Definitions Flashcards
Element
A substance that cannot be broken down into simpler substances by chemical means or produced by combining simpler substances.
Metal
Any element that loses electrons to form a positive ion (cation).
Atomic number
The number of protons present in the nucleus of an atom.
Mass number
The mass number is the number of protons plus neutrons present in the nucleus of an atom.
Isotopes
Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.
Relative atomic mass number
The average mass of an atom of an element compared to 1/12 the mass of the carbon-12 isotope, taking relative abundances of the naturally occurring isotopes into account.
Relative molecular mass number
The average mass of a molecule of a compound compared to 1/12 the mass of the carbon-12 isotope, taking relative abundances of the naturally occurring isotopes into account.
Compound
A compound is a substance that is made up of two or more elements combined together chemically.
The octet rule
This rule states that when atoms bond, most atoms tend to want an electron arrangement of eight electrons in their outermost shell (energy level).
Valency
The valency of an atom tells us the number of chemical bonds an atom can form.
Radioactivity
Is the spontaneous disintegration of the nucleus with the emission of α, β or y radiation.
Nuclear reaction
A nuclear reaction involves a change in the nucleus of an atom and a new element is usually formed as a result.
Chemical reaction
A chemical reaction involves electrons being shared or transferred from one atom to another - the nucleus of the atom remains the same.
Half-life
This is the time taken for half the nucLEI in a given sample size to decay.
The principle of the mass spectrometer
The principle involved is that different ions are separated according to their masses when moving in a magnetic field.
Absorption spectrum
An absorption spectrum is a series of dark lines against a coloured background.
Emission spectrum
An emission spectrum is a series of coloured lines against a dark background.
Heisenberg’s uncertainty principle
This states that it is impossible to know both the position and the speed of an electron at the same time as electrons move in a wave motion.
Atomic orbital
An atomic orbital is a region in space around the nucleus of an atom in which there is a high probability of finding an electron.
Energy level
Is the discrete amount of energy an electron has when it is in an atom.
Energy sublevel
A group of atomic orbitals within an atom, all of which have the same energy.
Aufbau principle
Electrons occupy the lowest available energy level.
Hunds rule of maximum multiplicity
When two or more orbitals of equal energy are available (i.e 2px 2py 2pz), electron fill them singly before filling them in pairs.
Pauli exclusion principle
No more than two electrons can occupy an orbital and this they can only do if they have opposite spin.
A mole
A mole of a substance is that amount of it which contains the Avogadro’s constant number of particles.
Avogadro’s constant
Is the number of carbon atoms in exactly 12 grams of the C-12 isotope. This equals 6 x 10(23) particles.
Avogadro’s law
Equal volumes of all gases measured at the same temperature and pressure contain equal numbers of molecules.
Molar mass
The mass of one mole of a substance is its relative atomic mass (Ar) expressed in grams.
Molar volume
At s.t.p the volume of 1 mole of any gas is 22.4 litres (22,400 cm3).
Atomic radius (covalent radius)
The atomic radius is obtained by getting half the distance between the centers of singly bonded atoms of the same element.
Alkali
An alkali is a base that is soluble in water.
Energy sublevel
A group of atomic orbitals within an atom, all of which have the same energy.
Transition element
An element that forms at least one ion with a partially filled d-sublevel.
D-block element
An element whose highest energy electron enters a d-orbital.
Acids - Arhenius’ theory
An acid produces H⁺ ions in water.
Monobasic acid
A monobasic acid produces one H⁺ ion in solution eg. HCl
Dibasic acid
A dibasic acid produces two H⁺ ions in solution e.g H₂SO₄.
Tribasic acid
A tribasic acid produces three H⁺ ions in solution e.g H₃PO₄.
Bases - Arrhenius’ theory
A base produces OH- ions in water.
Acid - Bronsted-Lowry theory
An acid is a proton (H⁺) donor.
Base - Bronsted-Lowry theory
A base is a proton (H⁺) acceptor.
Amphoteric
A substance that can act as both an acid and a base.
Conjugate pairs
Two substances that differ by one proton.
Salts
A salt is formed when the H⁺ of the acid is replaced by a metal or NH₄⁺.
Strong acid
A strong acid is an acid that fully dissociates in solution and is a good proton donor.
Weak acid
A weak acid is a poor proton donor and only slightly dissociates in solution.
Conjugate acid
A base plus a H⁺ ion.
Conjugate base
An acid minus a H⁺ ion.
Ionic bond
An ionic bond is formed due to the electrostatic attraction between oppositely charged ions caused by the complete transfer of electrons from one atom to another.
Electronegativity
The relative power of attraction of an atom of an element for the shared pair of electrons in a covalent bond.
Oxidation
Oxidation of an element occurs when the element loses electrons.
Reduction
Reduction of an element occurs when the element gains electrons.
Oxidation number
The oxidation number of an element is the charge an element has or appears to have when it is in compound when certain rules are applied.
Oxidation in terms of oxidation numbers.
Oxidation is an increase in oxidation number.
Reduction in terms of oxidation numbers.
Reduction is a decrease in oxidation number.
Boyles law
When a fixed mass of gas is kept at constant temperature, its volume multiplied by its pressure is constant.
Charles law
This states that the volume of a fixed mass of gas, kept at constant pressure, is directly proportional to the absolute temperature (kelvin).
Gay-Lussac’s Law of combining volumes
This states that gases always react with each other in simple whole number ratios when the volumes are measured at the same temperature and pressure.
Avogadro’s Law
This states that equal volumes of gases measured under the same conditions of temperature and pressure contain equal numbers of molecules.
An ideal gas
An ideal gas is defined as a gas that obeys all gas laws at all temperatures and pressures.
First ionisation energy
The minimum amount of energy required to remove the first most loosely bound electron from a mole of isolated atoms of an element in its neutral gaseous ground state
Limiting reactant
the reactant that is fully consumed when a reaction goes to completion
theoretical yield
the quantity of product that should form when all of the limiting reactant reacts (from the molar ratio of the equation)
compound
a substance that is made up of 2 or more elements combined together chemically
sigma bonding
when orbitals overlap ‘head on’. can occur between 2 s orbitals, and s and a p or 2 p orbitals
pi bonding
when orbitals overlap side ways. can happen between 2 p orbitals only
pure covalent bond
occurs when electrons are shared equally
polar covalent bond
occurs when electrons are shared unequally
dative covalent bond
only one atom supplies the electrons need to make the covalent bond, one atom supplies both of the electrons
polar molecule
the slight positive and slight negative poles of a molecule are separated by a distance, they do not coincide
hydrogen bonding
an intermolecular force of attraction that occurs when hydrogen is bonded to a small more electronegative element such as N,O or F
standard solution
a solution of known concentration
primary standard
a substance that is available in 100% purity, is stable in air, has a high molecular mass for accuracy and dissolves readily in water, can be made up to a standard solition directly
secondary standard
is a substance that is not available in 100% purity, is not stable in air, has a low molecular mass and does not dissolve readily in water, can not be made up to a standard solution directly
standardise
to find out the concentration of a solution by titration or colorimetry
Valence shell electron repulsion theory
pairs of electrons in the outer shell of an atom arrange themselves to be as far away from each other as possible to minimise the repulsions between them
lone pairs of electrons
pairs of electrons in the outer shell of the atom that do not take part in bonding
bonding pairs of electrons
pairs of electrons in the outer shell that are shared between atoms
heat of reaction
the heat change that occurs when a reaction takes place according to the balanced chemical equation
exothermic reaction
a reaction where heat is lost from the reaction to the surroundings
endothermic reaction
a reaction where heat is taken in by the reaction from the surroundings
heat of combustion
the heat change that occurs when 1 mole of a substance is burned in an excess of oxygen
heat of formation
the heat change that occurs when 1 mole of a substance is formed from its elements in their standard states
kilogram calorific value
the heat that is produced when 1 kilogram of a fuel is burned in an excess of oxygen
Hess’ law
when a reaction takes place in stages the sum of the heat changes of the individual stages equals the heat change that would occur if the reaction were to take place in one stage
hydrocarbon
a compound that only consists of the elements hydrogen and carbon
saturated
single bonds around the carbon atoms
unsaturated
a multiple bon present between two carbon atoms
aromatic
contains a benzene ring in the structure
aliphatic
straight or branched chained molecule
ionic addition reaction
2 reactants to form one main product
free radical substitution reaction
an atom or group of atoms in replaced by an atom or group of atoms to form 2 main products
condensation reaction
2 different molecules combine to form a more complex molecule with the production of a smaller molecule such as water
esterification reaction
an alcohol and a carboxylic acid react reversibly to form an ester and water (an example of a condensation reaction)
elimination reaction
a smaller molecule is removed from a larger molecule. a double bond is formed in one of the product molecules
dehydration reaction
removal of water from a molecule (an elimination reaction)
hydrogenation reaction
addition of hydrogen to an alkene molecule involving a nickel catalyst and 200ºC
heterolytic fission
a molecule splits up to form 2 different ions
homolytic fission
a molecule splits to form 2 identical atoms using u.v light
polymerisation reaction
a reaction where many small molecules called monomers combine together to form a very large molecule called a polymer
principle of the mass spectrometer
separation of ions based on them having different masses when moving in an magnetic field
principle of fractional distillation
separation of components of crude oil based on them having different boiling points
principle of steam distillation
two immiscible liquids together have a lower boiling point than either of the liquids of their own
principle of chromatography
a mobile phase carries a mixture through a stationary phase, separation happens because of some of the components of a mixture are attracted to significantly different extents to the mobile or stationary phase
principle of recrystallisation
more solute is soluble in hot solvent than in a cold one
principle of colorimetry
concentration of solute is proportional to colour intensity of solution
chemical equilibrium
a system is said to have reached a state of equilibrium when the rate of the forward reaction equals the rate of the reverse reaction
dynamic equilibrium
the forward and reverse reactions occur at the same time
Le Chatelier’s principle
when a system at equilibrium is subjected to a stress such as change in temperature, pressure or concentration thy system will alter to oppose the effect of the stress
reversible reaction
both forward and reverse reactions happen
electrolyte
a substance that in the molten or dissolved state can conduct electricity
electrochemical series
a list of elements arranged in order of their tendency to lose electrons
displacement reaction
a reaction where a metal will take the place of a less reactive metal from a solution of its salts
electrolysis
a process that uses electricity to bring about a chemical reaction
rate of reaction
the change in concentration, per unit time of any one reactant or product
catalyst
a substance that alters the rate of a reaction without itself being used up in the reaction
heterogenous catalysts
the catalyst and the reactants are in different phases
homogenous catalysts
the catalyst and the reactants are in the same phase
autocatalysis
the catalyst is a product of the reaction
activation energy
the minimum amount of energy colliding molecules must have in order for a reaction to take place
pH
minus log to the base 10 of the hydrogen ion concentration (where the hydrogen ion concentration is expressed in mol per litre)
indicator
a substance that changes colour depending on the pH of the solution in which it is placed
hard water
water that does not form a lather easily with soap
temporary hardness
hardness that can be removed by boiling, caused by calcium and magnesium hydrogencarbonates
permanent hardness
hardness that cannot be removed by boiling, caused by calcium and magnesium sulphates
biochemical oxygen demand
the amount of dissolved oxygen consumed by biochemical action when a sample of water was kept in the dark for 5 days at 20 deg celsius
