Ocr Chemistry A Level Key Definitions Module 1

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Isotopes

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Atoms of the same element with different numbers of neutrons

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Atomic (proton) number

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The number of protons in the nucleus of an atom

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MAss (nucleon) number

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The number of particles (protons and neutrons) in the nucleus

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Ion

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A positively/negatively charged atom or (covalently bonded) group of atoms (a molecular ion)

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Relative isotopic mass

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The mass of an atom of an isotope compared with one-twlfth of the mass of an atom of carbon-12

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Relative atomic mass

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(Ar) is the weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12

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Relative molecular mass

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(Mr) is the weighted mean mass of a molecule compared with one-twelfth of the mass of an atom of carbon-12

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Relative formula mass

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The weighted mean mass of a formula unit compared with one-twelfth of the mass of an atom of carbon-12

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Amount of substance

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The quantity whose unit is the mole. Chemists use 'amount of substance' as a means of counting atoms

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Avogadro constant

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(NA) the number of atoms per mole of the carbon-12 isotope (6.02 x 10^23 mol^-1)

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Mole

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The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope

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Molar mass (m)

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The mass per mole of a substance. The units of molar mass are g mol^-1

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Empirical formula

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The simplest whole-number ratio of atoms of each element present in a compound

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Molecule

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A small group of atoms held together by covalent bonds

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Molecular formula

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The actual number of atoms of each element in a molecule

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Molar volume

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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 dm^3 mol^-1

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Concentration

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The amount of solute, in mol, dissolved per 1 dm^3 of solution

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Standard solution

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A solution of known concentration. Standard solutions are normally used in titrations to determine unknown information about another substance

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Species

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Any type of particle that takes place in a chemical reaction

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Stoichiometry

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The molar relationship between the relative quantities of substances taking part in a reaction

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Acid

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A species that is a proton donor

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Base

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A species that is a proton acceptor

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Alkali

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A type of base that dissolved in water forming hydroxide ions (OH-)

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Salt

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Any chemical compound formed from an acid when a H+ ion from the acid has been replaced by a metal ion or anohther positive ion, such as the amonium ion, NH4+

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Cation

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A positively charged ion

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Anion

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A negatively charged ion

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Acid + Carbonate -->

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Salt + CO2 + H2O

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Acid + Base -->

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Salt + Water

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Acid + Alkali -->

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Salt + Water

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Hydrated

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Refers to a crystalline compound containing water molecules

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Anhydrous

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Refers to a substance that contains no water molecules

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Water of crystallisation

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Refers to water molecules that form an essential part of the crystalline structure of a compound

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Oxidation Number

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A measure of the number of electrons that an atom uses to bond with atoms of another element. Oxidation numbers are derived from a set of rules

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Oxidation

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The loss of electrons or an increase in oxidation number

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Reduction

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The gain of electrons or a decrease in the oxidation number

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Redox Reaction

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Is a reaction in which both reduction and oxidation take place

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Reducing agent

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A reagent that reduces (adds electron to) another species

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Oxidising agent

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A reagent that oxidises (takes electrons from) another species