Chemistry As Atoms And Reactions Definitions

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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 or 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-twelfth of the mass of an atom of carbon-12.

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Relative atomic mass

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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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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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The number of atoms per mole of the Carbon-12 isotope.

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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

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The mass per mole of a substance. The units of molar mass are g/mol

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Empirical formula

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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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Volume per mole of a gas. At room temperature and pressure the molar volume is about 24dm

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Concentration

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Amount of a solute in mol dissolved per dm of solution

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Standard solution

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Solution of known concentration. 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 part in a chemical reaction.

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Stoichiometry

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The molar relationship between the relative quantities of substances taking partin 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 dissolves in water forming Hydroxide ions.

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Salt

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Any chemical compound formed from an acid when a Hydrogen ion from the acid has been replaced by the metal ion or another positive ion.

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Cation

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Positively charged ion.

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Anion

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A negatively charged ion.

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Hydrated

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A crystalline compound containing water molecules.

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Anhydrous

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A substance that contains no water molecules.

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Water of crystallisation

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Water molecules that form an essential part of the crystalline structure of a compound.

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Oxidation number

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Measure of the number of electrons that an atom uses to bond with atoms of another element.

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Oxidation

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Loss of electrons or an increase in oxidation number.

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Reduction

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Gain of electrons or a decrease in oxidation number.

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Reducing agent

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A reagent that reduces (adds electrons to) another species.

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Oxidising agent

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A reagent that oxidises (takes electrons from) another species.