Glossary Part 3

Finally, P - T of the glossary. All the terms come from the glossary of this book. Remember, you can download the entire glossary from here.

P

Periodicity -
The regular recurrence of the properties of elements when they are arranged in atomic number order as in the Periodic Table.

Period -
A horizontal row of elements in the Periodic Table. There are trends in the properties of the elements as we cross a period.

Propagation -
One of the steps of a chain reaction in which a free radical converts reactant into product and another free radical is formed which can take part in another propagation step.

Proton -
A positively charged sub-atomic particle found in the nuclei of atoms.

R

Redox -
Short for reduction-oxidation, it describes reactions in which electrons are transferred from one species to another.

Reducing Agent -
A reagent that reduces (adds electron to) another species.

Reduction -
A reaction in which an atom or group of atoms gains electrons.

S

Shielded Nuclear Charge -
(also called effective nuclear charge). The positive charge from the nucleus that is felt by the outer electrons of an atom - it is the total number of positive charges on the nucleus of an atom minus the total number of inner electrons.

Specific Heat Capacity, c -
The amount of heat needed to raise the temperature of 1g of substance by 1K.

Spectator Ions -
Ions that are unchanged during a chemical reaction i.e. they take no part in the reaction.

Standard Molar Enthalpy Change of Combustion -
The amount of heat energy given out when 1 mole of a substance is completely burned in oxygen at standard conditions (298K and 100kPa).

Standard Molar Enthalpy Change of Formation -
The heat change when 1 mole of substance is formed from its elements at standard conditions (298K and 100kPa).

Stoichiometric -
Describes the simple whole number ratios in which chemical species react.

Strong Nuclear Force -
The force that holds protons and neutrons together whithin the nucleus of an atom.

T

Termination -
The stage of a chain reaction in which two free radicals combine together to give a species that is not a free radical.

Thermal Decomposition -
The breakdown of a compound by heat.

Thermochemical Cycle -
A sequence of chemical reactions (with their enthalpy changes) that convert a reactant into a product. The total enthalpy change of the sequence of reactions will be the same as that for the conversion of the reactant to the prduct directly (or by any other route).