity for a specific cell receptors; agonists stimulate a response in the same way as the substance produced by the body which normally fits that receptor site, so increasing response.
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antibiotic
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A substance which inhibits the growth or destroys bacteria. Louis Pasteur and Paul Erlich were pioneering scientists in this field.
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antibody
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A protein molecule which helps to defend the body against disease. Antibodies are produced mostly by white blood cells in response to an antigen.
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antifungal
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A term used to describe a drug which destroys or suppresses the growth of fungi, often to used to treat fungal infections.
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antigen
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A process which gives immune resistance to a particular disease. It involves exposing the human or animal to the antigen in order to raise antibodies and provide an immune memory in that organism. The antigen is made harmless before exposure.
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antigen
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A substance which is foreign to the body which initiates an immune response. Most antigens are proteins, found on the surfaces of bacteria or viruses.
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antiseptic
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A substance that inhibits the growth and development of microorganisms without necessarily killing them.
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antiviral
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A drug which helps cells to defend themselves against viruses, by reducing DNA synthesis or by making cells more resistant to virus particle, or by surpressing their replication within the host cell.
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arteries
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Blood vessels that carry blood from the heart to the muscles and organs of the body. The blood is pressurised so they have thisck walls. The blood in the arteris is oxygenated and red (except for the pulmonary artery that takes blood from the heart to the lungs to pick up oxygen).
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Aufbau Principle
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The construction of the The Periodic Table from electronic configuration, building up by one electron at a time
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Avogadro Constant
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is approximately 6 x 1023 mol-1, the number of atoms per mole of 126C.
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bacteria (pl.) bacterium (sing)
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A simple microscopic microorganisms; there are few no organelles and only small loops of DNA called plasmids.
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binding site
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These are the reactive parts of large molecules; the site where molecules combine.
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blood transfusion
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An operation in which a patient's lost blood is replaced by blood from other people (donors). The bloods have to be from the same group.
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bond length
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the distance between a pair of atoms or ions in a compound
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bond polarity
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the ionic character of a bond resulting from the electronegativity difference between atoms
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bronchodilator
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A chemical which has the effect of opening up (dilating) the bronchii (airways) by causing the smooth muscle to relax.
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Br¯nsted-Lowry acid
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a proton donor in the presence of a solvent (Br¯nsted-Lowry base - proton acceptor)
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buffer solution
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a solution of a weak acid and the salt of a weak acid (or a weak base and the salt of a weak base) whose pH only changes slightly on the addition of acid or base or on dilution at a constant temperature
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catalyst
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A substance which when added to a reaction lowers the activation energy by providing an alternative reaction mechanism, and can be recovered unchanged in mass at the end of the reaction. The catalyst concentration does not appear in the equilibrium expression.
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cocaine
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local anaesthetic
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complex ion
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a metal cation surrounded by a number of ligands
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complex reaction
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One which proceeds by a number of elementary steps
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cracking
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the decomposition of a chemical substance by heating, sometimes involving a catalyst; this usually refers to a petroleum fraction being broken down into components of lower molar mass
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crystal-field theory
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A theory of the electronic structures of inorganic complexes, in which the complex is assumed to consist of a central metal atom or ion surrounded by ligands that are ions. E.g. [PtCl4]2- is throught of as a Pt2+ ion surrounded by four Cl- ions at the corners of a square. (abridged)
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dialysis
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A process for separating substances in solution through a selectively permeable membrane. This is used for people whose kidneys are not functioning properly, in order to filter waste urea from the blood and adjust salt balance.
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DNA
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This is the molecule which contains the genetic code within the nucleus. DNA is passed on from one generation to the next, which is the mechanism of inheritance.
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dynamic equilibrium
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a reversible reaction in which products are being converted into one another and vice-versa at a measurable rate
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electrocardiogram (ECG)
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A recording of the electrical activity of the heart on a moving strip of paper. This gives a picture of the heart action over a period of time.
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electron affinity
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The energy change for the process of bringing 1 mol of electrons from infinity to 1 mol of gaseous atoms for form 1 mol of gaseous uninegative ions at a stated temperarure and pressureX(g) + e- --> X-(g)
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electronegativity
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The power of an atom in a molecule or in a bond to attract electrons to itself
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electrophile
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molecule or ion which can form a new covalent bond using a pair of electrons provided by another molecule or ion; attracted to a negative centre
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elementary reaction
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One which proceeds by a single step, for which the order and molecularity must be identical. Elementary reactions are unlikely to be termolecular
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empirical formula
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The simplest whole number ratio of atoms in a compound
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Enthalpy Change of Atomisation
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The energy change at constant pressure for(i) an element, the formation of 1 mol of gaseous atoms;(ii) a compound, the formation of gaseous atoms from 1 mol of the compound;at a stated temperature
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enthalpy change of atomisation
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the energy change at constant pressure and a stated temperature for the process of separation a substance into its constituent atoms in the ground state in the gas phase. Usually fori) an element, the formation of 1 mol of gaseous atoms;ii) a compound, the formation of gaseous atoms from 1 mol of the compound
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Enthalpy Change of Combustion
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The energy change at constant pressure for the process of burning completely in oxygen (or sometimes fluorine) 1 mol of a substance at a stated temperature
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enthalpy change of hydration
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the energy change at constant pressure and a stated temperature for the process of bringing 1 mol of gaseous ions from infinity to form a solution in a specified volume of water containing 1 mol of hydrated ions.
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enthalpy change of neutralisation
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the energy change at constant pressure and a stated temperature for the process of reacting 1 mol of hydrated protons with an equivalent amount of base
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enthalpy change of reaction
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the energy change at constant pressure and a stated temperature for a process in which a specified amount of reactants is converted into products at a stated temperature and pressure
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enthalpy change of solution
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the energy change at constant pressure and a stated temperature for the process of dissolving 1 mol of a compound in a stated amount of water
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enzyme
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A protein which acts as a biological catalyst, speeding up the rate of chemical reactions within the body.
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equilibrium
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a reaction in whcih both reactants and products are present and are being dynamically converted into one another
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First Ionization Energy
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The energy change for the process of removing to infinity 1 mol of electrons from 1 mol of gaseous atoms to form 1 mol of gaseous unipositive ions at a stated temperature and pressureM(g) --> M+(g) + e-
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first ionization energy
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The energy change for the process of removing to infinity 1 mol of electrons from 1 mol of gaseous atoms to form 1 mol of gaseous unipositive ions at a stated temperature and pressure.M(g) --> M+(g) + e-
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First Law of Thermodynamics (a.k.a. Law of Conservation of Energy)
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There are several definitions possible of which one is: energy cannot be created nor destroyed, merely changed from one form to another
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fraction
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a mixture of similar chemical compuonds, the boiling points of which fall within a particular range and which are separated during fractional distillation
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fractional distillation
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the separation of a mixture of liquids into components by collecting distillates at different temperatures
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functional group
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an atom or a group of atoms attached to a hydrocarbon chain which has its own characteristic set of reactions
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fungi
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A group of micro-organisms including yeasts, moulds and mushrooms.
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gene
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A short piece of DNA which is responsible for the inheritance of a particular characteristic. It codes for the production of a specific protein.
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gene therapy
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A treatment of a disease caused by the absence or malfuntion of a gene. Gene therapy involves supplying the normal gene.
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genetically engineered virus
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A virus from which all harmful parts have been removed
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geometrical (cis-trans) isomers
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compounds with the same molecular formula but with different arrangements of the atoms in space due to non-rotation within the molecules
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H2 antagonist
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A class of anti-ulcer drugs which work through the inhibition of acid production by gastric glands, by inhibition of histamine H2 sites.
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Hallucinogens
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Hallucinogens are drugs that alter how people experience whatís going on around them. They may hear, see and think things which are not really happening. Peopleís experiences vary, just as dreams can be pleasant or nightmares. LSD is a hallucinogen.
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Hess' Law
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The enthalpy change accompanying a chemical change is independent of the route by which the chemical change takes place, all measurements being made at the same temperature and pressure
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heterolytic fission
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the breaking of a covalent bond in which the pair of electrons in the bond remains with one of the atoms involved
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homogeneous catalyst
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Is one in which it is in the same phase as the reactants: it is consumed by an early step, and regenerated in a later step of the complex mechanism; the concentration of the catalyst appears in the rate equation
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homologous series
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a family of organic compounds which has a general formula and a characteristic functional group; the members of the series have similar chemical properties and show a gradation of physical properties with increasing molar mass
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homolytic fission
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the breaking of a covalent bond in which each fragment retains one of the bonding pair of electrons
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hormone
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Special chemicals that are released by glands in the body. They carry messages to other parts of the body to control the body's activities, including growth, digestion and temperature control.
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Hund's rule of maximum multiplicity
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electrons occupy degenerate orbitals so as to give the maximum number of unpaired spins
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hydrogen bond
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a bond between hydrogen and an electronegative atom (especially O, N, and F) often weaker than a covant bond - typically in the order of 25% of the strength of a covalent bond.
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immune system
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The body system made up of cells and organs which defend against infection.
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Immunity
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The ability to resist or fight off a disease.
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immunity
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The ability to resist or fight off a disease.
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In vitro
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This term is given to processes that happen (within glass) in an artificial environment. In vitro fertilisation involves the fertilisation of eggs outside the body in artificial containers, and later implanting them in the body.
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in vitro
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This term is given to processes that happen (within glass) in an artificial environment. In vitro fertilisation involves the fertilisation of eggs outside the body in artificial containers, and later implanting them in the body.
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in vivo
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This term refers to a process happening within a living thing.
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infrared spectroscopy (IR spec.)
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A technique that measures the frequencies of infrared absorbed by a substance across the IR spectrum (approximately 3x1011 to 3x1014 Hz). The spectrum of IR absorptions can be used to assist the determination of molecular structure using the molecule's characteristic natural vibrational frequencies. The frequency is traditionally translated to the reciprocal of the wavelenth when expressed in cm. The resulting quantity known as the 'wavenumber' is measured in cm-1.
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insulin
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This is a hormone found in vertebrates and invertebrates. It is secreted by cells in response to high blood sugar levels, and causes the conversion of glucose to glycogen. Deficiency of insulin causes diabetes.
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isomers (general)
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compounds with the same molecular formula but with some different physical and sometimes some different chemical properties
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isotope
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one of two or more atoms or elements with the same proton number but different mass numbers: each isotope differs in the number of neutrons.
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lattice enthalpy
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the energy change at constant pressure and a stated temperature for the process of bringing 1 mol of gaseous component ions from infinity to their positions in the latticeExampleM+(g) + X-(g) ---> MX(s)
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Le Chatelier's Principle
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Any system in stable chemical equilibrium, when subjected to the influence of an external cause which tends to change either its temperature or condensation (pressure, concentration, number of molecules in unit volume), throughout or in only some of its parts, can undergo only such internal modificatins which, if they occurred on their own, would bring about a change of temperature or of condensation of a sign contrary to that resulting from the external cause.Translated from the French of Le Chatelier
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life expectancy
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The age to which someone might live. This varies between countries, socio-economic groups, and centuries.
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ligand
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a group, charged or uncharged, or an ion which bonds by a coordinate bond to a metal cation to form a complex ion: an electron-pair (Lewis base / nucleophile) which bonds by a coordinate bond to a metal cation to form a complex ion.
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liposome
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tiny artificial hollow sphere made from fatty compounds like cholesterol
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magnetic resonance imaging (MRI)
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A special technique used to image internal structures of the body, particularly soft tissues. Images are very clear and often more useful than X-rays.
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Markownikoff's Rule
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The negative part of the addendum adds to the less hydrogenated carbon atom.(Cave questions expecting stability of primary and secondary carbocations!)
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microbe
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A microscopic living thing such as bacteria, fungi and protoctista.
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mole
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The unit of amount of substance. One mole is that amount of substance which contains as many specified elementary particles are there are atoms in 0.012 Kg of the isotope 126C.
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molecular formula
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is a multiple of the empirical formula giving the number of atoms of each type in a molecule.
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Molecularity
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The number of particles participating in an elementary reaction
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neuro-transmitter
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A substance which acts as a messenger at synapses between neurones (the nerve cells which bring about actions/responses). Neurotransmitters are released at the ends of neurones, diffusing between adjacent cells.
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Neurotransmitter
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A chemical that conveys or inhibits nerve impulses between one nerve and another at a synapse in the brain. Illnesses such as depression or schizophrenia cause disturbance of the levels of these chemicals.
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normal flora
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The flora (or plant life) that grow quite normally and harmlessly on the body.
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nuclear magnetic resonance (NMR)
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A form of spectrometry using the precise absorption of electro magnetic radiation by a nucleus with nonzero magnetic moment in an external magnetic field. Such nuclei have 'spin' and consequently behave as small magnets. For hydrogen there are two possible quantum states 'spin up' and 'spin down', each with a slightly different energy. A transition of states from spin up to spin down results in a small change of energy state and the emission of a photon in the radio band of the e-m spectrum. This technique has been extended to the field of medicine where in magnetic resonance imaging (MRI) images of tissues are formed.
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nucleophile
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molecule or ion with an unbonded pair of electrons with which it can form a new covalent bond; attracted to a positive centre
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optical isomers
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compounds with the same molecular formula but with different arrangements of the atoms in space due to a chiral centre
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Order
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The power to which to the concentration of a species in the experimental rate equation is raised
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organ transplant
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An operation in which a person's damaged or diseased organ is replaced with a healthy organ from another person (donor). Kidneys, hearts, lungs and livers have all been successfully transplanted.
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Overall Order
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The sum of the power to which each concentration is raised in the experimental rate equation
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Oxidation states, rules for assigning
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1. Uncombined elements have an oxidation state of zeroIn compounds:-2. Fluorine has an oxidation state of -13. Oxygen has an oxidation state of -2 except in peroxides4. Hydrogen is +1 usually (but in ionic hydrides it is -1)5. The sum of the oxidation states in a compound is zero6. No oxidation state may be more than the group number.
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Painkillers
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Painkillers take away pain, as the name suggests. They stop people reacting to physical pain or emotional worries. Heroin is a painkiller.
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pathogen
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A disease producing organism.
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Pauli exclusion principle
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no two electrons may have the same set of four quantum numbersNo orbital can contain more than two electrons
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penicillin
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A well-known and commonly used antibiotic which has also been modified to produce other antibiotics. It is derived from the mould Penicillium notatum. It stops the growth of cell walls in bacteria, preventing the increase in population.
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Periodic Law
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The physical and chemical properties of the elements are in periodic dependence upon their atomic numbers.
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peristalsis
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The wave like movement caused by two sets of antagonistic muscles in tube like structures. In the gut, circular and longitudinal muscles bring about peristalsis by alternately contracting and relaxing in turn producing a wave action along the gut. This is similar to muscular action in animals such as Earthworms.
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pH
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(source: literally 'potential of Hydrogen')pH = - log10[H3O+]/moldm-3(you need to supply units, because you can only take a logarithm of a number)
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pi bond
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a molecular orbital consisting of regions of electron density above and below the line of centres between a pair of bonded atoms.
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proteins
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A family of long chain molecule based on carbon (and containing nitrogen and sulphur) that are part of all living things.
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proton
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A sub-atomic elementary particle, with unit positive charge and unit mass, expressed in relative atomic mass units (The actual mass is approximately 1.66 x 10-24 g).
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Protozoa
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A diverse group of single-celled microscopic living things. This group is now classed within the Protoctista.
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radical
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an excited atom or molecule with an unpaired electron
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radiotherapy
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The treatment of disease by ionising radiation, most commonly used in the treatment of cancer.
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rate constant
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The constant of proportionality in the experimental rate equation relating the rate to the concentration of the species raised to their appropriate orders
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reforming
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the rearrangement of the carbon chains of compounds, using elevated temperarures and pressures, and catalysts, to give molecules containing branches or rings
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relative atomic mass
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The ratio of the average mass per atom of an element relative to 1/12 the mass of an atom of 126C.
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relative molecular mass
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The sum of the relative atomic masses of the elements in a compound (or defined similarly to RAM: both are now obsolete).
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reversible reaction
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a reaction which can be made to proceed either forwards or backwards under suitable conditions; a reaction in which both products and reactants are present at equilibrium
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ribose nucleic acid (RNA)
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The chemical that translates the genetic code of DNA into proteins that make up the body.
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saturated hydrocarbon
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a hydrocarbon containing no carbon-carbon multiple bonds
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saturated solution
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a solution in which no more solute can dissolve without causing precipitation; a solution in whcih the ionic product equals the solubility product
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Sedatives
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Sedatives are drugs that slow down the nervous system. Alcohol is a sedative. Sedatives make people feel less anxious and more relaxed. But they also slow down physical reactions, and cause sleepiness or unconsciousness. A mixture of sedatives is dangerous because vital processes like the heartbeat get slower too. Sedatives may be addictive.
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sigma bond
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a molecular orbital of low energy whose region of electron density lies along the line of centres between a pair of bonded atoms
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spectrometry
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Techniques that measure the frequencies absorbed by a substance across a band of the e/m spectrum. A spectrum of absorptions can be used to assist the determination of molecular structure. Different techniques use different areas of the electromagnetic spectrum (e.g. visible, UV, IR). Also termed spectroscopy.
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spores
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Tiny reproductive cell produced by plants that don't have proper flowers or produce normal seeds.
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standard cell potential
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is the difference between the standard electrode potentials of the right-hand and left-hand electrodes in a specified cell at a stated temperature; = VR - VL
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Standard Conditions
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Standard pressure is 101325 Pa. There has been no internationally agreed standard of temperature, so this must always be stated. Commonly it is 273.15 K or 298 K. Definitions involving standard must include reference to the standard of pressure. Other enthalpy change definitions follow the pattern of the two above.
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standard electrode potential
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is the value of the standard emf of a cell in which molecular hydrogen is oxidised to solvated protons at the left hand electrode at a stated temperature [Note: standard conditions as above, with concentration of solvated protons being 1 moldm-3]
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Standard Enthalpy Change of Formation
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The energy change at constant pressure for the formation of 1 mol of a compound from its constituent elements in their standard states (stable forms at 101 325 Pa and a stated temperature)
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stereochemical formula
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shows the distribution in space of the atoms of a molecule
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stereoisomers
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compounds with the same structural formula but with a different arrangement of the atoms in space
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Stimulants
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Stimulants are drugs that speed up the bodyís reactions, making people feel more alert and less tired. Caffeine is a stimulant. But taken in high doses stimulants cause nervous anxiety and paranoia (being convinced the world is against you).
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structural formula
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shows the sequence in which the atoms in a molecule are linked; it may be written as a linear formula or as a displayed formula
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structural isomers
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compounds with the same molecular formula but with different structural formulae
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substitution
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a reaction in which one atom or group of atoms is exchanged for another
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substitution reaction
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a reaction in which one atom or group of atoms is exchanged for another atom or group of atoms
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surgery
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Any treatment that involves some sort of physical intervention - either rejoining broken bones or cutting out diseased tissue.
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synapse
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A connection between excitable cells such as nerve cells.
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transition element
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a d-block element forming one or more stable ions which have incompletely filled d-orbitals
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trepanning
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An ancient example of surgery where a hole was drilled into the skull, supposedly to let out evil spirits.
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ultrasound
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An imaging technique which uses high frequency sound waves. This is believed to be non-damaging and is used to view the developing fetus in the womb.
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ultraviolet-visible spectroscopy
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A technique that measures the frequencies of UV and visible light absorbed by a substance across the UV-vis spectrum (approximately 3x1014 to 3x1016 Hz). The spectrum of absorptions can be used to assist the determination of molecular structure using the molecule's characteristic natural vibrational frequencies.
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unsaturated hyrdocarbon
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a hydrocarbon containing one or more carbon-carbon multiple bonds
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vaccine
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A preparation of micro-organisms which are dead or made harmless, which is given to an animal to bring about the immune response and give protection from future infection
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virus
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A tiny microbe, measuring only 0.00002 to 0.00003 mm, that can cause infections, eg flu, warts, measles. A virus is not a complete cell but consists only of a protein coat surrounding genetic material. Viruses multiply inside other cells, usually killing them.
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X-ray
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X-rays are part of the electromagnetic spectrum with a much shorter wavelength than light. They travel through the body's tissues. However, they are absorbed differently by different tissues and bones. So they leave a shadow on photographic film that shows internal growths or broken bones.
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