Key Terms

actinide series

(also, actinoid series) actinium and the elements in the second row or the f-block, atomic numbers 89–103

bidentate ligand

ligand that coordinates to one central metal through coordinate bonds from two different atoms

central metal

ion or atom to which one or more ligands is attached through coordinate covalent bonds

chelate

complex formed from a polydentate ligand attached to a central metal

chelating ligand

ligand that attaches to a central metal ion by bonds from two or more donor atoms

cis configuration

configuration of a geometrical isomer in which two similar groups are on the same side of an imaginary reference line on the molecule

coordination compound

stable compound in which the central metal atom or ion acts as a Lewis acid and accepts one or more pairs of electrons

coordination compound

substance consisting of atoms, molecules, or ions attached to a central atom through Lewis acid-base interactions

coordination number

number of coordinate covalent bonds to the central metal atom in a complex or the number of closest contacts to an atom in a crystalline form

coordination sphere

central metal atom or ion plus the attached ligands of a complex

crystal field splitting (Δ_oct)

difference in energy between the t_2g and e_g sets or t and e sets of orbitals

crystal field theory

model that explains the energies of the orbitals in transition metals in terms of electrostatic interactions with the ligands but does not include metal ligand bonding

d-block element

one of the elements in groups 3–11 with valence electrons in d orbitals

donor atom

atom in a ligand with a lone pair of electrons that forms a coordinate covalent bond to a central metal

e_g orbitals

set of two d orbitals that are oriented on the Cartesian axes for coordination complexes; in octahedral complexes, they are higher in energy than the t_2g orbitals

f-block element

(also, inner transition element) one of the elements with atomic numbers 58–71 or 90–103 that have valence electrons in f orbitals; they are frequently shown offset below the periodic table

first transition series

transition elements in the fourth period of the periodic table (first row of the d-block), atomic numbers 21–29

fourth transition series

transition elements in the seventh period of the periodic table (fourth row of the d-block), atomic numbers 89 and 104–111

geometric isomers

isomers that differ in the way in which atoms are oriented in space relative to each other, leading to different physical and chemical properties

high-spin complex

complex in which the electrons maximize the total electron spin by singly populating all of the orbitals before pairing two electrons into the lower-energy orbitals

hydrometallurgy

process in which a metal is separated from a mixture by first converting it into soluble ions, extracting the ions, and then reducing the ions to precipitate the pure metal

ionization isomer

(or coordination isomer) isomer in which an anionic ligand is replaced by the counter ion in the inner coordination sphere

lanthanide series

(also, lanthanoid series) lanthanum and the elements in the first row or the f-block, atomic numbers 57–71

ligand

ion or neutral molecule attached to the central metal ion in a coordination compound

linkage isomer

coordination compound that possesses a ligand that can bind to the transition metal in two different ways (CN⁻ vs. NC⁻)

low-spin complex

complex in which the electrons minimize the total electron spin by pairing in the lower-energy orbitals before populating the higher-energy orbitals

monodentate

ligand that attaches to a central metal through just one coordinate covalent bond

optical isomer

(also, enantiomer) molecule that is a nonsuperimposable mirror image with identical chemical and physical properties, except when it reacts with other optical isomers

pairing energy (P)

energy required to place two electrons with opposite spins into a single orbital

platinum metals

group of six transition metals consisting of ruthenium, osmium, rhodium, iridium, palladium, and platinum that tend to occur in the same minerals and demonstrate similar chemical properties

polydentate ligand

ligand that is attached to a central metal ion by bonds from two or more donor atoms, named with prefixes specifying how many donors are present (e.g., hexadentate = six coordinate bonds formed)

rare earth element

collection of 17 elements including the lanthanides, scandium, and yttrium that often occur together and have similar chemical properties, making separation difficult

second transition series

transition elements in the fifth period of the periodic table (second row of the d-block), atomic numbers 39–47

smelting

process of extracting a pure metal from a molten ore

spectrochemical series

ranking of ligands according to the magnitude of the crystal field splitting they induce

steel

material made from iron by removing impurities in the iron and adding substances that produce alloys with properties suitable for specific uses

strong-field ligand

ligand that causes larger crystal field splittings

superconductor

material that conducts electricity with no resistance

t_2g orbitals

set of three d orbitals aligned between the Cartesian axes for coordination complexes; in octahedral complexes, they are lowered in energy compared to the e_g orbitals according to CFT

third transition series

transition elements in the sixth period of the periodic table (third row of the d-block), atomic numbers 57 and 72–79

trans configuration

configuration of a geometrical isomer in which two similar groups are on opposite sides of an imaginary reference line on the molecule

weak-field ligand

ligand that causes small crystal field splittings