Chemistry Definitions

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Activation Energy

Back 1

Minimum energy required for a collision to be successful

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Addition Polymerisation

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Combination of a large number of monomers to form a single chain

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Addition

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Combination of two or more molecules to form a single molecule

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Atomic Number

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The number of protons in the nucleus of the atom

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Avogadro's number

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The number of elementary particles that there are in 12,000 grams of carbon-12

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Biofuel

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A fuel derived or produced from renewable biological sources

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Catalyst

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A substance which increases the rate of a chemical reaction without itself being chemically unchanged at the end of a reaction

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Chain Isomerism

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The same molecular formula but a different arrangement of carbon atoms in the chain

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Collision energy

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Combined kinetic energy of the colliding particles

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Collision frequency

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Number of collisions between particles per second

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Covalent bond

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A pair of electrons shared between two atoms

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Dative covalent bond

Back 12

A pair of electrons shared between two atoms, one of which provides both of the electrons

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d-block element

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An element with s and d-electrons but no p-electrons in its outer shell

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Dynamic equilibrium

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A reaction in which the forward and reverse reaction are proceeding at the same rate, so the concentrations of reactants and products are constant

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Electronegativity

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The ability of an atom to attract electrons towards itself in a covalent bond

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Electrophile

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Species which can accept an electron pair from another species

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Elimination

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Loss of a small molecule from a large molecule to form an unsaturated compound

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Empirical formula

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The simplest whole number ratio in which the atoms of each element in a compound are found

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Endothermic

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A change during which is absorbed by the particles

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Enthalpy change

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Change in heat energy under constant pressure

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Exothermic

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A change during which heat is given out by the particles

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First Ionisation Energy

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The heat energy required to remove one electron from each of a mole of free gaseous atoms of that element

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Free Radical

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Species with an unpaired electron

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Functional Group

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An atom or group of atoms which confer specific physical and chemical properties to the molecule

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Functional Isomerism

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The same molecular formula, but a different functional group

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Geometrical Isomerism

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The same molecular formula, but a different spatial arrangement of atoms around a double bond

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Heterolytic Fission

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Breaking of a covalent bond in such a way that both electrons go to the same atom

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Homologous Series

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Series of compounds with the same functional group in which the molecular formula varies by -CH2- from one member to the next

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Homolytic Fission

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Breaking of a covalent bond in such a way that one electron goes to each atom

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Hydration

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Addition of water to a species

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Hydrolysis

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Use of water to break covalent bonds

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Ionic Bond

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An attraction between oppositely charged ions

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Isomerism

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A number of different structures having the same molecular formula

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Isotopes

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Atoms with the same atomic number but different mass numbers // Atoms with the same number of protons but different numbers of neutrons

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Le Chatelier's principle

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If a change in conditions is imposed on a system at equilibrium, the system will react in such a way as to oppose the effect of that change

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Mass Number

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The total number of protons and neutrons in the nucleus of an atom

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Metallic bond

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Attraction between a cation and a sea of delocalised electrons

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Molar Mass

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The mass of a substance containing the same number of elementary particles as there are in 12.000 grams of carbon-12

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Mole

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The amount of a substance containing the same number of elementary particles as there are in 12.000 grams of carbon-12

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Molecular formula

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The number of atoms of each element in one molecule of the substance

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Nucelophile

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Species which can use a lone pair of electrons to form a covalent bond

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Oxidation Number

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Charge that would be on an atom of the bonding were completely ionic

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Oxidation

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Addition of oxygen or removal of hydrogen or loss of electrons

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Oxidising agent

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Electron acceptor

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p-block element

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An element with p-electrons in its outer shell

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Polar bond

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The existence of partial positive and negative charges on each end of the bond as a result of the unequal sharing of electrons

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Positional Isomerism

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The same molecular formula, but the functional group is in a different position

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Rate of Reaction

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Change in concentration of a species per unit time

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Redox reaction

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Reaction in which electrons are transferred from one species to another

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Reducing agent

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Electron donor

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Reduction

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Gain of electrons, removal of oxygen or addition of hydrogen

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Relative atomic mass

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The ratio of the average mass of an atom to 1/12th of the mass of one atom of carbon-12