AS Level Chemistry Definitions

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Acid
Release H⁺ ions when they are dissolved in water. Referred to as proton donors
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Activation Energy
An atom of the same element with a different number of neutrons and mass number
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Addition Reaction
A reactant is added to an unsaturated molecule to make one saturated molecule
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Alicyclic
Contain carbon atoms joined together in a ring that is not aromatic
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Aliphatic
Contain carbon atoms joined together in straight or branched chains
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Alkali
Bases that dissolve in water releasing OH⁻ ions
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Anion
A negatively charged ion
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Aromatic
Unsaturated hydrocarbons that contain a benzene ring
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Average bond enthalpy
The average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species
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Base
Accept H⁺ ions and are referred to as proton acceptors
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Carbocation
An ion that contains a positively charged carbon atom
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Catalyst
A substance that increases the rate of reaction without being used up in the process; provide an alternative pathway for the reaction to take place with lower activation energy
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Cation
A positively charged ion
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Covalent bond
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
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Dative covalent bond
A shared pair of electrons in which both bonded electrons are contributed by one of the atoms in the bond
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Displayed formula
A formula showing the positions of atoms in a molecule and the bonds between them
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Disproportionation
The simultaneous reduction and oxidation of the same element
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Electronegativity
The ability of an atom to attract the bonding electrons in the covalent bond
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Electrophile
Electron pair acceptors
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Electrophilic Addition
An addition reaction in which an electrophile attacks a region of high electron density
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Elimination Reaction
A molecule loses a small molecule
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Empirical formula
Simplest whole number ratio of atoms of each element present in a compound
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Endothermic reaction
Chemicals gain energy from the surroundings, H is positive
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Exothermic reaction
Chemicals lose energy to the surroundings, H is negative
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Enthalpy (H)
The heat energy stored in a chemical system
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Enthalpy change ( H)
The heat energy change measured under conditions of constant pressure
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Functional group
The group of atoms responsible for the characteristic reactions of a compound
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General formula
The simplest algebraic formula of a member of a homologous series
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Heterogeneous catalyst
A catalyst in a different state from the reactants
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Homogeneous catalyst
A catalyst in the same state as the reactants
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Heterolytic fission
A covalent bond is broken with one of the bonded atoms receiving both electrons from the bonded pair, forming two oppositely charged ions
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Homolytic fission
A covalent bond is broken with each bonding atom receiving one electron from the bonded pair to form two radicals
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Homologous series
A series of organic compounds having the same functional group but with each successive member differing by CH₂
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Hydrolysis
A reaction where a substance is split up using water molecules or hydroxide ions
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Intermolecular forces
The weak attractive forces between molecules
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Ionic bond
An electrostatic attraction between ions of opposite charge
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Isomerism
When two or more organic molecules have the same molecular formula but different arrangement of atoms
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Isotope
Atoms of the same element with different numbers of neutrons and different masses
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Le Chatelier's Principle
When a system is in dynamic equilibrium is subjected to change in conditions, the equilibrium position shifts to minimise the change
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Molecular formula
The actual number and type of atoms of each element in a molecule of a compound
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Neutralisation
The reaction between an acid and a base to produce a salt
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Nucleophile
A species that donates a pair of electrons
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Nucleophilic Substitution
A reaction in which a nucleophile is attracted to an electron-deficient carbon atom and replaces an atom or group of atoms on that carbon
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Orbital
A region around the nucleus that can hold up to 2 electrons with opposite spins
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Oxidising agent
A substance that removes electrons from other species and gains electrons itself
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Polar bond
A covalent bond between atoms with different electronegativities with postive and negative partial charges on the bonded atoms
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Radical
A very reactive species with an unpaired electron
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Reducing agent
A substance that adds electrons to other species and loses electrons itself
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Relative atomic mass
The weighted mean mass of an atom of an element compared with 1/12th of the mass of an atom of carbon-12
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Relative formula mass
The weighted mean mass of a formula unit of a compound compared with 1/12th of the mass of an atom of carbon-12
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Relative isotopic mass
The mass of an atom of an isotope compared with 1/12th of the mass of an atom of carbon-12
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Saturated hydrocarbon
Contains single carbon-carbon bonds only
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Skeletal formula
A simplified organic formula shown by removing H atoms from alkyl chains, leaving just a carbon skeleton and functional groups
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Standard enthalpy change of reaction
The enthalpy change that accompanies a reaction in the molar quanities shown in a chemical equation under standard conditions, with all reactants and products in their standard states
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Standard enthalpy change of formation
The enthalpy change when one mole of a compound is formed from its elements in their standard states, under standard conditions
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Standard enthalpy change of combustion
The enthalpy change when one mole of a compound is completely burnt in oxygen under standard conditions
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Standard enthalpy change of neutralisation
The energy change that accompanies the reaction of an acid and a base to form one mole of water, under standard conditions, with all reactants and products in standard states
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Stereoisomers
Have the same structural formula but different arrangement of atoms in space
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Structural formula
The minimal detail that shows the arrangement of atoms in a molecule
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Structural isomerism
Compounds with the same molecular formula but different structural formula
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Substitution reaction
An atom or group of atoms exchanges with a different atom or group of atoms
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Unsaturated hydrocarbon
Contains at least one multiple bond
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-bond (pi bond)
A bond caused by sideways overlap of adjacent p-orbitals above and below the bonding atoms
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-bond (sigma bond)
A bond caused by orbital overlap directly between the bonding atoms
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Other cards in this set

Card 2

Front

An atom of the same element with a different number of neutrons and mass number

Back

Activation Energy

Card 3

Front

A reactant is added to an unsaturated molecule to make one saturated molecule

Back

Preview of the back of card 3

Card 4

Front

Contain carbon atoms joined together in a ring that is not aromatic

Back

Preview of the back of card 4

Card 5

Front

Contain carbon atoms joined together in straight or branched chains

Back

Preview of the back of card 5
View more cards

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