Definitions Flashcards
Atomic number
Number of protons in the nucleus of the atom
Mass number
The sum of the number of protons and neutrons in the nucleus of an atom
Nuclear charge
The total charge of all the protons in the nucleus and has the same value as the atomic number
Isotopes
Atoms of the same element with the same number of protons and electrons but a different number of neutrons in the nucleus
Relative atomic mass
Average mass of an atom relative to 1/12th of the mass of an atom of carbon 12
Relative isotopic mass
Average mass of an atom of an isotope relative to 1/12th of the mass of a carbon 12 atom
Relative molecular mass
The average mass of a molecule relative to 1/12 of the mass of an atom of carbon 12
Quantum shells
Electron shells, specify the energy level of an electron
First ionisation energy
The energy required to remove one mole of electrons from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous +1 ions
Second ionisation energy
The energy required to remove 1 mole of electrons from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions
Orbital
A region in an atom that can hold up to two electrons with opposite spins
Periodicity
Trends in element properties with increasing atomic number
Hund’s rule
When electrons fill the orbital as they occupy them singularly before they pair up.
Pauli exclusion principle
Electrons with the same orbital must have opposite spins
Aufbau principle
As the atomic number increases, the electrons are added to the orbitals in order of increasing orbital energy until all electrons are accommodated
Shielding
A decrease in the nuclear charge experience by an outer electrons caused by electron electron repulsion between the outer shell electron and electrons from adjacent quantum shells
Ionic bond
Strong electrostatic forces of attraction between two oppositely charged ions. Strength of attraction depends on the relative sizes and charges of ions
Cation
A positively charged ion
Anion
A negatively charged ion
Isoelectronic species
Chemical species that have the same number of electrons.
Covalent bond
The strong electrostatic attraction between two nuclei and the shared pair of electrons between them.
Sigma bond
A bond that results from a direct overlap of two orbitals
Pi bond
A bond that is formed when two orbitals overlap sideways
Dative covalent bond
Occurs when one atom donates both electrons in a bond
Allotropes
Different forms of the same element. E.g. diamond graphite graphene
Malleable
A substance can be shaped
Ductile
A substance can be drawn into wires
Intermolecular forces
Forces between the molecules
Electronegativity
The ability of an atom to attract the bonding electrons in a covalent bond.
Dipole
The difference in charge between the two atoms of a covalent bond caused by a shift in the electron density in the bond due to the electronegativity different between the elements participating in bonding.
Metallic bonding
The electrostatic attraction between the metal ions and the sea of delocalised electrons that surround them
Delocalised electrons
The electrons that are not contained within an single atom or covalent bond
Bond length
Internuclear distance between two covalently bonded atoms
London forces
Weak intermolecular forces arising due to fluctuations of electron density within a non polar molecule. These fluctuations may temporarily cause an instantaneous dipole that can then induce a dipole in another molecule .
Permanent dipole-dipole interactions
Dipole-dipole attractions between polar molecules. Stronger than London forces
Hydrogen bond
An intermolecular force between a hydrogen bonded to a more electronegative atom ( N,O,F)
Oxidation number
The charge of an ion
Oxidation
Loss of electron, increase in oxidation number
Reduction
Gain in electrons, decrease in oxidation number
Redox
A reaction that involves oxidation and reduction
Oxidising agent
Accepts electrons and gets reduced in a redox reaction
Reducing agent
Donates electrons and gets oxidised in a redox reaction
Half equations
A full redox equation could be split into two half equations. Oxidation and reduction.
Disproportionation
A redox reaction involving an element in a single species being simultaneously oxidised and reduced .
Thermal stability
Refers to the extent to which a compound decomposes when subjected to heating
Electronic transition
The movement of electrons between energy levels. When an electron In a ground state absorbs some energy it can move to the excited state. When it moves back to ground state energy is released in a particular wavelength corresponding a specific colour.
Mole
The unit for amount of substance
Avogadro’s constant
The number of atoms in exactly 12g of carbon 12 6.02x10^23
Molar mass
Mass of one mole of the substance expressed in gmol-1
Empirical formula
The smallest whole number ration of atoms of each element in a compound
Molecular formula
The actual number of atoms of each element in a molecule
Spectator ions
Ions that do not take part in the reaction
Hydrate
A compound that has molecules of water of crystallisation
Solution
Standard solution is the one with accurately known concentration
Mass per concentration
Mass of solute per volume of solution
Molar concentration
Moles of solute per volume of solution
Primary standard
A substance used for preparation of a standard solution by weighing
Avogadros law
Provided conditions of temperature and pressure are the same, equal volume of gases contain the same number of molecules
Molar volume
The volume of 1 mole of a gas
Displacement reaction
More reactive element reacts to take the place of a less reaction element in a compound
Precipitation reaction
One take produces an insoluble solid
Error
A discrepancy between the value obtained in the experiment and an actual value
Precision
Refers to how close to each other the values obtained in an experiment are
Accuracy
Refers to how close these values are to the actual value
Concordant results
Results that lie close to each other
Margin error
The range in which the true value of a measurement could lie
Random errors
They occur when conditions are varied in an unpredictable manner
Systematic errors
Errors which are constant when you repeat an experiment, they are usually a result of the apparatus used.
Percentage uncertainty equation
(Uncertainty / reading)x100
Percentage yield
(Actual yield/theoretical yield) x100
Atom economy
Measure of the proportion of reaction atoms that become part of the desired product in the balanced chemical equation
Atom economy equation
(Molar mass of desired/molar mass of total ) x100
Hydrocarbon
A compound exclusively consisting of hydrogen and carbon atoms
Homologous series
Series of organic compounds with the same functional group and general formula
Functional group
A group of atoms responsible for the characteristic reactions of a particular compound
Addition
Joining two or more molecules together to form a larger molecule.
Polymerisation
Chemically combining lots of simple molecules to form a giant molecule
Repeating unit
A simplest pattern of the polymer that upon translation reproduces the whole structure
Elimination
When a small group of atoms breaks away from a larger molecule to form a c=c bond
Substitution
Whenone species is replaced by another
Hydrolysis
Breaking bonds in a molecule by a reaction with water
Dehydration
Reaction in which water is eliminated from a starting material
Saturated
Refers to a compound with all the c-c bonds being single bonds
Heterolytic fission
The process of breaking a covalent bond within a molecule leading to the formation of ions. Upon bond breaking one atom receives the electron pair and becomes negative it charged ion. Other atom becomes a cation
Homolytic fission
The process of breaking down a covalent bond within a molecule leading to the formation of radicals. Upon bond breaking one atom receives one electron from the bonding pair and both atoms become radicals
Radicals
A species with an unpaired electron. Represented in mechanisms by a single dot.
Free radical substitution
Photochemical reaction (requires UV light) between halogens and alkanes to form halogenoalkanes
Stereoisomerism
Occurs when two double bonded carbon atoms each have two different atoms of groups attached to them.
Structural isomerism
Occurs when species have the same molecular formula, but a different structural formula
Saturated hydrocarbons
Hydrocarbons which contain only single bonds between carbon atoms
Unsaturated hydrocarbons
Hydrocarbons which contain at least one carbon-carbon double bond
Cracking
Breaking long chain alkenes into smaller, more useful hydrocarbons. Helps to convert low demand hydrocarbons into more highly demanded ones
Reforming
Processing of straight chain hydrocarbons into branched chain alkanes and cyclic hydrocarbons for efficient combustion.
Knocking
Alkanes explode of their own accord when the fuel/air mixture in an engine is compressed
Complete combustion
Produces fully oxidised products as opposed to incomplete combustion
Catalytic converters
Get rid of pollutants in cars by using platinum catalyst to convert them to harmless gases
Biofuels
Fuels made from living matter over a short period of time
Recycling
Conversion of waste from polymer into other useful materials
Incinerator
A device for converting polymer waste into energy
Feedstock
For conversion of polymer waste into compounds that can be used to synthesise new polymers
Biodegradable
Refers to a polymer that can be decomposed by microbes. Usually has polar groups.
Electrophile
Electrons pair acceptor in an organic mechanism. Attracted to areas with a lot of electrons
Nucleophile
Electron pair donors in an organic mechanism. Attracted to electron-deficient areas.
Electron releasing group
A group that releases the electron towards the atom it is joined to
Carbocation
A carbon atom bearing a positive charge
Markovnikoff’s rule
Weak statement - when adding a hydrogen hankies to an unsymmetrical alkene, the major product is formed from hydrogen adding to the carbon with more hydrogens, and hailed adding to the carbon with fewer hydrogens.
Strong statement - the major product of an electrophilic addition to the unsymmetrical alkene results from a reaction proceeding via most stable carbocationic intermediate.
Distillation with addition
Performing the reaction under distillation conditions whilst adding one of the reagents. The product distills off as it forms in case of oxidation of an alcohol to an aldehyde.
Solvent extraction
A method for separating a compound from a mixture by causing it to move to another solvent
Fractional distillation
A distillation that utilises a fractionating column (packed glass beads that provide a surface for the vapour to condense and evaporate again) used to separate liquids of similar boiling points.
Molecular ion peak
The peak with the highest m/z value. This is the molecular mass of the molecule being tested in the mass spectrometer
[M+1] peak
The Peak which which occurs due to the isotope C13
Fragmentation
When molecular ion is fragmented to smaller molecules / ions
Infrared radiation
Has frequencies below that of red light
Stretching
When a bond absorbs infrared radiation and therefore changes it’s length
Transmittance
A value in the IR spectrum that shows the amount of radiation absorbed at a particular frequency
IR spectroscopy
A technique used to determine the presence of certain functional groups within in the molecules
Mass spectrometry
A technique that gives you information about the mass of a molecule and it’s fragments
Enthalpy change
Heat energy change in a reaction at a constant pressure
Standard conditions
100 kPa, 298K 1moldm-3
Endothermic
Heat absorbed +ve Enthalpy change
Exothermic
Heat given off -ve value of Enthalpy change
Standard Enthalpy change of reaction
Enthalpy change when reaction occurs in the molar quantities shown in the chemical equation under standard conditions.
Standard Enthalpy change of formation
Enthalpy change when 1 mole of a compound in formed from its elements in their standard states under standard conditions
Standard Enthalpy of combustion
Enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions
Standard Enthalpy of neutralisation
Enthalpy change when an acid and alkali react together under standard conditions to form 1 mole of water
Equation for calorimeter calculations
Heat change mcAT
m is mass
c is heat capacity
AT is change in temperature
Specific heat capacity
The amount of energy needed to raise a temperature of 1g of a substance by 1 degree
Hess’s law
The total Enthalpy change is independent of the reaction pathway taken
Bond Enthalpy
Amount of energy required to break 1 mole of the stated bond in the gas phase
Enthalpy change of a reaction equation
Sum of bond enthalpies of reactant - sum of bond enthalpies of products
Mean bond Enthalpy
Average amount of energy needed to break a specific type of bond, measured over a variety of different molecules
Activation energy
The minimum amount of kinetic energy the particles need to react
Catalyst
A substance that proves an alternative reaction route of lower activation energy and hence speeds up the reaction. It is chemically unchanged at the end of the process
Heterogenous catalyst
Catalyst that is in a different phase from the reactants
Homogenous catalyst
Catalyst in the same physical state as reactants.
Maxwell-boltzmann distribution
A distribution of energy among the molecules of a gas in a closed system.
Area under the graph indicates the number of particles.
Features of a dynamic equilibrium
Reversible reaction in a closed system
Forward and backward reactions occur simultaneously
Rate of forward reaction = rate of backwards reaction
There is no net change in concentrations of reactants and products
Homogenous system
A system where all the chemicals are in the same phase
Heterogenous system
A system where not all the chemicals are in the same phase
Le chatelier’s principle
If there’s a small change in concentration, pressure/volume or temperature to a closed system in dynamic equilibrium, the equilibrium will shift to minimise the change.
Contact process
A method of production. The key step involves the conversion of SO2 to SO3 in presence of oxygen, catalysed by V2O5.
Mole fraction of gas
Number of moles of particular gas / total number of moles of all gases in the mixture
Partial pressure
The pressure exerted by a particular gas in a mixture in a closed system. Relation to mole fraction: mole fraction x total pressure = partial pressure
Total pressure
Sum of all partial pressures
Reaction quotient vs Kc, Kp
The reaction quotient is the same as the equilibrium constant at equilibrium
Brønsted-Lowry acid
A proton donor
Brønsted-Lowry base
A proton acceptor
Conjugate acid/base pair
Two species that differ by H+.
Acid loses hydrogen becomes base
Base gains hydrogen becomes acid
pH
A figure expressing the acidity or alkalinity of a solution on a logarithmic scale.
7 is neutral
<7 is acidic
>7 alkali
Equation to work out pH
pH = -log[H+]
Ka
The acidic dissociation constant
Equation for pKa
pKa = -log[Ka]
The lower the value the stronger the acid
Kw
The ionic product of water
Equation of pKw
pKw = -log[Kw]
Lewis acid
Electron pair acceptor
Lewis base
Electron pair donor
Strong acid
Acid which completely dissociates in water
Strong base
Base which completely dissociates in water
Weak acid
Acid which dissociates only slightly in water
Weak base
Base which is only slightly protonated in water
Amphoteric
Refers to a substance that can act as an acid of base
Monoprotic acid
Can release only one H+ upon dissociation
Polyprotic acid
Can release more than one H+ upon dissociation
Equivalence point
The point when full neutralisation occurs
End point
The point during the titration when the indicator changes the colour.
Buffer
A solution which resists change in pH when small amount of strong acid/base are added
Acidic buffer
A buffer containing a weak acid and its conjugate base
Alkaline buffer
A buffer containing a weak base and its conjugate acid
Standard lattice energy
Energy change when 1 mole of an ionic solid is formed from its constituent gaseous ions under standard conditions
Standard Enthalpy of atomisation
Enthalpy change when 1 mole of gaseous atoms is formed from the elements in its standard size. Always endothermic
First electron affinity
The Enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
Enthalpy change of hydration
The Enthalpy change when one mole of a gaseous ion is completely dissolved in water under standard conditions
Enthalpy change of solution
Enthalpy change when 1 mole of ionic solid completely dissolves in water under standard conditions to form an infinitely diluted solution
Polarisation
Distortion of a charge distribute.
Entropy
A measure of the disorder of a system.
A reaction that produces the greater number of molecules than the number of reactants molecules Will have a positive entropy change as there will exist more random arrangements of these molecules. I.e the system becomes more disordered.
Gibbs free energy
A measure of feasibility of a chemical reaction.
Anode
Positive electrode ( oxidation )
Cathode
Negative electrode (reduction)
Standard hydrogen electrode
A platinum foil immersed in 1 mol do -3 HCl enclosed in a tube containing hydrogen gas at standard pressure.
Standard cell potential
Voltage measured under standard conditions when a half cell is connected to a standard hydrogen electrode. Tells you how readily a substance releases electrons relative to H2
Salt bridge
A porous substance soaked with a solution of an inert strong electrolyte. The salt ions flow through the bridge to complete the cell and balance charges in a solution
Electrochemical cell
Produces electricity from a chemical reaction
Storage cell
A cell that can be recharged when the current is passed in the opposite way to the current generated by a chemical reaction in the cell
Fuel cell
A cell used to harness electricity from a chemical reaction. Chemicals are stored separately outside the cell and fed in when electricity is required.
Transition metals
d-block elements that form one or more stable ions with incompletely filled d orbitals
Complex ion
A central metal cation surrounded by Ligands
Ligand
Atom, ion or molecule that donates a pair of electrons to a central metal ion
Cisplatin
Pt(NH3)2Cl2 with cis geometry. An anticancer compound that binds the two strands of DNA during the cell division process. This prevents them from separating and hence stops the cell division.
Denticity
Describes how many dative bonds a ligand can form.
Coordination number
Number of dative covalent bonds that ligands form with the central metal ion.
Ligand exchange
A reaction in which a ligand is substituted by another ligand
Adsorption
The process of forming weak bonds by reactants to a surface of a solid catalyst.
Desorption
The reverse process to adsorption. Adsorbed molecules leave the surface.
Autocatalysis
When a product catalyses the reaction.
Haemoglobin
A protein responsible for oxygen transport in human blood. Contains Fe2+ sure. 4 Haem groups bond to iron in square planar fashion via coordinate bonds. Fifth bond is made from protein bond and iron centre.
Rate of reaction
Change in concentration of substance per unit of time
Rate equation
Describes the relationship between the rate of chemical reaction and the concentration/pressure of reagents.
Rate constant
Relates the rate of a chemical reaction at a given temperature to the product of the concentrations of reactants
Orders or a reaction
Tells you how the reactants concentration will affect the rate of reaction.
Overall order of reaction
Sum of all the individual orders of all reactants in a chemical reaction
Half life
Time taken for the initial amount of reactant to decrease by half
Rate determining step
The slowest step in a multistep reaction. The overall rate is decided by this step
Instantaneous rate
A rate found by drawing the tangent to the line of concentrate vs time graph and calculating the gradient of it
CFCS
Chlorofluorocarbons. Contribute to the depletion of ozone layer. UV light can break down the C-Cl bond and form a chlorine radical.
Colorimeter
Device for measuring absorbance
Absorbance
Amount of light absorbed by the solution
Chiral centre
A carbon atom bearing four different substituents
Chirality
When a compound and its mirror image are non-superimposable
Plane-polarised light
Monochromatic light that oscillates in only one plane
Polarimeter
A device for measuring an angle rotation caused by a chemical.
Enantiomers
Optical isomers that are mirror images of each other . They rotate the plane of polarisation of plane polarised light
Optical activity
The ability of a single optical isomer to rotate the plane of polarisation of plane-polarised monochromatic light. An optically active molecule has no planes of symmetry
Racemic mixture
An equimolar mixture of enantiomers of a chiral compound. Doesn’t rotate plane of polarised light as the two enantiomers cancel out each others light rotating effect. Racemic mixtures are split 50/50
Dimer
A molecule consisting of two identical molecules linked together
Esterification
Reaction of an alcohol with a carboxylic acid in the presence of an acid catalyst to form an ester
Condensation polymerisation
A reaction in which monomers link together to form a large molecule with the additional formation of small molecule.
Saponification
Refers to the process of making soap. It is a basic hydrolysis of long chain triglycerides to glycerol and corresponding salts of carboxylic acids.
Tollen’s test
A test that differentiates between aldehydes and ketone. Aldehydes undergo oxidation easily. Ketones do not. Aldehydes reduce tollen’s agent to metallic silver where a mirror can be observed. Ketones do not.
Fehling’s and Benedict’s test
Test argent is a Cu2+ complex. Aldehyde will undergo a redox reaction to reduce the deep blue copper complex to brick red precipitate.
Brady’s reagent
2,4-dinitrophenylhydrazine. Used for testing for presence of a carbonyl group. Positive result of bright orange precipitate.
Iodoform reaction
Used for identification of ethanol, ethanal, methyl ketones and secondary alcohols. Involved warming the compound with iodine and alkaline solution. Positive result is appearance of a yellow crystalline precipitate and characteristic smell.
Aromatic
Refers to a hydrocarbon ring having delocalised electrons in the pi - framework. Called arenes
Kekule model
Benzene is made up of planar ring six carbon atoms with alternating single and double bonds between them
Delocalised model
Two ring shaped electron clouds above and below the plane of six carbon atoms due to the presence of entente pi-framework arising from the overlap of six p orbitals
Delocalisation energy
Extra stability gained from the delocalised pi-system in benzene
Halogen carrier
A catalyst (Lewis acid) which helps to introduce the halogen to the aromatic ring by rendering the formation of the electrophile.
Amines
Derivatives of ammonia, consecutive hydrogens are replaced by a carbon group.
Basicity
Refers to the extent to which a basic molecule can donate its electron pair to a proton/hydrogen or a water molecule
Amino acid
Organic compounds containing a carboxylic acid group and an amine group
Zwitterion
A molecule that contains a positively charged site and a negatively charged site, the overall charge being zero.
