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General Properties of Transition Metals
Transition metal characteristics of elements Ti–Cu arise from an incomplete d sub-level in atoms or ions.
The characteristic properties include:
formation of coloured ions
variable oxidation state
A ligand is a molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons.
A complex is a central metal atom or ion surrounded by ligands.
Co-ordination number is the number of co-ordinate bonds to the central metal atom or ion.
Transition elements have an incomplete d-subshell that can form at least one stable ion with an incomplete d-subshell
Scandium and zinc do not fit the definition:
Elements of the 1st transition series are therefore titanium to copper
Typical metals but show the following additional properties:
• Variable oxidation states
• Complex ion formation
• Coloured compounds
Variable Oxidation States
Transition metals can form more than one positive ion – have variable oxidation states. Roman numerals denote the oxidation state on the metal ion.
Iron (Fe) can form Fe2+ (Fe(II)) and Fe3+ (Fe(III)) ions
This is a molecule or ion, with a central metal atom/ion, with a number of molecules/ions (ligands) surrounding it. A variety of ligands, of different number, can form bonds
chromium(III) can form [Cr(NH3)6]3+, [Cr(OH)6]3- and [Cr(H2O)6]3+ complex ions
For example, the colour of the [Cr(OH)6]3- complex (OS of Cr is +3) is dark green. The [Cr(NH3)6]3+ complex (3) is purple.
The transition element can change to various oxidation states by gaining electrons or donating electrons from reagents within the reaction
Substances can also be adsorbed onto their surface and are activated in the process
Electrons start to fill the lowest energy sub-shells first (Aufbau Principle)
The 4s overlaps with the 3d subshell (similar energy) so 4s fills first
For chromium and copper, an electron is promoted from the 4s to the 3d:
Cr: [Ar] 3d5, 4s1
Cu: [Ar] 3d10, 4s1
The half-full/full d configurations are energetically more stable
Cu(ll): [Ar] 3d9 so incomplete d sub-shell – compounds are blue
How to… Write the full electronic configuration of the manganese(lll) ion.
Write out the electron configuration of the atom first:
Mn atomic number = 25 therefore 25 protons & 25 electrons
1s2, 2s2, 2p6, 3s2, 3p6, 3d5, 4s2
Remove electrons - start from the 4s subshell
Mn(lll) = 3+ ion = 25 – 3 = 22 electrons: 1s2, 2s2, 2p6, 3s2, 3p6, 3d4
A ligand is a molecule/ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons to the bond (a Lewis base). It acts as a nucleophile
The number of dative (co-ordinate) bonds:
one dative bond – monodentate ligand
two dative bonds – bidentate ligand
more than 2 – multidentate ligand
Water, ammonia, chloride, cyanide (CN–), thiocyanate (SCN–)
1,2-diaminoethane (H2NCH2CH2NH2) or (‘en’), Ethanedioate ion (C2O42- )
Monodentate Ligand Examples
Bidentate Ligand Examples
Multidentate Ligand Examples
EDTA4- is a hexadentate ligand forming 6 dative covalent bonds
Complexes with water & ammonia
Water and ammonia molecules are neutral ligands - they have a lone pair of electrons able to form a dative covalent bond. Water and ammonia are small – 6 can fit around a central metal ion, each donating a lone pair of electrons, forming 6 dative bonds.
6 dative bonds = coordination number of 6
Overall charge is the sum of the charge on the central metal ion, and the charges on each of the ligands
cobalt(II) or chromium(II) complexes, with water or ammonia as ligands, will have an overall charge of 2+ (remember that water and ammonia are neutral molecules).
Complexes with hydroxide & chloride
Hydroxide and chloride ions are negatively charged ligands. Hydroxide ligands are small, so 6 of them can fit around a central metal ion and the complex formed will have a coordination number of 6
Chlorides are large so only 4 of them will fit around the metal ion. Complexes with 4 chloride ligands will have a coordination number of 4
A complex with chromium(III) as a central metal ion and hydroxide ions as ligands, will have an overall charge of 3-...
The central metal ion has a charge of 3+
Each hydroxide ligand has a charge of 1- = 6 (overall negative charge is 6-)
The overall positive charge is 3+
The overall charge on the complex is 3–
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