BSEH SS Chemistry key terms

The smallest repeating portion of a crystal lattice which, when repeated in three dimensions, generates the whole crystal; it is described by its edge lengths and the angles between them.

Solution properties that depend on the number of solute particles rather than on their identity: relative lowering of vapour pressure, elevation of boiling point, depression of freezing point and osmotic pressure.

For a solution of volatile liquids, the partial vapour pressure of each component equals its mole fraction in the liquid multiplied by the vapour pressure of the pure component at the same temperature.

The ratio of the observed colligative effect to the value expected for a non-dissociating solute; it equals the actual number of particles produced per formula unit in solution.

A liquid mixture that boils at a constant temperature and distils without any change in composition, because its vapour has the same composition as the boiling liquid.

An equation relating the potential of a cell or half-cell to its standard potential, the temperature and the reaction quotient of the species involved, usually written E = E° − (RT/nF) ln Q.

The potential of a half-cell measured at 298 K with every species at unit activity (1 M or 1 bar), referred to the standard hydrogen electrode, which is assigned a value of zero volts.

The conductance of a solution containing one mole of dissolved electrolyte, obtained by dividing conductivity by concentration; for weak electrolytes it rises on dilution as ionisation becomes more complete.

The mass liberated or deposited at an electrode is proportional to the charge passed, and for a fixed charge the masses of different substances are proportional to their equivalent masses.

The sum of the powers of the concentration terms in the experimentally determined rate law; it may be zero, fractional or negative and cannot be deduced from the balanced equation.

The number of reactant species that collide together in a single elementary step; it is a whole number, never more than three, and applies only to simple one-step reactions.

The minimum extra energy that colliding reactant molecules must possess if products are to form; it equals the threshold energy minus the average energy of the reactant molecules.

An expression showing how the rate constant changes with temperature, k = A e^(−Ea/RT), where A is the frequency factor and Ea the activation energy of the reaction.

The accumulation of gas or solute molecules on the surface of a solid or liquid rather than throughout its bulk, caused by unbalanced attractive forces at the surface.

The scattering of a beam of light by colloidal particles, which makes the path of the beam visible through the dispersion; it distinguishes a colloid from a true solution.

Heating an ore strongly in a limited supply of air to drive off water, carbon dioxide or other volatile impurities and to convert the ore into its oxide.

Heating a sulphide ore in a plentiful supply of air so that it is oxidised to the oxide with release of sulphur dioxide, often removing arsenic and antimony as volatile oxides.

A concentration method in which powdered ore is agitated with water, oil and a frothing agent, so that sulphide particles wetted by oil rise with the foam and are skimmed off.

The decreasing tendency of the outermost s-electrons to take part in bonding on descending a p-block group, which makes lower oxidation states increasingly stable for the heavier elements.

An ion or molecule that donates one or more lone pairs of electrons to the central metal atom or ion of a coordination entity, forming a coordinate (dative) bond.

The number of donor atoms directly bonded to the central metal ion in a complex; a single ligand may contribute more than one such bond if it is bidentate or polydentate.

The separation in energy of the d orbitals of a metal ion as ligands approach: in an octahedral field the t2g set lies below the eg set, the gap being called Δo.

The steady decrease in atomic and ionic radii across the lanthanoid series, because added electrons enter poorly shielding 4f orbitals while nuclear charge grows, making later lanthanoids chemically similar.

A nucleophilic substitution in which the leaving group departs first to give a carbocation, which the nucleophile then attacks; the rate depends only on the concentration of the substrate.

A one-step nucleophilic substitution in which the nucleophile attacks from the side opposite the leaving group, giving inversion of configuration; the rate depends on both substrate and nucleophile.

A test in which an alcohol is shaken with concentrated hydrochloric acid and anhydrous zinc chloride; tertiary alcohols turn cloudy at once, secondary on warming, primary hardly at all.

Preparation of an ether by treating a primary alkyl halide with a sodium alkoxide; the alkoxide attacks the halide in an SN2 step, so tertiary halides give mainly alkenes instead.

The formylation of phenol using chloroform and aqueous sodium hydroxide, which gives salicylaldehyde through a dichlorocarbene intermediate that attacks the aromatic ring.

A reaction in which an aldehyde or ketone having α-hydrogens forms a β-hydroxy carbonyl compound in dilute base; on heating this loses water to give an α,β-unsaturated carbonyl compound.

The disproportionation of an aldehyde that has no α-hydrogen, such as benzaldehyde, in strong alkali, giving equimolar amounts of the corresponding alcohol and carboxylate salt.

A test in which a compound containing the CH3CO– group, or ethanol, is warmed with iodine and sodium hydroxide to give a yellow precipitate of triiodomethane.

Conversion of a primary amide into a primary amine containing one carbon atom fewer, by heating the amide with bromine and aqueous or alcoholic potassium hydroxide.

A test for primary amines: warming the amine with chloroform and alcoholic potassium hydroxide produces an isocyanide, recognised by its very unpleasant smell.

The dipolar ion an amino acid forms in neutral solution, in which the carboxyl group has lost a proton and the amino group has gained one, so the molecule carries both charges.

The amide linkage –CO–NH– that joins two amino acids, formed with loss of water between the carboxyl group of one acid and the amino group of the next.

Loss of the native three-dimensional shape of a protein through heat, acid or other agents, which destroys its biological activity without breaking the peptide bonds in the chain.

The repeated joining of unsaturated monomer molecules such as ethene through their double bonds to build a long chain, with no small molecule lost during the process.

Heating natural rubber with sulphur or a sulphur compound to form cross-links between the polymer chains, making the rubber harder, stronger and less sensitive to temperature changes.

A chemical applied to living tissue such as skin or a wound to kill or inhibit micro-organisms and so prevent infection; it is generally milder than a disinfectant.

A medicine that relieves pain without causing loss of consciousness; aspirin acts partly by blocking prostaglandin synthesis, while paracetamol acts mainly on the central nervous system.