The Chemistry Definitions Definiti ons List For O levels
Isotopes – Two or more atoms with the same number of protons but different number of neutrons. Ionic compounds – A giant lattice of positive and negative ions strongly held together by electrostatic forces of attraction. Covalent compounds – Small molecules loosely held together by weak intermolecular forces of attraction. Ionic Bonding – The transfer of electrons from a metallic atom to a non-metallic atom, in order to achieve noble gas configuration. Covalent Bonding – The sharing of electrons at the valence shell between two or more non-metallic atoms, in order to achieve noble gas configuration. Metallic Bonding – A lattice of positive (metallic) ions in the sea of delocalized electrons. Acids – Substances which dissociate to produce hydrogen ions when dissolved in water. Bases – Substances which accept hydrogen ions when reacting with an acid. Alkalis – Bases which are soluble in water. Concentration of an acid – The number of acid molecules dissolved per unit of water. Basicity of an acid – The number of H + ions that can be produced per molecule of acid dissolved. E.g. Monobasic acid – An acid which dissociates to produce one hydrogen ion per molecule of acid when dissolved in water. Strength of an acid – The percentage of acid molecules that will dissociate, to produce hydrogen ions, when dissolved in water E.g. Strong acid – An acid a cid which fully dissociates to produce hydrogen ions when dissolved in water. Acidic oxides – Non-metal oxides which react with bases to form salt and water. Basic oxides – Metal oxides which react with acids to form salt and water. Amphoteric oxides – Metal oxides which react with both bases and acids. Neutral oxides – Non-metal oxides which do not react with bases or acids. Salts – Neutral ionic compounds
Insoluble – Not able to be dissolved in a solvent. (Dependent on solvent) Precipitation – A method to prepare an insoluble salt by mixing 2 soluble salts together. Water of crystallization – Water molecules which have become part of a neutral compound to form a crystal. Thermal Decomposition – The breaking down of a compound through the action of heat. The kinetic particle theory – All matter is made up of discrete particles and that these particles are in constant random motion. Diffusion – The net movement of particles from a region of higher concentration to a region of lower concentration. Elements – Pure substances that cannot be split up into two or more simpler substances by chemical processes or by electricity. Compounds – Pure substances that contain two or more elements chemically combined. Mixtures – impure substances which contain two or more different type of substances which are not chemically combined together. (Physically combined together) Relative atomic mass – The average mass of one atom of a particular element as compared with 1/12 the mass of a carbon-12 isotope. In other words: Average mass of one atom of particular element 1/12 x mass of a carbon 12-isotope Relative molecular/formula mass – The average mass of one molecule of a particular substance as compared with 1/12 the mass of a carbon-12 isotope. Avogrado’s constant (L) – The value 6 x 10 23, which represents the number of particles in one mole of a substance Avogrado’s Law – One mole of any gas occupies a volume of 24 dm 3, under room conditions of 25°C and 1 atm. Periodic Table – A systematic method of classifying all elements, according to their proton numbers and electronic configuration. Periods – Horizontal rows in the periodic table which show elements with the same number of electron shells and hence, similar atomic radii.
Groups – Vertical columns in the periodic table which show elements that have the same number of valence electrons and hence, similar chemical properties. Metals – Atoms/elements which tend to give/lose electrons to form positive ions. Non-metals – atoms/elements which tend to take/accept electrons to form negative with the exception of noble gases. Metalliods – Elements which exhibit both metallic and non-metallic properties. (E.g. silicon and boron) Alkali metals – Group I elements which have one valence electron, and have a tendency to lose an electron to form ions with an ionic charge of 1+ charge. Halogens – Group VII elements which have seven valence electrons, and have a tendency to accept/take an electron to form ions with an ionic charge of 1- charge. Noble Gases – Group 0/VIII elements which have full valence shells, and hence are very unreactive. They do not form ionic or covalent bonds but exist naturally as monoatomic gases. Redox reaction – A reaction which involves reduction and oxidation of reactant particles to form its products. Reduction
- Loss of oxygen - Gain of hydrogen - Gain of electrons - Decrease in oxidation state
Oxidation
- Gain of oxygen - Loss of hydrogen - Loss of electrons - Increase in oxidation state
Oxidizing agents – A chemical/substance which causes other substances to be oxidized and in the process, itself gets reduced. Reducing agents – A chemical/substance which causes other substances to be reduced and in the process, itself gets oxidized. Alloys – Metals with other elements (metallic or non-metallic) mixed inside them. Ores – Impure samples of metal compounds which are minded for the purpose of extracting the metal. Rusting – The corrosion of iron. Iron is oxidized by water and oxygen to form hydrated iron (III) oxide. Protective layering – The coating of a physical barrier around an object (in this case, iron/steel), such that contact with oxygen and water is prevented.
Sacrificial Protection – The placing of a more reactive metal, e.g. Magnesium, in contact with the iron or steel object, such that the more reactive metal will give its electrons in place of the object, and hence corroding first before the object. Galvanizing – The iron or steel object is coated with a later of zinc. Flue gas Desulfurization – The process of removing sulfur dioxide from waste gases through the use of limestone. Electrolysis – The conduction of electricity by aqueous/molten neutral ionic compounds (electrolytes), leading to the decomposition of the ionic compounds (electrolytes). Electrolyte – The molten/aqueous ionic compounds which is decomposed through the process of electrolysis. Electrode – An electrical conductor which carries an electric current to the electrolyte. Electrolysis: Cathode – The electrode connected to the negative terminal of the electrical source that attracts positive cations. Electrolysis: Anode – The electrode connected to the positive terminal of the electrical source that attracts negative anions. Simple electric cell – the most basic component of a battery which coverts chemical energy into electricity. Simple Electric Cell: Cathode – The less reactive metal in a Simple Electric Cell which receives electrons from the more reactive metal. The electrons are passed on in to the electrolyte, attracting positive ions. Simple Electric Cell: Anode – The more reactive metal that ionizes to become positive ions by losing electrons which are then given to the cathode of the Simple Electric Cell. These positive ions attract negative ions in the solution. Salt Bridges – An inert electrolyte used in a Simple Electric Cell to complete the circuit. Endothermic reactions – Reactions in which the reactants take in energy from its surroundings in order to form its products and hence, chemical energy increases while heat energy decreases. Exothermic reactions – Reactions in which the reactants give out energy to its surroundings in order to form its products and hence, chemical energy decreases while heat energy increases. Enthalpy change (ΔH) – The measure of change in chemical energy in a reaction. Activation energy – The minimum amount of energy that chemical reactants must possess before a chemical reaction will take place.
Catalyst – Substances which increases the rate of a chemical reaction, but itself remaining chemically unchanged at the end of the reaction. Reversible reaction – A reaction in which the forward and backwards reactions occur simultaneously resulting in an equilibrium mixture of both products and reactants at the end of the reaction. Natural Gas – A mixture of gaseous fossil fuels, found in oil fields and natural gas fields, and mainly consists of methane. Petroleum – Commonly known as crude oil, it is a mixture of hydrocarbons which must be separated by fractional distillation for further use. Catalytic cracking – The process by which longer-chain hydrocarbons are converted into shorter-chain hydrocarbons and hydrogen, through the use of heat (450°C) and a catalyst (Al2O3 or SiO2). Hydrocarbon – A compound that is made up of only hydrogen and carbon atoms. a toms. Isomer – Two or more organic molecules which have the same molecular formula but different structural formula. Polyunsaturated – An organic molecule which contains more than one C=C bond. Substitution reaction – A chemical reaction in which a hydrogen atom on an alkane is replaced with another atom, such as chlorine. Addition reaction – A chemical reaction in which an unsaturated organic molecule combines with another substance or itself to form a single new molecule. Addition Polymerization – A chemical reaction in which many small unsaturated organic molecules combine to form a single macromolecule as the only product. Condensation – A chemical reaction in which two or more organic molecules combine to form a larger organic molecule, with the elimination of a small inorganic (such as water or hydrogen chloride) in the process. Condensation polymerization – A chemical reaction in which many small organic molecules combine to form a macromolecule, with the elimination of small inorganic molecules (such as water) in the process. Homologous series – A series of organic compounds that share a general formula, have similar chemical properties due to the presence of the same functional group, with each successive member increasing by CH 2 and showing a gradation in physical properties. Monomer – A small organic molecule which can join with many other small organic molecules to form a large macromolecule known as a polymer.
Polymer – A large molecule consisting or repeating structural units, formed by the reaction of many small organic molecules joining together. Polyester/Polyamide – A polymer with repeating ester/amide linkages in its structure. Hydrolysis – The breaking down of a compound through the action of water molecules. Functional Group – An atom or a group of atoms within the structure or an organic molecule which gives the molecule its characteristic properties. Biodegradable – A material that can be decomposed naturally by the action of bacteria.
