chemistry
Relative atomic mass
Definition: The average mass of an atom of an element relative to 1/12 the mass of a carbon-12 atom.
Isotope
Definition: Atoms of the same element with the same number of protons but different numbers of neutrons.
Atomic number/mass number
Definition: Atomic number is the number of protons in the nucleus of an atom. Mass number is the sum of protons and neutrons in the nucleus.
Elements, compounds, mixtures
Definition: Elements are substances made up of only one type of atom. Compounds are substances made up of two or more different elements chemically bonded. Mixtures are combinations of two or more substances that are physically mixed but not chemically bonded.
Mole
Definition: A unit of measurement used in chemistry to express amounts of a substance. One mole is equal to Avogadro's number of atoms, ions, or molecules.
Solution, solute and solvent
Definition: A solution is a homogeneous mixture composed of a solute dissolved in a solvent. The solute is the substance being dissolved, and the solvent is the substance in which the solute is dissolved.
Concordant result
Definition: A result in an experiment that is consistent with other results obtained in the same experiment or with accepted values.
Equivalence Point
Definition: The point in a titration at which the amount of titrant added is stoichiometrically equivalent to the amount of analyte present in the sample.
End point of a titration
Definition: The point in a titration at which an indicator changes color or a measured property of the solution undergoes a sudden change, indicating that the reaction is complete.
Error
Definition: The difference between a measured or calculated value and the true value.
Uncertainty
Definition: The range of values within which the true value of a measurement is estimated to lie.
Accuracy and precision
Definition: Accuracy refers to how close a measured value is to the true value, while precision refers to how close repeated measurements are to each other.
Empirical formula
Definition: The simplest whole number ratio of atoms of each element present in a compound.
Unsaturated hydrocarbon
Definition: A hydrocarbon that contains one or more carbon-carbon double or triple bonds.
Molecular formula
Definition: A chemical formula that indicates the actual number of atoms of each element present in a molecule of a compound.
Skeletal formula
Definition: A simplified organic formula that shows the arrangement of atoms in a molecule without showing all the bonds.
Displayed formula
Definition: A molecular formula that shows all the atoms and bonds in a molecule.
Homologous series
Definition: A series of organic compounds with the same functional group and similar chemical properties, where each successive member differs by a CH2 unit.
Structural isomer (give 3 types)
Definition: Isomers that have the same molecular formula but different structural arrangements.
Types:
Chain isomer: Differ in the arrangement of carbon atoms.
Position isomer: Differ in the position of functional groups or multiple bonds.
Functional group isomer: Differ in the functional groups present.
Stereoisomer
Definition: Isomers that have the same molecular formula and the same structural formula but differ in the arrangement of atoms or groups in space.
Optical isomer
Definition: Stereoisomers that are non-superimposable mirror images of each other.
Chiral centre
Definition: An atom in a molecule that is bonded to four different groups, leading to optical isomerism.
Enantiomer
Definition: One of a pair of optical isomers that are non-superimposable mirror images of each other.
Racemic mixture
Definition: A mixture that contains equal amounts of both enantiomers and therefore does not exhibit optical activity.
Plane polarised light
Definition: Light in which the vibrations occur in a single plane only.
Complete/incomplete combustion
Definition: Complete combustion occurs when a fuel burns in a plentiful supply of oxygen, producing carbon dioxide and water. Incomplete combustion occurs when a fuel burns in a limited supply of oxygen, producing carbon monoxide or carbon, and water.
Initiation/propagation/termination
Definition: Steps involved in the free radical chain reaction.
Initiation: Formation of free radicals.
Propagation: Free radicals react to form new free radicals.
Termination: Free radicals combine to form stable molecules.
Molecular ion peak
Definition: The peak in a mass spectrum corresponding to the molecular ion, which is the ion formed when a molecule loses one electron.
Fragment
Definition: A smaller molecule or ion formed by breaking a larger molecule or ion during mass spectrometry.
Isotopic abundance
Definition: The relative amount of each isotope of an element in a sample.
Gay-Lussac Law
Definition: The pressure of a gas is directly proportional to its absolute temperature when volume is held constant.
Ideal Gas law
Definition: The equation relating the pressure, volume, temperature, and number of moles of an ideal gas: PV = nRT.
Energy level, orbital
Definition: Energy levels are the allowed energies that electrons in an atom can have. Orbitals are regions within an energy level where electrons are most likely to be found.
Aufbau principle
Definition: Electrons fill orbitals starting from the lowest energy level and filling higher energy levels successively.
Pauli Exclusion Principle
Definition: No two electrons in an atom can have the same set of four quantum numbers.
Hund’s rule
Definition: Electrons occupy orbitals of the same energy level in a way that maximizes the number of unpaired electrons.
Noble gas configuration
Definition: Electron configuration that resembles the electron configuration of noble gases, which are chemically stable.
Absorption/emission spectra
Definition: Absorption spectra show the absorption of light at different wavelengths by a substance. Emission spectra show the emission of light at different wavelengths by a substance.
First (second/third) ionisation energy
Definition: The energy required to remove one (two/three) mole(s) of electrons from one mole of atoms in the gaseous state.
Electrophile/nucleophile
Definition: Electrophiles are electron-deficient species that seek electrons. Nucleophiles are electron-rich species that donate electrons.
Heretolytic/homolytic fission
Definition: Homolytic fission involves the breaking of a covalent bond with each bonded atom getting one of the bonded electrons. Heterolytic fission involves the breaking of a covalent bond with one of the bonded atoms getting both of the bonded electrons.
Markovnikiv’s rule
Definition: In addition reactions of unsymmetrical alkenes, the major product is formed by the attachment of the electrophile to the carbon atom with fewer hydrogen atoms attached.
Polymer
Definition: A large molecule composed of repeating structural units, or monomers.
Ionic/covalent/metallic bond
Definition:
Ionic bond: Formed by the electrostatic attraction between oppositely charged ions.
Covalent bond: Formed by the sharing of electrons between atoms.
Metallic bond: Formed by the delocalization of electrons in a metal lattice.
Cation/anion
Definition: Cations are positively charged ions formed by the loss of electrons. Anions are negatively charged ions formed by the gain of electrons.
Sigma/pi bond
Definition: Sigma bonds are formed by the head-to-head overlap of atomic orbitals. Pi bonds are formed by the side-to-side overlap of atomic orbitals.
Coordinate/dative covalent bond
Definition: A covalent bond in which both electrons are provided by one atom.
Electronegativity
Definition: The ability of an atom to attract bonding electrons towards itself in a covalent bond.
Dipole
Definition: A separation of charge within a molecule, leading to a partially positive end and a partially negative end.
Van der Waals
Definition: Weak intermolecular forces between molecules, including London dispersion forces, dipole-dipole interactions, and hydrogen bonds.
Dipole-dipole forces
Definition: Intermolecular forces between polar molecules.
Hydrogen bonds
Definition: Strong dipole-dipole attractions between molecules containing hydrogen bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine.
Tetrahedral/octahedral etc
Definition: Geometric arrangements of atoms or groups of atoms around a central atom in a molecule.
Lewis acid/base
Definition:
Lewis acid: Electron pair acceptor.
Lewis base: Electron pair donor.
Bronsted-Lowry acid/base
Definition:
Bronsted-Lowry acid: Proton (H+) donor.
Bronsted-Lowry base: Proton (H+) acceptor.
Oxidising/reducing agent
Definition:
Oxidising agent: Substance that gains electrons and is reduced in a redox reaction.
Reducing agent: Substance that loses electrons and is oxidized in a redox reaction.
Alkoxide
Definition: A negatively charged ion formed by deprotonation of an alcohol.
Primary/secondary/tertiary
Definition: Terms used to describe the number of carbon atoms bonded to the carbon atom directly attached to a functional group.
Primary: One carbon attached.
Secondary: Two carbons attached.
Tertiary: Three carbons attached.
CFCs
Definition: Chlorofluorocarbons, a class of compounds formerly used as refrigerants, solvents, and propellants, but phased out due to their role in ozone depletion.
Oxidation/reduction
Definition: Oxidation is the loss of electrons, while reduction is the gain of electrons.
Redox reaction
Definition: A chemical reaction involving the transfer of electrons from one substance to another.
Oxidation state
Definition: A measure of the degree of oxidation of an atom in a chemical compound.
Disproportionation
Definition: A redox reaction in which the same element is both oxidized and reduced.
Carbonyl group
Definition: A functional group consisting of a carbon atom doubly bonded to an oxygen atom.
Fehling’s solution/Tollen’s reagent
Definition:
Fehling’s solution: A blue alkaline solution used to test for the presence of reducing sugars.
Tollen’s reagent: A colorless solution of silver ions complexed with ammonia used to test for the presence of aldehydes.
Giant covalent structure
Definition: A network of atoms held together by covalent bonds extending throughout the structure.
Giant ionic structure
Definition: A three-dimensional arrangement of positive and negative ions held together by strong electrostatic forces.
Polarising
Definition: The ability of an ion to distort the electron cloud of another ion.
Polarisable
Definition: The ability of an ion to be distorted by another ion.
Displacement reaction
Definition: A reaction in which one element displaces another from a compound.
Enthalpy and enthalpy change
Definition: Enthalpy is a measure of the total energy of a system. Enthalpy change is the heat energy transferred in a reaction at constant pressure.
Endothermic and exothermic
Definition:
Endothermic: A reaction that absorbs heat from the surroundings.
Exothermic: A reaction that releases heat to the surroundings.
Standard enthalpy change
Definition: The enthalpy change when reactants in their standard states react to form products in their standard states.
Standard conditions
Definition: Conditions of 298 K and 1 atm pressure.
Hess’s law
Definition: The total enthalpy change for a reaction is independent of the route taken, provided the initial and final conditions are the same.
Enthalpy change of reaction, combustion, formation, neutralisation, atomisation, ionisation, electron affinity, lattice
Definition: Specific types of enthalpy changes associated with different chemical processes.
Enthalpy change of hydration and solution
Definition: Enthalpy changes when ions dissolve in water.
Mean bond enthalpy
Definition: The average energy required to break a specific type of bond in one mole of gaseous molecules.
Arene
Definition: A compound containing one or more benzene rings.
Kekule structure
Definition: A structural formula in which the six carbon atoms of benzene are arranged in a hexagon with alternating single and double bonds.
Delocalised
Definition: Electrons are spread over more than two atoms, typically in a π bond.
Covalent character
Definition: The extent to which a bond between two atoms shares electron density.
Transition metal
Definition: An element located in the d-block of the periodic table.
Heterogeneous/homogeneous catalyst
Definition:
Heterogeneous catalyst: A catalyst that exists in a different phase from the reactants.
Homogeneous catalyst: A catalyst that exists in the same phase as the reactants.
Transition metal complex
Definition: A compound containing a central metal ion bonded to ligands.
Ligand
Definition: A molecule or ion that donates a pair of electrons to a central metal ion.
Coordination number
Definition: The number of donor atoms attached to the central metal ion in a coordination complex.
Geometry
Definition: The arrangement of atoms or groups of atoms around a central atom in a molecule.
Unidentate/bidentate/multidentate
Definition: Terms used to describe ligands based on the number of donor atoms they possess.
Unidentate: Ligands with one donor atom.
Bidentate: Ligands with two donor atoms.
Multidentate: Ligands with more than two donor atoms.
Entropy
Definition: A measure of the disorder or randomness of a system.
Chelate effect
Definition: The increase in stability of a metal complex due to the formation of a ring of atoms.
Hydrolysis
Definition: A chemical reaction in which a molecule reacts with water, resulting in the breaking of a chemical bond.
Esterification
Definition: The reaction of an alcohol with a carboxylic acid to form an ester and water.
Quaternary amine salt
Definition: A salt formed by the reaction of a quaternary amine with an acid.
Diazonium ion
Definition: A positively charged ion containing a nitrogen atom with a positive charge and two attached substituents.
Azo-dye
Definition: A dye containing one or more azo groups (-N=N-).
Hoffman degradation
Definition: A reaction in which an amine is converted into an alkane by treatment with excess halogen and alkali.
SN1 and SN2 reactions
Definition: Types of nucleophilic substitution reactions.
SN1: A two-step reaction involving the formation of a carbocation intermediate.
SN2: A one-step reaction in which the nucleophile attacks the substrate at the same time as the leaving group departs.
SEAR reactions
Definition: Single electron transfer-aromatic substitution reactions.
Enantiopure
Definition: A compound that contains only one enantiomer and no racemic mixture.
Essential amino acid
Definition: An amino acid that cannot be synthesized by the body and must be obtained from the diet.
Optically active compound
Definition: A compound that rotates the plane of polarized light.
Zwitterion
Definition: A molecule with both a positive and a negative electrical charge.
Amphoteric
Definition: A substance that can act as both an acid and a base.
Isoelectric point
Definition: The pH at which a molecule carries no net electric charge.
Buffer
Definition: A solution that resists changes in pH when small amounts of acid or base are added.
Polypeptide
Definition: A polymer consisting of a chain of amino acids linked by peptide bonds.
Protein
Definition: A large biomolecule consisting of one or more polypeptide chains folded into a specific three-dimensional structure.
Optimum temperature/pH
Definition: The temperature or pH at which a reaction or process occurs most efficiently.
Dynamic equilibrium
Definition: A state in which the rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations of reactants and products remain constant over time.
Closed system
Definition: A system in which neither matter nor energy can enter or leave.
Position of equilibrium
Definition: The relative concentrations of reactants and products at equilibrium.
Le Chatelier's principle
Definition: If a system at equilibrium is disturbed by a change in temperature, pressure, or concentration, the system will shift its position of equilibrium to counteract the change.
Catalyst
Definition: A substance that increases the rate of a chemical reaction without being consumed in the process.
Equilibrium constant (Kc, Kp, Ksp, Kd, Ka)
Definition: The ratio of the concentrations of products to reactants at equilibrium, with each concentration raised to the power of its coefficient in the balanced chemical equation.
Common ion effect
Definition: The suppression of the ionization of a weak electrolyte by the presence of a strong electrolyte that has a common ion.
Partial pressure
Definition: The pressure exerted by one component of a gas mixture.
Mole fraction
Definition: The ratio of the number of moles of a component in a mixture to the total number of moles of all components in the mixture.
Rate of reaction
Definition: The change in concentration of reactants or products per unit time.
Collision theory
Definition: The theory that chemical reactions occur when particles collide with sufficient energy and proper orientation.
Activation energy
Definition: The minimum amount of energy required for a reaction to occur.
Maxwell-Boltzmann distribution
Definition: The distribution of speeds of molecules in a gas at a given temperature.
Enzyme/ substrate
Definition: Enzymes are biological catalysts that speed up chemical reactions. Substrates are the molecules upon which enzymes act.
Active site
Definition: The region of an enzyme where the substrate binds and the chemical reaction occurs.
Inhibition
Definition: The process by which a molecule binds to an enzyme and decreases its activity.
Rate equation
Definition: An equation that relates the rate of a chemical reaction to the concentrations of reactants.
Rate constant
Definition: The proportionality constant in the rate equation that relates the rate of a reaction to the concentrations of reactants.
Order of reaction
Definition: The exponent of the concentration term in the rate equation.
Conjugate pair
Definition: A pair of acids or bases that differ by one proton.
Strong acid/base
Definition: An acid or base that completely dissociates in solution to produce ions.
Weak acid/base
Definition: An acid or base that only partially dissociates in solution to produce ions.
pH scale
Definition: A scale used to specify the acidity or basicity of a solution.
pKa
Definition: The negative logarithm of the acid dissociation constant (Ka) of a solution.
Kw – self ionisation of water
Definition: The equilibrium constant for the autoionization of water: Kw = [H+][OH-].
Spectroscopy
Definition: The study of the interaction between matter and electromagnetic radiation.
Fingerprint region
Definition: The region of an infrared spectrum below 1500 cm^-1, which contains unique absorption bands for a particular molecule.
Transmittance
Definition: The ratio of the intensity of light transmitted through a sample to the intensity of light incident on the sample.
Wavenumber
Definition: The reciprocal of the wavelength of a wave, often used as a unit of frequency in spectroscopy.
Absorption coefficient
Definition: A measure of the ability of a substance to absorb radiation.
Pathlength
Definition: The distance traveled by radiation through a sample.
Carbon/proton environment
Definition: The local chemical environment around a carbon or proton atom in a molecule, which influences its chemical shift in NMR spectroscopy.
Chemical shift
Definition: The displacement of a peak in an NMR spectrum from the reference peak, measured in parts per million (ppm).
Integral
Definition: The area under a peak in an NMR spectrum, proportional to the number of protons contributing to the peak.
Splitting
Definition: The division of an NMR peak into multiple peaks, caused by the magnetic interactions between neighboring protons