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AQA C2 Key Words
Key Words for AQA GCSE Chemistry Topic C2
| Term | Definition |
|---|---|
| Compound | A substance made when two or more elements are chemically bonded together. |
| Covalent Bond | The attraction between two atoms that share one, or more pairs of electrons. |
| Covalent Bonding | The attraction between two atoms that share one, or more pairs of electrons. |
| Delocalised Electron | bonding electron that is no longer associated with any one particular atom. |
| Dot and Cross Diagram | a drawing to show the arrangement of the outermost electrons only of the atoms or ions in substance. |
| Double Bond | a covalent bond formed by the sharing of two pairs of electrons. |
| Giant Covalent Structure | a huge 3D network of covalently bonded atoms. (e.g. the giant lattice of carbon atoms in diamond or graphite. |
| Giant Lattice | a huge 3D network of atoms or ions (e.g. the giant ionic lattice in sodium chloride). |
| Ion | a charged particle produced by the loss or gain of electrons. |
| Ionic Bond | the electrostatic force of attraction between positively and negatively charged ions. |
| Ionic Bonding | the electrostatic force of attraction between positively and negatively charged ions. |
| Mixture | when some elements or compounds are mixed together and intermingle but do not react together ( i.e. no new substances are made). A mixture is NOT a pure substance. |
| Macromolecule | A Giant covalent structure. e.g. diamond- the diamond in a ring is one massive moleucule |
| Monomers | Small reactive molecules that react together in repeating sequences to form a very large molecule (a polymer). |
| Nanoscience | The study of very tiny particles or structures between 1 and 100 nanometres in size- where 1 nanometre = 1x10-9metres |
| Polymer | A substance made from very large molecules made of many repeating units e.g. poly(ethene). |
| Polymerisation | The reaction of monomers to make a polymer. |
| Atomic Number | The number of protons (which equals the number of electrons) in an atom. It is sometimes called the proton number. |
| Empirical Formula | The simplest ratio of elements in a compound. |
| Isotope | Atom that has the same number of protons but a different number of neutrons. i.e. the same atomic number but a different mass number. |
| Mass Number | The number of protons plus the number of neutrons in the nucleus of an atom. |
| Mole | The amount of substance in the relative atomic or formula mass of a substance in grams. |
| Molecular Formula | The chemical formula that shows the actual numbers of atoms in a particular molecule (e.g. C2H4). |
| Percentage Yield | The actual mass of product collected in a reaction divided by the maximum mass that could have been formed in theory, multiplied by 100. (i.e. (actual yield/theoretical yield) x 100) |
| Relative Atomic Mass,Ar | The average mass of the atoms of an element compared to carbon-12 (which is given the mass of exactly 12). The average mass must take into account the proportions of the naturally occurring isotopes of the element. |
| Relative Formula Mass, Mr | The total of the relative atomic masses, added up in the ratio shown in the chemical formula, of a substance. |
| Reversible Reaction | A reaction in which the products can re-form the reactants. |
| Symbol Equation | A balanced chemical equation showing the formula for each reactant and product in the reaction e.g. H2 + Cl2 = 2HCl |
| Word Equation | A way of describing what happened in a chemical reaction by showing the names of all the reactants and products they form. |
| Chromatography | The process by which small amounts of dissolved substances are separated by running a solvent along a material such as absorbent paper. |
| Gas Chromatography | The process of separating the components in a mixture by passing the vapours through a column and detecting them as they leave the column at different times. |
| Equilibrium | The point in a reversible reaction in which the forward and backward rates of reaction are the same. Therefore, the amount of substances present in the reacting mixture remain constant. |
| Mass Spectrometer | A machine that can be used to analyse small amounts of a substance to identify it and to find its relative molecular mass. |
| Molecular Ion Peak | The peak on the mass spectrum of a substance which tells us the relative molecular mass of the substance. The peak is produced by the heaviest positive ion shown on the mass spectrum. |
| Catalyst | A substance that speeds up a chemical reaction but remains chemically unchanged itself at the end of the reaction. |
| Collision Theory | An explanation of chemical reactions in terms of reacting particles colliding with sufficient energy for a reaction to take place. |
| Endothermic | A reaction that takes in energy from the surroundings. |
| Exothermic | A reaction that gives out energy to the surroundings. |
| Activation Energy | The minimum energy needed to start off a reaction. |
| Acid | A sour substance which can attack metal, clothing or skin. The chemical opposite of an alkali. When dissolved in water, its solution has a pH number of less than 7. Acids are proton (H+ ion) donors. |
| Alkali | Its solution has a pH of more than 7. |
| Aluminium | A low density, corrosion resistant, metal used in many alloys including those used in the aircraft industry. |
| Aqueous Solution | The mixture made by adding a soluble substance to water. |
| Base | The oxide, hydroxide or carbonate of a metal that will react with an acid, forming a salt as one of the products. (If the base dissolves in water it is called and alkali). Bases are proton (H+ ion) acceptors. |
| Brine | A solution of sodium chloride in water. |
| Electrolysis | The breakdown of a substance containing ions by electricity. |
| Electrolyte | A liquid, containing free-moving ions, that is broken down by electricity in the process of electrolysis. |
| Half Equation | An equation that describes reduction (gain of electrons) or oxidation (loss of electrons), such as the reactions that take place at the electrodes during electrolysis. |
| Neutral | A solution with a pH value of 7 which is neither acidic nor alkaline. Alternatively, something that carries no overall electronic charge- neither positively or negatively charged. |
| Neutralisation | The chemical reaction of an acid with a base in which they cancel each other out, forming a salt and water. If the base is a carbonate or hydrogencarbonate, carbon dioxide is also produced in the reaction. |
| Oxidation | The reaction when oxygen is added to a substance (or when electrons are lost). |
| Oxidised | A reaction when oxygen is added to a substance (or when electrons are lost). |
| pH Scale | A number which shows how strongly acidic or alkaline a solution is. Acids have a pH value of less than 7 (pH 1 is strongly acidic). Alkalis have a pH value above 7 (pH 14 is strongly alkaline). A neutral liquid has a pH value of 7. |
| Reduction | A reaction in which oxygen is removed (or electrons are gained). |
| Salt | A compound formed when some or all of the hydrogen in an acid is replaced by a metal ( or by an ammonium ion). For example, potassium nitrate KNO3 (from nitric acid) |
| Universal Indicator | A mixture of indicators which can change through a range of colours depending on the pH of the solution. Its colour is matched to a pH number using a pH scale. It shows how strongly acidic or alkaline liquids and solutions are. |
Created by:
willocka
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