Download Introducing Transition Metals

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What is a transition metal?
The d block elements are found in the centre of the periodic
table. As you move across the d block, five d orbitals are
filled, up to a total of ten electrons.
Transition metals are d
block elements that can
form at least one stable
ion with an incomplete
d sub-level.
Transition metals have typical metal properties, such as
conducting heat and electricity, and high melting and boiling
points. They are sonorous, ductile, malleable and lustrous.
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Electron configurations
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Evidence of electronic structure
Successive ionization energies can be used to determine
the electronic structure of an element.
In a transition metal,
electrons are initially
removed from the 4s
sub-level and then the 3d
sub-level. There is only a
small energy difference
between these sub-levels.
When both sub-levels are
empty, the 4s sub-level is
slightly lower in energy and
is filled first.
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Successive ionization energies
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Transition metal electronic structures
When transition metals form ions, the 4s electrons are
removed before the 3d electrons. This means that nearly all
of them make stable 2+ ions.
Ti
1s22s22p63s23p63d24s2
Ti2+
1s22s22p63s23p63d24s0
Which Period 4 transition metals are likely to make
stable 1+ ions?
Chromium and copper because they lose the one electron
from their 4s sub-level.
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d-block elements or transition metals?
A d block element has its highest energy electron in its d
sub-level. A transition metal is a d block element which has a
partially filled d sub-level in at least one stable ion.
Scandium makes a stable
Sc3+ ion with an electronic
configuration of [Ar] 3d0 4s0
and is therefore not a
transition metal.
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Zinc makes a stable Zn2+
ion with an electronic
configuration of [Ar] 3d10 4s0
and is therefore not a
transition metal.
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d block elements vs transition metals
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Variable oxidation states
Transition metals can form a number of stable ions, each
with the metal in a different oxidation state.
Variable oxidation states are
possible because the 4s and 3d
sub-levels are very close in energy.
It is relatively easy to lose electrons
from either of these sub-levels.
The oxidation state of the metal in a
compound is noted as a Roman
numeral after the name of the metal.
Iron(II) means that the compound contains Fe2+, whereas
iron(III) contains Fe3+.
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Identify the oxidation states
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Oxidation states of vanadium
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Oxidation states and bonding
At lower oxidation states, transition metals form ionic bonds.
At higher oxidation states, transition metals cannot form
monatomic ions. Instead they bond covalently to form
compounds or molecular ions.
For example, manganese
forms ionic bonds in
manganese(II) chloride
and covalent bonds in the
MnO4– oxoanion.
Transition metals are often in their highest oxidation state
when bonded to very electronegative elements like oxygen
and fluorine.
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Common oxidation states
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Ligands
A ligand is any atom, ion or molecule which can donate a
pair of electrons to a metal ion. Ligands are Lewis bases
and nucleophiles.
Ligands are classified by the number
of dative covalent or coordinate
bonds that they can make.
Water molecules frequently act as
ligands. Each water molecule
makes a single bond with the
metal ion. Ligands which form
single coordinate bonds are called
unidentate or monodentate.
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The lone pair of
electrons on the oxygen
can be donated into the
partially filled d sub-level
of the transition metal.
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Bidentate ligands
Bidentate ligands contain two atoms that donate pairs of
electrons to form coordinate bonds. For example:
Ethane-1,2-diamine (en)
Both nitrogen atoms
donate lone pairs to the
metal ion.
Ethanedioate ion
The two single-bonded
oxygen atoms both
donate lone pairs to the
metal ion.
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Multidentate ligands
Multidentate ligands contain more than two atoms that
donate pairs of electrons to form coordinate bonds.
The EDTA4– ion forms
six coordinate bonds
with a metal ion.
Lone pairs are
donated by the four
negatively-charged
oxygen atoms and the
two nitrogen atoms.
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Bonding atoms in ligands
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Identifying ligands
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Coordination number
The coordination number is the number of coordinate
bonds to the metal ion. This is different to the oxidation state
of the metal ion or complex.
Hexaaquacopper(II)
Coordination number = 6
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Tetrachlorocobalt(II)
Coordination number = 4
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What is a complex?
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Identify the complex ion
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Shapes of complex ions
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Cis–trans isomerism
Stereoisomerism is where molecules have the same
molecular formula, but a different arrangement of atoms in
space.
Cis–trans isomerism
occurs because the
ligands cannot rotate
around the central
metal ion.
cisplatin
transplatin
Different stereoisomers can have different chemical properties.
Cisplatin is an isomer that is used as an anticancer drug. The
trans isomer, transplatin, has no known medical use.
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Optical isomerism
Another form of stereoisomerism is optical isomerism, in
which a molecule can exist as two forms that are nonsuperimposable mirror images of each other, just like a left
hand and right hand.
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Transition metal complexes
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Identify the complex shape
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Glossary
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What’s the keyword?
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Multiple-choice quiz
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