Definitions Flashcards
boiling point
The temperature at which the pressure of the gas created above a liquid equals atmospheric pressure
condensation
the change of a gas into a liquid. this process is accompanied by the evolution of heat
diffusion
the process by which different substances mix as a result of the random motions of their particles
evaporation
a process occuring at the surface of a liquid involving the change of state of a liquid into a gas at a temperature below the boiling point. when a solution is heated, the solvent evaporates and leaves the solute behind.
freezing point
the temperature at which a substance freezes. this has the same value as the melting point
melting point
the temperature at which a solid begins to turn into a liquid. pure substances have a sharp melting point
anion
A negative ion. anions are attracted to the anode in electrolysis
atom
the smallest part of an element that can exist as a stable entity. it has a central nucleus containing neutrons and protons surrounded by electrons in shells. An atom contains equal numbers of protons and electrons
cation
a positive ion. cations are attracted to the cathode in electrolysis
chemical change
a permanent change in which a new substance is formed
compound
a substance formed by the chemical combination of two or more elements in fixed proportions.
diatomic molecule
a molecule containing two atoms
element
a substance that cannot be further divided into simpler substances by chemical methods.
ion
an atom or group of atoms that has either lost one or more electrons, making it positively charged or gained one or more electrons making it negatively charged.
isotopes
different atoms of the same element that have the same number or protons but different number of neutrons
Mass number (nucleon number)
the total number of protons and neutrons found in the nucleus of an atom, symbol A
mixture
two or more substances mixed together that can be separated by physical means
molecule
a group of atoms covalently bonded together
monatomic molecule
a molecule which exists of only one atom
oxidation
gain of oxygen or loss of electrons or increase in oxidation state
oxidising agent
a substance that oxidises another substance and is itself reduced
proton number ( atomic number)
the number of protons in the nucleus of an atom, symbol Z
redox reaction
a reaction which involves simultaneous oxidation and reduction.
reducing agent
a substance that reduces another substance and is itself oxidised.
reduction
loss of oxygen or gain or electrons or decrease in oxidation number
relative atomic mass (Ar)
the average mass of the isotopes of an element compared to 1/12 of the mass of an atom of 12C
Covalent bond
a chemical bond formed by the sharing of one or more pairs of electrons between two atoms
delocalised electrons
electrons that are spread out within a metal structure. the electrons are not attached to any one particular ion
giant ionic lattice
a regular arrangement of positive and negative ions held together by the electrostatic forces of attraction between ions
intermolecular force
a weak force of attraction between simple molecules
ionic bond
a strong electrostatic force of attraction between oppositely charged ions
lattice
a regular arrangement of atoms, molecules or ions in a solid
avogadro constant
6.02 x 10^23 the number of atoms, ions or molecules in one mole of a substance
empirical formula
a formula showing the simplest whole number ratio of atoms or ions present in a compound
molar mass
the mass of one mole of a compound. unit of g/mol
mole
the amount of substance which contains 6.02 x 10^23 atoms, ions or molecules
molecular formula
a formula showing the actual number and type of different atoms of each element present in one molecule of compound
relative formula mass Mr
the sum of the relative atomic masses of those elements shown in the formula of any substance
anode
the positive electrode. it is positively charged because electrons are drawn away from it
binary compound
a compound containing two elements chemically combined
cathode
the negative electrode. it is negatively charged because an excess of electrons move towards it
electrodes
the conducting rods by which electric current enters and leaves the electrolyte
electrolysis
the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current.
electrolyte
a liquid which will carry electric current and is chemically charged by it
inert electrode
an electrode that does not react with the electrolyte or the products of electrolysis. examples are carbon (graphite) and platinum
activation energy
Ea, is the minimum energy that colliding particles must have in order to react
bond energy
amount of energy required to break one mole of covalent bonds in gaseous molecules
endothermic reaction
absorbs thermal energy from the surroundings leading to a decrease in temperature of surroundings
enthalpy change
the transfer or thermal energy during a reaction is called the enthalpy change, delta H, for the reaction. is negative for exothermic reactions and positive for endothermic reactions
exothermic reaction
transfers thermal energy to the surroundings leading to an increase in temperature of the surroundings.
fossil fuels
fuels, such as coal, petroleum and natural gas, formed from the remains of plants and animals
fuel
a substance that can be conveniently used as a source of energy
oil refining
the process of converting petroleum into seperate fractions
catalyst
a substance which increases the rate of a chemical reaction and is chemically unchanged at the end of the reaction. a catalyst increases the rate of a chemical reaction by providing an alternative reaction path which has a lower activation energy
enzyme
enzymes are protein molecules which are biological catalysts
rate of reaction
a measure of the change which happens during a reaction in a single unit of time
reversible reaction
a chemical reaction that can go both forwards and backwards. once some of the products have been formed, they will undergo a chemical change once more to re-form the reactants
acid
a substance which dissolves in water, producing H+(aq) ions as the only positive ion. a proton donor.
alkali
a soluble base which produces OH- (aq) ions in water
anhydrous salt
a salt which has has its water of crystallisation removed
base
a substance which neutralises an acid, producing a salt and water as the only products. bases are oxides or hydroxides of metals. a proton acceptor
indicator
a substance that shows whether a substance is acidic or alkaline by changing colour
neutralisation
the process in which an acid reacts with a base to form water
pH scale
a scale running from 0 to 14 used express the acidity or alkalinity of a substance
saturated solution
a solution containing the maximum amount of dissolved solute in the solvent at a given temperature
water of crystallisation
water incorporated into the structure of a substance as it crystallises. e.g copper (II) sulfate pentahydrate
alkali metals
the six metallic elements in group 1 of the periodic table
electronic configuration
a shorthand method of describing the arrangement of electrons within each the electron shells of an atom
group (periodic table)
a vertical column of elements in the periodic table containing elements with the same number of electrons in their outer shell.
halogens
the elements found in group VII of the periodic table
noble gases
the elements in group VIII of the periodic table
periodic table
a table of elements arranged in order of increasing proton number
periods
the horizontal rows of elements in the periodic table . the atoms of elements in a period have the same number of occupied shells.
transition elements
the elements found in the centre of the periodic table between group II and III
alloy
a mixture of two or more metals or of a metal with a non metal
corrosion
the process that takes place when metals and alloys are chemically attacked by oxygen, water or any other substance found in their immediate environment
metals
a class of chemical elements which have a characteristic lustrous appearance and are good conductors of heat and electricity
rust
an orange-brown layer of hydrated iron (III) oxide found on the surface of iron and steel
sacrificial protection
a method of rust prevention in which a layer of more reactive metal is applied to the surface of iron or steel
catalytic converter
a device of converting pollutant exhaust gases from cars into less harmful emissions
fertiliser
a chemical substance added to soil to replace mineral salts to make plants grow more healthily
photosynthesis
the process by which green plants synthesise carbohydrates from carbon dioxide and water using light as the energy source and chlorophyll as the catalyst
pollution
the modification of the environment by human influence
addition reaction
a reaction in which an atom or group of atoms is added across a carbon-carbon double bond. in an addition reaction only one product is formed/
alkane
a saturated hydrocarbon that contains single bonds only
alkene
an unsaturated hydrocarbon in which there is at least one carbon-carbon double bond
displayed formula
a formula showing all the atoms and bonds in one molecule of a compound
functional group
the atom or group of atoms responsible for the characteristic reactions of a compound
homologous series
a family of similar compounds with similar chemical properties and the same functional group and general formula that display a trend in physical properties. Each member differs from the rest by a -CH2- unit
hydrocarbon
a compound made of molecules containing carbon atoms and hydrogen atoms only
monomer
a simple molecule that can be polymerised
polymer
a substance possessing very large molecules consisting of repeated units
saturated hydrocarbon
a formula showing how groups of atoms are arranged in a molecule
structural isomer
the existence of compounds with the same molecular formula but different structural formulae
substitution reaction
a reaction in which an atom or group of atoms is replaced by another atom or group of atoms
unsaturated hydrocarbon
a hydrocarbon in which there is at least one carbon-carbon double or triple bond
combustion
a chemical reaction in which a substance reacts rapidly with oxygen, producing heat and light
condensation polymer
a polymer formed by a condensation reaction ( a reaction in which a simple molecule, such as water, is produced during polymerisation).
fermentation
a series of biological reactions, catalysed by the enzymes in yeast.
functional group
an atom or group of atoms responsible for the characteristic chemical reactions of an organic compound
