Transcript Topic 13.2 Periodicity First Row d

Topic 13.1 First Row d-Block Elements
Assessment Statements
 13.2.1 List the Characteristic properties of transition elements
 13.2.2 Explain why Sc and Zn are not considered transition
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elements
13.2.3 Explain the existence of variable oxidation number in ions
of transition elements.
13.2.4 Define the term ligand.
13.2.5 Describe and explain the formation of complexes of dblock elements.
13.2.6 Explain why some complexes of d-block elements are
coloured.
13.2.7 State examples of the catalytic action of transition
elements and their compounds.
13.2.8 Outline the economic significance of catalysts in the
contact and Haber Process
Assessment Statements
 13.2.1 List the Characteristic properties of
transition elements
Where are the transition metals?
The transition metals are the block of elements
located between group 2 and group 3 of the periodic
table.
group 2
group 3
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
La Hf Ta W Re Os Ir Pt Au Hg
Ac Rf Db Sg Bh Hs Mt Ds Rg ?
Here, the word
‘transition’ is
used to mean
‘in-between’.
What are the transition metals?
Why are they called the ‘typical metals’?
There are over 30 transition
metals.
They include most of the
metals we are familiar
with and use everyday,
such as iron, copper and
gold.
However, there are many
transition metals that are
less familiar to us,
because they are very
rare or have few uses.
The transition metals are known as ‘typical’ metals.
Why do you think this might be?
What are the properties of the transition metals?
The transition metals are known as ‘typical’ metals
because of their physical properties. They are:
 lustrous (bright and shiny).
 hard and strong.
 high density.
 malleable (can be bent and pressed into different
shapes) and ductile (can be drawn into wires).
 good conductors of heat and electricity.
 high melting and boiling points (except mercury,
which is liquid at room temperature).
How do the transition metals compare with the alkali
metals?
Comparing properties of different metals
How do the properties of transition metals compare
with those of alkali metals?
Compared to the alkali metals, the transition
metals:
 are harder and stronger. They cannot be cut with a
knife.
 are more dense. This means that in a fixed volume
of metal there are more atoms of a transition
metal than there are of an alkali metal.
 have higher melting and boiling points – except
mercury.
13.2 First row D-Block elements
3d spans from Scandium to Zinc
Transition
elements are a
subset of the
d-block that
have a partially
filled d-sublevel
in one of its
common
oxidation
states.
Physical properties: 1 High electrical and thermal conductivity
2 High melting point
3 Malleable (easy beaten in shape)
4 High tensile strength (can hold large loads without
breaking
5 Ductile (can be drawn easily into wires)
Comparing densities of metals
Comparing melting points of metals
True or false?
Other Properties (required for IB)
 Form coloured ions
 Form complexes
 Have variable oxidation states
 Show catalytic activity
These will be explained in the following assessment
statements
Assessment Statements
 13.2.2 Explain why Sc and Zn are not considered
transition elements
 13.2.3 Explain the existence of variable oxidation
number in ions of transition elements.
==== Sc always forms 3+ ions, it
loses all its valence
electrons, 4s2 and 3d1.
Cr and Cu have unusual
electron configuration due
the stability of half filled
and filled 3d sublevel
==== Zn always forms 2+ ions,
it loses the 4s2 electrons
and keeps the 3d full.
The metals in 3d can lose different amounts of electrons to form different ions.
These ions are all said to be in different oxidation states.
The oxidation state (oxidation number) is the same as the charge on the ion,
ex. Cr3+ has an oxidation state of +3; Cr2+ has an oxidation state of +2.
Sc and Zn don’t share all the properties of transition elements
as they don’t have a partially filled d block. (they cannot form
multiple ions)
Oxidation state first row transition series (Memorize the red ones)
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
+1
+3
+2
+2
+2
+2
+2
+2
+2
+2
+3
+3
+3
+3
+3
+3
+3
+3
+4
+4
+4
+4
+4
+4
+4
+5
+5
+5
+5
+5
+6
+6
+6
+2
+7
Important notes!
All metals show +2 and +3 the M3+are more stable from scandium to chromium,
M2+ is more stable for the latter
Oxidation states above +3 show more covalent character
Compounds with higher oxidation state tend to be oxidizing agents (K2Cr2O7)
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
Ti2+
1s22s22p63s23p63d24s2
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.
Explanation of Variable Oxidation
Number Transition Elements
s-block metals lose s electrons easily but the ionization energies for the
inner electrons are so high that these are never lost.
For this reason they always have the same oxidation state - a +1 ion has oxidation
number +1. (Mg, Ca , Al etc…)
Ionization energy increases abruptly when all outer S electrons are
removed.
Element
1st IE 2nd IE
3rd IE
4th IE
5th IE
6th IE
Ti
685
1310
2652
3564
11345
15643
V
759
1560
2955
4300
5400
12645
Ionization energies Titanium and Vanadium
Ionization energy increases for Titanium and Vanadium is more gradual
as the 3d and 4s orbitals are close in energy level
Titanium shows oxidation state +2, +3, +4, (after that there is a large jump) no 5+
Vanadium shows oxidation state +2, +3, +4, +5 (after that there is a large jump) no
6+
Write the oxidation number in
the brackets
CrCl3
Cr2O72−
• MnO2
• MnO4−
• Fe2O3
• Cu2O
chromium ( ) chloride
dichromate ( ) ion
manganese ( ) oxide
permanganate ( ) ion
iron ( ) oxide
copper ( ) oxide
Its time to wake up!!!!!
Work out the oxidation state of the metal in
each ion below.
Vanadium
VO4 3-, [VO(H2O)5]2+, [V(H2O)6]3+
Chromium
CrO42- , [Cr(H2O)6]3+
Iron
[Fe(H2O)6]3+
Transition Metal Compounds
As most transition metals can form different ions, this means
For example:
they can form multiple compounds.
Copper can form Cu+, which
can make the red compound
copper (I) oxide – Cu2O.
Copper can also form
Cu2+, which can make
the black compound
copper (II) oxide – CuO.
The number in brackets indicates how many electrons have
been lost.
Transition Metal Compounds and Colour
Most transition metals form coloured compounds.
For example:
 Iron (II) oxide (FeO2) is
black.
 Iron (III) oxide (Fe2O3) is
red/brown – when hydrated
this is rust.
 Copper (II) sulfate crystals
(CuSO4.H2O) is blue – these
can be turned white by heating
the crystals to remove the
water.
Uses of Coloured TM Compounds
The colour of many gemstones
comes from the presence of
transition metal compounds.
For example, the gemstone jade
contains iron.
The coloured compounds of
transition metals can also be used in
many ways, for example:
 to colour stained glass windows
 to colour paints
 as coloured glazes on
pottery.
How are transition metal ions identified?
The presence of transition metal ions in a solution can
be tested by adding sodium hydroxide solution.
If transition metal ions are present, a metal hydroxide
is formed. This is insoluble and so appears as a solid
called a precipitate.
Different metal ions produce different coloured
precipitates:
 Fe2+ ions produce a grey/green
precipitate of Fe(OH)2 .
 Fe3+ ions produce an orange/
brown precipitate of
Fe(OH)3 .
 Cu2+ ions produce a blue
precipitate of Cu(OH)2 .
Assessment Statements
 13.2.4 Define the term ligand.
 13.2.5 Describe and explain the formation of
complexes of d-block elements.
Coordinated Ligands
 Ligands are the molecules (or ions) which donate
an electron pair to form a dative covalent bond
with the central transition metal atom (forming a
complex molecule or ion).
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
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.
The lone pair of electrons
on the oxygen can be
donated into the partially
filled d sub-level of the
transition metal.
Bidentate ligands contain two atoms that donate pairs of
electrons to form coordinate bonds. For example:
Bidentate Ligands
Ethane-1,2-diamine
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.
Multidentate ligands contain more than two atoms that
donate pairs of electrons to form coordinate bonds.
Multidentate ligands
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.
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.
Coordination number
Hexaaquacopper(II)
Coordination number = 6
Tetrachlorocobalt(II)
Coordination number = 4
Complexes
Ligands
The ions of d-block metals and those in the lower section of
the p-block (like lead) have unfilled valence d and p orbitals.
These orbitals can accept a lone pair of electrons from species, known as
ligands, to form a dative covalent bond between the ligand and the metal
ion.
Ex. An NH3/H2O (ligands) molecule can donate its non-bonding electron
pair to a Cu2+ ion.
The number of dative or coordinate rents bonds from the ligands to
the central ion is the coordination number: C.
Coordination Number
CN - Number of ligand atoms bonded directly to the central metal ion.
Specific for given metal ion in particular Oxidation #.
 i.e., [Co(NH3)6]+ CN = 6 Ligand # = 6
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[Ag(NH3)2]+
CN = 2
Ligand # = 2

[Co(en)3]+ CN = 6 Ligand # = 3
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Geometry of Complex is related to CN.
 CN = 2
Linear
CN= 4
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CN = 5
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Tetrahedral (d10)
Sq Planar (d8)
Trigonal bipyramidal
Square Pyramide
CN = 6
Octahedral
F
F
Br
F
F
I
I
I
F
P
F
F
I
I
F
F
F
Br
F
S
F
F
F
F
Coordinated Complexes and Coordination
Number
Coord
Number
Shape
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2
Linear
[CuCl2]-, [Ag(NH3)2]+, [AuCl2]-
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4
Square Planar
[Ni(CN)4] 2-, [PdCl4]2[Pt(NH3)4] 2+, [Cu(NH3)4] 2+
Example
F
F
Br
F
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4
Tetrahedral
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6
Octahedral
F
[Cu(CN)4] 3-, [Zn(NH3)4]2+
[CdCl4] 2-, [MnCl4] 2-
[Cu(H2O)6] 3+, [V(CN)6] 4-,
[Cu(NH3)4Cl2] +, [Co(en)3] 3+

F
F
F
S
F
F
F
Examples of some complex ions:
Complex
Ligand
Coordinatio
n number
Oxidation
number
central ion
shape
[Fe(H2O)6]3+
H2O
6
3+
Octahedral
[Co(NH3)6]3+
NH3
6
3+
Octahedral
[CuCl4]-
Cl-
4
2+
Tetrahedral
[Ag(NH3)2]+
NH3
2
1+
Linear
MnO4-
O2-
4
2+
Tetrahedral
PtCl2(NH3)2
Cl- and NH3
4
2+
Tetrahedral
[Al(H20)]3+
H2O
6
3+
Octahedral
The color of transition metal ion complexes
If white light passes through the complex ion colored light is
absorbed, electrons are excited to the higher d orbitals and the
opposite color is seen.
For example [Fe(H2O)6]3+ appears yellow because it’s ions absorb blue
Assessment Statements
 13.2.6 Explain why some complexes of d-block
elements are coloured.
Colour of ions
When a colour change occurs in the reaction of a
transition metal ion, there is a change in at least
one of the following: Oxidation state
 Co-ordination number
 Ligand
How do we see colour?
Most transition metal compounds appear coloured. This is because
they absorb energy corresponding to certain parts of the visible
electromagnetic spectrum. The colour that is seen is made up of the
parts of the visible spectrum that aren’t absorbed.
For example, a red
compound will absorb all
frequencies of the
spectrum apart from red
light, which is
transmitted.
What happens when light is absorbed?
In transition metal ions, the d sub-level is only partially filled. This
means that electrons can move between d orbitals.
In a transition metal
complex, the relative
energies of the d orbitals
change. Electrons can be
promoted to higher energy
orbitals.
For electrons to be promoted, they need to absorb light
energy of a particular frequency. This frequency
depends on the precise difference in energy between
the d orbitals.
Colors of transitional ions
Sc 3+ Colorless
Ti 3+ Violet
V3+ Green
Cr 3+ Violet
Mn2+ Pink
Fe3+ Yellow
Co2+ pink
Ni2+ Green
Cui2+ Blue
Zn2+ Colorless
Note regarding Complex ions:
The formation of complex ions stabilizes certain oxidation states.
The formation of a complex ion can also affect the color of a metal
ion in solution.
For many complexes, ligand replacement can occur depending on
which complex is more stable.
Transition metals absorb light as the d orbital splits into two
sublevels
In an isolated atom all of the d sublevel electrons have the same
energy.
When ligands are attached to transition metal ions, the d orbitals may
split into two groups. Some of the orbitals are at a lower energy than
the others
The difference in energy of these orbitals varies slightly with the
nature of the ligand or ion surrounding the metal ion
When white light passes ,light of a particular frequency is
absorbed. The result is a colored compound it shows the
complimentary color.
Various oxidation
states of Nickel (II)
The colour of a transition metal compound is determined
by the difference in energy between its d orbitals.
Factors affecting colours
This can be affected by several factors:

size and type of ligands

coordination number

strength of metal–ligand bonds

oxidation state.

complex shape
[Cr(H2O)6]3+
[Ni(H2O)6]2+
[Fe(H2O)6]2+
[Fe(H2O)6]3+
Colours of complexes
A transition metal will appear different colours
in complexes with different ligands.
For example:
[Cu(H2O)6]2+
[CuCl4]2–
Transition Metals (ions) as Catalysts
The colors of the ions and complex ions of d block
elements depends on:
1 Nuclear charge hence identity central atom
2 Charge density of the ligand eg: NH3 has a higher charge density as
H2O
3
Number of D electrons, hence charge
4 Shape of the complex
Assessment Statements
 13.2.7 State examples of the catalytic action of
transition elements and their compounds.
 13.2.8 Outline the economic significance of
catalysts in the contact and Haber Process
Catalysts
 A catalyst enables a reaction to happen by
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providing an alternative pathway with a lower
activation energy.
Many D block elements are catalysts for various
chemical reactions.
The transition metals form complex ions with
ligands that can donate lone pairs of electrons.
This results in close contact between the metal
ion and the ligand.
Heterogeneous (different state) catalysts are
more common than homogeneous.
A catalyst is a substance that speeds up reactions by providing an
alternative reaction route with lower activation energy.
Transition metals as catalysts
Transition metals are good catalysts for two
reasons:
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they show variable oxidation states. This allows
them to act as intermediates in the exchange of
electrons between reacting species.

they provide a surface for reactions to occur. The
metal forms weak bonds to the reacting species,
holding them in place.
Heterogeneous Catalyst
 Refers to the form of catalysis where the phase of
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the catalyst differs from that of the reactants.
Phase here refers not only to solid, liquid, vs gas, but
also immiscible liquids, e.g. oil and water.
The great majority of practical heterogeneous
catalysts are solids and the great majority of
reactants are gases or liquids.
Heterogeneous catalysis is of paramount importance in
many areas of the chemical and energy industries.
Heterogeneous catalysis has attracted Nobel prizes
for Fritz Haber and Carl Bosch in 1918, Irving
Langmuir in 1932, and Gerhard Ertl in 2007.
There are two types of catalysts: homogeneous and
heterogeneous.
Types of catalysts
Homogeneous catalysts are in the
same phase as the reaction species,
e.g. two miscible liquids.
Heterogeneous catalysts are in a
different phase to the reaction
species, e.g. two immiscible liquids.
Homogeneous Catalysis
 A sequence of reactions that involve a catalyst in
the same phase as the reactants.
 Most commonly, a homogeneous catalyst is
codissolved in a solvent with the reactants.
 Enzymes are homogeneous catalysts that are
essential for life but are also harnessed for
industrial processes. A well studied example
carbonic anhydrase, which catalyzes the release
of CO2 into the lungs from the blood stream
Catalysts are often very expensive. Maximising the efficiency of
catalysts minimizes the cost. One method of increasing efficiency is
to increase the surface area of the catalyst.
Improving Catalyst Efficiency
In a catalytic converter, a
ceramic honeycomb
structure is coated with
finely divided rhodium and
platinum. The ceramic
support medium is inert
but it increases the
surface area of the
catalyst and reduces the
amount needed.
Some Common D Block Catalysts (heterogeneous)
 Examples of D block elements that are used as catalysts
In a catalytic converter
Decomposition of hydrogen peroxide
Haber process: N2 + 3H2 <=> 2NH3
Removal 2CO + 2NO = 2CO2 + N2
:
Most cars in the UK are fitted with catalytic converters. These convert pollutants
such as carbon monoxide, nitrogen oxides and unburnt hydrocarbons into carbon
dioxide, nitrogen and water; gases which are found naturally in our atmosphere.
Catalytic converters
Catalytic converters contain an inert
honeycomb structure coated with the catalyst
– platinum and rhodium. The exhaust gases
enter through the holes and react on the
catalyst surface.
Catalytic converters are easily poisoned, especially by anti-knock additives. They do
not work when cold and reduce fuel economy by 2-10%.
Many industrial processes use heterogeneous catalysts. Catalysts increase
the rate of a chemical reaction, although the equilibrium position is
unchanged.
The Haber Process
The Haber Process produces ammonia from hydrogen and
nitrogen gases. It uses a heterogeneous iron catalyst.
iron catalyst
N2(g) + 3H2(g)
2NH3(g)
Over several years, the iron catalyst becomes poisoned by
impurities such as sulfur compounds. When the efficiency
of the catalyst is greatly reduced, it must be replaced.
Sulfuric acid is produced by the Contact Process using a
heterogeneous catalyst of vanadium(V) oxide.
The Contact Process
2SO2 + O2
2SO3
There are two steps in the reaction.
SO2 + V2O5
2V2O4 + O2
SO3 + V2O4
2V2O5
The oxidation number of vanadium changes from +5 to +4 to +5 again
over the course of the reaction.
Methanol is produced by two consecutive reactions.
Producing Methanol
Synthesis gas, a mixture of carbon monoxide and hydrogen, is first
produced from the reaction of methane and steam.
Step 1
CH4(g) + H2O(g)
CO(g) + 3H2(g)
This gas is then used to produce methanol. The reaction is
sometimes catalysed by chromium(III) oxide, (Cr2O3).
Step 2
CO(g) + 2H2(g)
synthesis gas
CH3OH(g)
methanol
Ions of transition metals a s homogeneous
Catalysts
Fe2+ in heme , oxygen is transported and forms a weak
bond with the heme group (central ion in heme) is Fe2+
Co3+ in vitamin B12, part of the vitamin B12 consist of
octahedral CO3+
Vitamin B12 is used for the production of blood
Spot the uses of the transition metals
How many everyday uses of transition metals can you see?
What are the uses of the transition metals?
activity
The lenses of polychromic sunglasses contain silver halide nanoparticles.
These particles are transparent in artificial light. A photochemical reaction
occurs on exposure to UV radiation, found in sunlight.
Polychromic Sunglasses
UV radiation changes the shape of the
nanoparticles. They absorb some of the
visible light, so the lenses appear darker.
Without UV radiation, the molecules
return to their original shape and the
lenses appear colourless again.
Glass blocks the UV light responsible for this reaction, so
polychromic lenses will not darken in a car or when looking out of a
window.
Platin is a platinum complex that forms cis–trans stereoisomers. The cis
isomer, cisplatin, is used as an anti-cancer drug. The trans isomer, transplatin,
doesn't have the same effect and is not used in chemotherapy.
Chemotherapy Drugs
cisplatin
transplatin
Cisplatin is administered intravenously. It is very useful in
treating solid tumours.
How Does Cisplatin Act?
For a cell to replicate, the double helix DNA molecule must unwind.
Cisplatin prevents it from unwinding by forming coordinate bonds
with the DNA bases. Nitrogen atoms in the bases displace the
ammonia ligands in the cisplatin complex.
Cisplatin is an important drug used to prolong the life of cancer
patients. However, there are some risks associated with its usage.
Risks of Cisplatin

Cisplatin also prevents normal
cells in the body from
replicating.

Patients may experience sideeffects, ranging from nausea and
vomiting to life-threatening
complications such as kidney
damage.

Patients can become resistant to cisplatin.
Most transition metal compounds are coloured and many are used in
paints and dyes.
Paints and Dyes
Copper compounds produce very
vibrant blue colours. Phthalocyanine
blue is a copper complex used in paint
dyes. It is very stable and insoluble in
water.
Titanium dioxide is a white solid at
room temperature. Nanoparticles
of titanium oxide are used to
whiten paper and as a white
pigment in paint.
An alloy is a solid mixture of two or more metals, that can also
contain other non-metal elements. Alloys often have properties
that are very different to their constituent metals.
Alloys
Carbon is added to iron to make an
alloy of steel, which is much stronger
than iron.
Chromium can also be added to make
stainless steel, which is resistant to
corrosion.
Copper is used in many different alloys, such as
brass, bronze and coinage metals. The copper
content of an alloy can be estimated by titration
with I2/S2O32–.