Read each term where it’s used
In Augment’s notes, a marked term shows its definition when you hover or tap it, and each page ends with the terms it introduces.
In Augment’s notes, a marked term shows its definition when you hover or tap it, and each page ends with the terms it introduces.
131 terms from Models of bonding and structure, each defined in a sentence or two, with the part of the syllabus where you first meet it. 34 of them are HL only, and marked.
A polymer formed by addition polymerization of monomers with a C=C double bond, such as poly(ethene), PVC and PTFE.
A reaction in which many monomers containing a C=C double bond join into one long saturated chain, with no other product, so the atom economy is 100 %.
One of two or more structural forms of the same element in the same physical state, such as diamond, graphite, graphene and fullerenes for carbon; allotropes differ in bonding and so in properties.
A mixture of a metal with one or more other elements (usually metals), made by melting them together; different-sized atoms disrupt the layers, so alloys are usually harder than the pure metal.
The group that joins the residues of an acid and an amine in an amide or a polyamide.
An organic molecule with both an amino group () and a carboxyl group (); amino acids are the monomers of proteins.
The molar mass of the desired product as a percentage of the total molar mass of all the reactants in the balanced equation; it measures how much of the reactants' mass can end up in the desired product.
The mean of the electronegativities of two bonded elements, ; on the bonding triangle a low value indicates metallic bonding and a high value covalent bonding.
One of the two positions on the vertical axis of a trigonal bipyramid, 180° apart, each with three neighbouring electron domains at 90°.
An ionic compound of only two elements, a metal and a non-metal, named with the cation first and the anion ending in "-ide", such as sodium chloride.
Able to be broken down into simpler substances by microorganisms in the environment.
The angle between two bonds from the same central atom, such as 104.5° for H–O–H in water.
The straight line joining the nuclei of two bonded atoms.
The separation of charge along a polar covalent bond, shown with partial charges or with an arrow pointing to the atom.
The energy needed to break one mole of a particular covalent bond in gaseous molecules to form gaseous atoms; always positive.
The distance between the nuclei of two covalently bonded atoms; more shared pairs between the same two atoms give a shorter bond.
The number of shared electron pairs between two bonded atoms (1 single, 2 double, 3 triple); in a resonance hybrid it can be fractional, such as 1.5 in benzene.
The idea that bonding changes gradually from covalent, through polar covalent, to ionic (and from covalent to metallic) rather than falling into separate categories; most real bonds have mixed character.
A pair of electrons shared between two atoms in a covalent bond.
A triangular diagram (in the data booklet) that classifies the bonding in an element or binary compound as ionic, polar covalent, covalent or metallic by plotting the electronegativity difference of its two elements against their average electronegativity.
Breaking or shattering when struck rather than bending; ionic solids are brittle because a shifted layer brings ions of the same charge together and they repel.
The charge of an ion relative to its size; small, highly charged ions have a high charge density and attract electrons or other ions strongly.
An arrangement of equal spheres, such as the atoms of many metals, that leaves the least empty space; each atom has twelve nearest neighbours.
A material made of two or more distinct materials that stay separate within it, combining their properties, such as reinforced concrete or fibreglass.
A polymer formed by condensation reactions between monomers that each have two functional groups, with a small molecule (usually water or hydrogen chloride) released as each link forms.
A reaction in which two molecules join to form a larger molecule with the release of a small molecule such as water or hydrogen chloride.
A bond drawn through the bracket at each end of a repeating unit, showing where the unit joins the next one in the polymer chain.
A covalent bond in which both electrons of the shared pair come from the same atom, as in the fourth N–H bond of .
In a lattice, the number of nearest neighbours of opposite charge around an ion (six in sodium chloride); in a complex ion, the number of coordination bonds to the central ion.
The electrostatic attraction between a shared pair of electrons and the positively charged nuclei of the two bonded atoms.
A lattice of atoms joined by covalent bonds throughout, with no separate molecules, as in diamond, silicon and silicon dioxide.
A covalent bond joining two neighbouring polymer chains; cross-links make a polymer more rigid and stop it softening on heating.
The spreading of electrons over three or more atoms, so that they are not confined to one bond or one atom; delocalized pi electrons form where p orbitals on adjacent atoms overlap sideways.
The extra stability of a species with delocalized electrons compared with one localized structure; for benzene about , from enthalpies of hydrogenation.
An electron that is not attached to one atom or bond but is shared by many atoms and free to move through a structure, as in metals, graphite and benzene.
An allotrope of carbon in which each atom is covalently bonded to four others tetrahedrally in a three-dimensional network; very hard and does not conduct electricity.
The molecule formed when two amino acids join by a condensation reaction, linked by a peptide (amide) link, with the release of water.
A measure of the separation of positive and negative charge in a molecule; a molecule whose bond dipoles do not cancel has a net dipole moment.
An attraction between the permanent dipole of a polar molecule and the dipole it induces in a neighbouring non-polar particle.
An attraction between the permanent dipoles of neighbouring polar molecules.
A covalent bond made of two shared pairs of electrons; shorter and stronger than a single bond between the same atoms.
Able to be drawn out into a wire without breaking, a typical property of metals.
The ability of a substance to carry an electric current, which needs mobile charged particles: delocalized electrons in metals and graphite, mobile ions in molten or dissolved ionic compounds.
The decomposition of a molten or dissolved ionic compound (an electrolyte) by a direct electric current, with ions gaining or losing electrons at the electrodes.
A substance that conducts electricity when molten or in aqueous solution, because it contains mobile ions, and is decomposed by the current.
A region of electron density around a central atom: a lone pair, a single bond or a multiple bond each count as one domain.
The arrangement of all the electron domains, bonding and non-bonding, around a central atom: linear, trigonal planar or tetrahedral for two, three or four domains.
A measure of the ability of an atom to attract a shared pair of electrons in a covalent bond; it has no units (Pauling scale).
The difference between the electronegativities of two bonded elements, ; the larger it is, the greater the ionic character of the bond.
A reaction in which an electrophile replaces an atom (usually hydrogen) on an aromatic ring, through a carbocation intermediate, the ring keeping its delocalized π system; for example the nitration of benzene.
The enthalpy change when hydrogen adds to the double bonds of one mole of an unsaturated compound to give the saturated compound, for example about for cyclohexene.
One of the three positions around the middle of a trigonal bipyramid, at 120° to each other; lone pairs occupy these positions because they have only two neighbouring domains at 90°.
The group that joins the residues of an acid and an alcohol in an ester or a polyester.
A valence shell with more than eight electrons around a central atom, as in (10) and (12); possible only for atoms of period 3 and beyond.
The minimum energy needed to remove one mole of electrons from one mole of gaseous atoms in their ground state, , in .
The charge an atom in a Lewis formula would have if all bonding pairs were shared equally: (valence electrons minus lone-pair electrons minus half the bonding electrons).
A molecular allotrope of carbon made of closed cages of carbon atoms, such as ; the molecules are held together only by London forces.
A single layer of graphite, one atom thick: a very strong, light, flexible sheet that conducts electricity and heat well.
An allotrope of carbon made of layers of hexagonal rings, each atom bonded to three others with one delocalized electron; the layers are held by London forces, so it is soft and conducts electricity.
One of a set of equivalent orbitals formed by mixing s and p orbitals on an atom; each has one large lobe pointing in a definite direction.
The mixing of atomic orbitals on one atom to form an equal number of new, equivalent hybrid orbitals used to form sigma bonds and hold lone pairs.
An ion surrounded by water molecules attracted to it: the oxygen atoms face a cation and the hydrogen atoms face an anion.
An attraction between a hydrogen atom covalently bonded to N, O or F and a lone pair on an N, O or F atom of a neighbouring molecule; the strongest intermolecular force.
A central atom with fewer than eight valence electrons in a molecule, as for Be in (four) and B in (six).
A dipole created in an atom or molecule when a nearby dipole distorts its electron cloud.
An alloy in which much smaller atoms of the added element occupy the spaces between the metal atoms, as carbon does in steel.
The electrostatic attraction between oppositely charged ions.
A compound made of cations and anions held together by ionic bonding in a giant lattice, typically formed between a metal and a non-metal.
A giant three-dimensional regular arrangement of alternating cations and anions, each surrounded by ions of the opposite charge and held by non-directional electrostatic attraction.
The radius of an ion; cations are smaller than their atoms and anions are larger than their atoms.
A structure of benzene as a six-membered ring of carbon atoms with alternating single and double bonds; it describes one resonance structure, not the real molecule.
The standard enthalpy change when one mole of a solid ionic compound is separated into its gaseous ions, e.g. ; it is positive and measures the strength of the ionic bonding.
A diagram of a covalently bonded species that shows all its valence electrons: bonding pairs between the atoms and lone pairs on the atom that owns them, as dots, crosses or lines.
A molecule or ion with a lone pair of electrons that forms a coordination bond to a central metal ion, such as , , or .
An attraction between a temporary dipole and the dipole it induces in a neighbouring particle; it acts between all molecules and increases with the number of electrons and the contact area.
A pair of valence electrons that belongs to one atom only and is not shared in a bond.
The shine of a freshly cut or polished metal surface, which reflects most visible light falling on it.
A very large molecule containing thousands of atoms or more, such as a polymer, a protein or DNA.
Able to be hammered or pressed into a new shape without breaking; metals are malleable because their non-directional bonding lets layers of cations slide.
The electrostatic attraction between a lattice of positive metal ions (cations) and delocalized electrons.
The regular, closely packed three-dimensional arrangement of cations in a metal, surrounded by a sea of delocalized electrons.
A fragment of plastic less than 5 mm across, formed when larger plastic items break up or made deliberately small; microplastics persist in oceans, soils and organisms.
The arrangement of the atoms (not the lone pairs) around a central atom, such as bent, trigonal pyramidal or tetrahedral.
A small molecule that joins with many others of the same kind (or of a second kind) to form a polymer.
A polymer made by living organisms, such as starch, cellulose, proteins, DNA and natural rubber.
An electron configuration the same as that of a noble gas, with a full outer level (eight electrons, or two for the helium arrangement); main-group ions usually have one.
Bonding in which the attraction acts equally in all directions, as in ionic and metallic bonding, so each particle is not bonded to particular neighbours.
A molecule with no net dipole moment, because its bonds are non-polar or its bond dipoles cancel by symmetry, such as and .
The arrangement of six electron domains around a central atom, pointing to the corners of an octahedron with all neighbouring domains at 90°, as in and many complex ions.
The tendency of atoms to gain, lose or share electrons until they have eight electrons in their valence shell (two for hydrogen).
The loss of electrons by a species, or an increase in its oxidation state.
A small charge, or , on an atom in a polar bond, smaller than the charge of an electron.
The amide link, , that joins amino acid residues in peptides and proteins.
A covalent bond formed by the sideways overlap of two parallel p orbitals, with its electron density above and below the bond axis; a double bond contains one and a triple bond two.
A synthetic polymer material that can be moulded into shape, usually when heated.
A small molecule added to a polymer that fits between the chains, weakening the forces between them and making the material more flexible, as in flexible PVC.
A covalent bond in which the shared pair is attracted more strongly by one atom, because the atoms differ in electronegativity, giving partial charges and .
A molecule with a net dipole moment, because its bond dipoles do not cancel, such as and .
A solvent whose molecules have a permanent dipole, such as water; polar solvents can attract and surround ions, so many ionic compounds dissolve in them.
How easily the electron cloud of an atom or molecule is distorted; it increases with the number of electrons and size, and strengthens London forces.
A condensation polymer whose repeating units are joined by amide links, formed from a diamine and a dicarboxylic acid (or diacyl dichloride) or from amino acids; examples are nylon-6,6, Kevlar and proteins.
An ion made of two or more atoms joined by covalent bonds, such as ammonium, , or sulfate, .
A condensation polymer whose repeating units are joined by ester links, formed from a diol and a dicarboxylic acid or from a hydroxy acid; examples are PET and PLA.
A macromolecule made of many repeating subunits joined by covalent bonds, formed from small molecules called monomers.
The gain of electrons by a species, or a decrease in its oxidation state.
The smallest section of a polymer chain that repeats along its length; it is drawn in brackets with continuation bonds through the brackets and outside.
A number from 1 to 7 printed on a plastic item, usually inside a recycling symbol, that identifies the polymer it is made of so that plastics can be sorted for recycling.
The real structure of a species with resonance: a single structure that is an average of its resonance structures, with delocalized electrons and equivalent bonds of intermediate order.
One of two or more valid Lewis formulas for a species that differ only in the positions of electrons, not of atoms; they are joined by a double-headed arrow, ↔.
The molecular geometry of a species with four bonding pairs and one lone pair (five electron domains), the lone pair equatorial, as in .
A solid, such as silicon or germanium, whose electrical conductivity lies between that of a conductor and an insulator and increases as the temperature rises.
A covalent bond formed by the head-on overlap of two orbitals, with its electron density concentrated along the bond axis; every single bond is a sigma bond.
A covalent bond made of one shared pair of electrons.
The mixing of one s and one p orbital to give two sp hybrid orbitals at 180°, leaving two p orbitals for pi bonds; found in atoms with two electron domains.
The mixing of one s and two p orbitals to give three hybrid orbitals in a plane at 120°, leaving one p orbital for a pi bond; found in atoms with three electron domains.
The mixing of one s and three p orbitals to give four hybrid orbitals pointing to the corners of a tetrahedron, 109.5° apart; found in atoms with four electron domains.
The molecular geometry of a species with four bonding pairs and two lone pairs opposite each other (six electron domains), as in ; the bond angles are 90°.
The molecular geometry of a species with five bonding pairs and one lone pair (six electron domains), as in .
An alloy in which atoms of the added element, of similar size, take the places of some of the metal atoms in the lattice, as in brass.
A polymer made industrially, such as poly(ethene), PVC, nylon or PET.
The molecular geometry of a species with three bonding pairs and two equatorial lone pairs (five electron domains), as in , with bond angles just under 90°.
A short-lived dipole that forms when the electrons of an atom or molecule are momentarily spread unevenly.
The ability of a substance to transfer heat; metals conduct heat well because their delocalized electrons carry kinetic energy rapidly through the lattice.
A plastic that softens on heating and can be remoulded, because heating overcomes the intermolecular forces between its chains without breaking covalent bonds.
A polymer whose chains are joined by covalent cross-links, so it does not soften on heating but chars or decomposes instead.
An element whose atoms have an incomplete d-sublevel, or which forms at least one stable ion with an incomplete d-sublevel; most form ions with more than one charge.
The arrangement of five electron domains around a central atom: three equatorial at 120° in a plane and two axial at 90° to that plane, as in .
A covalent bond made of three shared pairs of electrons, as in ; the shortest and strongest bond between two given atoms.
The collective name for London (dispersion), dipole-induced dipole and dipole–dipole forces; it does not include hydrogen bonding.
The tendency of a substance to vaporize; substances with weak forces between their particles are volatile, while ionic compounds have low volatility.
The valence shell electron pair repulsion model: electron domains around a central atom repel each other and take up positions as far apart as possible, which predicts the shape of a molecule.