Chemistry › Definitions › Group 2 and Group 7
Group 2 and Group 7 definitions
Every term the lessons in this unit define, lesson by lesson, worded as the lessons use them. Each lesson title links to its notes.
Group 2: trends down the group and reactions with water
- Oxidation
- The loss of electrons by a species, which raises its oxidation state.
- Reducing agent
- A species that donates electrons to another species, and is itself oxidised in doing so.
- First ionisation energy
- The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
- Second ionisation energy
- The energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.
- Shielding
- The repulsion of an outer electron by the electrons in inner shells, which reduces the attraction of the nucleus it feels.
- Atomic radius
- Half the distance between the nuclei of two bonded atoms of the same element.
- Metallic bonding
- The electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons.
- Basic oxide
- A metal oxide that reacts with an acid to form a salt and water.
- Batch process
- A process in which a fixed quantity of material is converted in one run, the reactor being emptied and refilled between runs.
- Redox reaction
- A reaction in which one species is oxidised and another is reduced, electrons being transferred from one to the other.
Group 2 compounds: solubility, uses and the sulfate test
- Sparingly soluble
- Dissolving only to a very small extent, so that most of the solid remains undissolved, as magnesium hydroxide does in water.
- Precipitate
- An insoluble solid formed when two solutions are mixed and ions in them combine.
- Flue-gas desulfurisation
- The removal of sulfur dioxide from the waste gases of a power station by reaction with a base such as calcium oxide or calcium carbonate.
- Neutralisation
- The reaction of an acid with a base, in which hydrogen ions react with hydroxide ions to form water.
- Spectator ion
- An ion present in the reaction mixture that is unchanged by the reaction and is left out of the ionic equation.
- Ionic equation
- An equation showing only the ions and other species that take part in a reaction, with spectator ions omitted.
- Flame test
- A test in which a compound is heated in a flame and the colour of the light emitted identifies the metal ion present.
- Thermal decomposition
- The breaking down of a compound into simpler substances by heating.
- Polarising power
- The ability of a cation to distort the electron cloud of a neighbouring anion; it increases with the charge of the cation and decreases with its size.
Group 7: trends down the group and displacement reactions
- Van der Waals forces
- Attractions between molecules caused by temporary dipoles inducing dipoles in neighbouring molecules; also called induced dipole–dipole forces.
- Electronegativity
- The power of an atom to attract the pair of electrons in a covalent bond.
- Oxidising agent
- A species that accepts electrons from another species, and is itself reduced in doing so.
- Reduction
- The gain of electrons by a species, which lowers its oxidation state.
- Displacement reaction
- A reaction in which a more reactive element takes the place of a less reactive one in a compound or in solution.
- Half-equation
- An equation for either the oxidation or the reduction part of a redox reaction, showing the electrons lost or gained.
- Bond enthalpy
- The enthalpy change when one mole of a given covalent bond is broken, with all species in the gaseous state.
- Thermal stability
- The resistance of a compound to decomposition when it is heated.
Halide ions, the silver nitrate test, concentrated sulfuric acid, and chlorine in water
- Reducing ability
- How readily a species donates electrons; for the halide ions it increases from F⁻ to I⁻.
- Gravimetric analysis
- Finding the amount of a substance by converting it into a precipitate of known formula, which is filtered, dried and weighed.
- Acidified silver nitrate
- Silver nitrate solution to which dilute nitric acid has been added, used to test for halide ions.
- Complex ion
- A central metal ion bonded to one or more ligands by coordinate bonds, as in [Ag(NH₃)₂]⁺.
- Disproportionation
- A reaction in which the same element is simultaneously oxidised and reduced.
- Sodium chlorate(I)
- NaClO, the bleaching and disinfecting compound formed when chlorine reacts with cold dilute sodium hydroxide.
- Hydrogen halide
- A compound of hydrogen and a halogen, HX, which forms misty white fumes in moist air.
- Strong acid
- An acid that is completely dissociated into ions in aqueous solution.
Also: Periodicity and Period 3 definitions · Transition metals definitions