The Chemistry Definitions
Definiti ons List For O levels
Isotopes – Two or more atoms with the same number of protons but different number
of neutrons.
Ionic compounds – A giant lattice of positive and negative ions strongly held together
by electrostatic forces of attraction.
Covalent compounds – Small molecules loosely held together by weak intermolecular
forces of attraction.
Ionic Bonding – The transfer of electrons from a metallic atom to a non-metallic
atom, in order to achieve noble gas configuration.
Covalent Bonding – The sharing of electrons at the valence shell between two or more
non-metallic atoms, in order to achieve noble gas configuration.
Metallic Bonding – A lattice of positive (metallic) ions in the sea of delocalized
electrons.
Acids – Substances which dissociate to produce hydrogen ions when dissolved in
water.
Bases – Substances which accept hydrogen ions when reacting with an acid.
Alkalis – Bases which are soluble in water.
Concentration of an acid – The number of acid molecules dissolved per unit of water.
Basicity of an acid – The number of H + ions that can be produced per molecule of acid
dissolved.
E.g. Monobasic acid – An acid which dissociates to produce one hydrogen ion per
molecule of acid when dissolved in water.
Strength of an acid – The percentage of acid molecules that will dissociate, to produce
hydrogen ions, when dissolved in water
E.g. Strong acid – An acid
a cid which fully dissociates to produce hydrogen ions when
dissolved in water.
Acidic oxides – Non-metal oxides which react with bases to form salt and water.
Basic oxides – Metal oxides which react with acids to form salt and water.
Amphoteric oxides – Metal oxides which react with both bases and acids.
Neutral oxides – Non-metal oxides which do not react with bases or acids.
Salts – Neutral ionic compounds
Insoluble – Not able to be dissolved in a solvent. (Dependent on solvent)
Precipitation – A method to prepare an insoluble salt by mixing 2 soluble salts
together.
Water of crystallization – Water molecules which have become part of a neutral
compound to form a crystal.
Thermal Decomposition – The breaking down of a compound through the action of
heat.
The kinetic particle theory – All matter is made up of discrete particles and that these
particles are in constant random motion.
Diffusion – The net movement of particles from a region of higher concentration to a
region of lower concentration.
Elements – Pure substances that cannot be split up into two or more simpler
substances by chemical processes or by electricity.
Compounds – Pure substances that contain two or more elements chemically
combined.
Mixtures – impure substances which contain two or more different type of substances
which are not chemically combined together. (Physically combined together)
Relative atomic mass – The average mass of one atom of a particular element as
compared with 1/12 the mass of a carbon-12 isotope.
In other words:
Average mass of one atom of particular element
1/12 x mass of a carbon 12-isotope
Relative molecular/formula mass – The average mass of one molecule of a particular
substance as compared with 1/12 the mass of a carbon-12 isotope.
Avogrado’s constant (L) – The value 6 x 1023, which represents the number of
particles in one mole of a substance
Avogrado’s Law – One mole of any gas occupies a volume of 24 dm3, under room
conditions of 25°C and 1 atm.
Periodic Table – A systematic method of classifying all elements, according to their
proton numbers and electronic configuration.
Periods
rowsand
in the
periodic
table
which
show elements with the same
number –ofHorizontal
electron shells
hence,
similar
atomic
radii.
Groups – Vertical columns in the periodic table which show elements that have the
same number of valence electrons and hence, similar chemical properties.
Metals – Atoms/elements which tend to give/lose electrons to form positive ions.
Non-metals – atoms/elements which tend to take/accept electrons to form negative
with the exception of noble gases.
Metalliods – Elements which exhibit both metallic and non-metallic properties. (E.g.
silicon and boron)
Alkali metals – Group I elements which have one valence electron, and have a
tendency to lose an electron to form ions with an ionic charge of 1+ charge.
Halogens – Group VII elements which have seven valence electrons, and have a
tendency to accept/take an electron to form ions with an ionic charge of 1- charge.
Noble Gases – Group 0/VIII elements which have full valence shells, and hence are
very unreactive. They do not form ionic or covalent bonds but exist naturally as
monoatomic gases.
Redox reaction – A reaction which involves reduction and oxidation of reactant
particles to form its products.
Reduction
- Loss of oxygen
- Gain of hydrogen
- Gain of electrons
- Decrease in oxidation state
Oxidation
- Gain of oxygen
- Loss of hydrogen
- Loss of electrons
- Increase in oxidation state
Oxidizing agents – A chemical/substance which causes other substances to be
oxidized and in the process, itself gets reduced.
Reducing agents – A chemical/substance which causes other substances to be reduced
and in the process, itself gets oxidized.
Alloys – Metals with other elements (metallic or non-metallic) mixed inside them.
Ores – Impure samples of metal compounds which are minded for the purpose of
extracting the metal.
Rusting – The corrosion of iron. Iron is oxidized by water and oxygen to form
hydrated iron (III) oxide.
Protective
The coating
of a physical
barrier
an object (in this case,
iron/steel),layering
such that– contact
with oxygen
and water
is around
prevented.
Sacrificial Protection – The placing of a more reactive metal, e.g. Magnesium, in
contact with the iron or steel object, such that the more reactive metal will give its
electrons in place of the object, and hence corroding first before the object.
Galvanizing – The iron or steel object is coated with a later of zinc.
Flue gas Desulfurization – The process of removing sulfur dioxide from waste gases
through the use of limestone.
Electrolysis – The conduction of electricity by aqueous/molten neutral ionic
compounds (electrolytes), leading to the decomposition of the ionic compounds
(electrolytes).
Electrolyte – The molten/aqueous ionic compounds which is decomposed through the
process of electrolysis.
Electrode – An electrical conductor which carries an electric current to the electrolyte.
Electrolysis: Cathode – The electrode connected to the negative terminal of the
electrical source that attracts positive cations.
Electrolysis: Anode – The electrode connected to the positive terminal of the
electrical source that attracts negative anions.
Simple electric cell – the most basic component of a battery which coverts chemical
energy into electricity.
Simple Electric Cell: Cathode – The less reactive metal in a Simple Electric Cell
which receives electrons from the more reactive metal. The electrons are passed on in
to the electrolyte, attracting positive ions.
Simple Electric Cell: Anode – The more reactive metal that ionizes to become
positive ions by losing electrons which are then given to the cathode of the Simple
Electric Cell. These positive ions attract negative ions in the solution.
Salt Bridges – An inert electrolyte used in a Simple Electric Cell to complete the
circuit.
Endothermic reactions – Reactions in which the reactants take in energy from its
surroundings in order to form its products and hence, chemical energy increases while
heat energy decreases.
Exothermic reactions – Reactions in which the reactants give out energy to its
surroundings in order to form its products and hence, chemical energy decreases
while heat energy increases.
Enthalpy change (ΔH) – The measure of change in chemical energy in a reaction.
Activation
energy
– The minimum
amount
energy that chemical reactants must
possess
before
a chemical
reaction will
takeofplace.
Catalyst – Substances which increases the rate of a chemical reaction, but itself
remaining chemically unchanged at the end of the reaction.
Reversible reaction – A reaction in which the forward and backwards reactions occur
simultaneously resulting in an equilibrium mixture of both products and reactants at
the end of the reaction.
Natural Gas – A mixture of gaseous fossil fuels, found in oil fields and natural gas
fields, and mainly consists of methane.
Petroleum – Commonly known as crude oil, it is a mixture of hydrocarbons which
must be separated by fractional distillation for further use.
Catalytic cracking – The process by which longer-chain hydrocarbons are converted
into shorter-chain hydrocarbons and hydrogen, through the use of heat (450°C) and a
catalyst (Al2O3 or SiO2).
Hydrocarbon – A compound that is made up of only hydrogen and carbon aatoms.
toms.
Isomer – Two or more organic molecules which have the same molecular formula but
different structural formula.
Polyunsaturated – An organic molecule which contains more than one C=C bond.
Substitution reaction – A chemical reaction in which a hydrogen atom on an alkane is
replaced with another atom, such as chlorine.
Addition reaction – A chemical reaction in which an unsaturated organic molecule
combines with another substance or itself to form a single new molecule.
Addition Polymerization – A chemical reaction in which many small unsaturated
organic molecules combine to form a single macromolecule as the only product.
Condensation – A chemical reaction in which two or more organic molecules
combine to form a larger organic molecule, with the elimination of a small inorganic
(such as water or hydrogen chloride) in the process.
Condensation polymerization – A chemical reaction in which many small organic
molecules combine to form a macromolecule, with the elimination of small inorganic
molecules (such as water) in the process.
Homologous series – A series of organic compounds that share a general formula,
have similar chemical properties due to the presence of the same functional group,
with each successive member increasing by CH2 and showing a gradation in physical
properties.
Monomer – A small organic molecule which can join with many other small organic
molecules to form a large macromolecule known as a polymer.
Polymer – A large molecule consisting or repeating structural units, formed by the
reaction of many small organic molecules joining together.
Polyester/Polyamide – A polymer with repeating ester/amide linkages in its structure.
Hydrolysis – The breaking down of a compound through the action of water
molecules.
Functional Group – An atom or a group of atoms within the structure or an organic
molecule which gives the molecule its characteristic properties.
Biodegradable – A material that can be decomposed naturally by the action of
bacteria.