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Introduction
The three series of elements situated in the periodic table following the alkaline earth
metals are described as transition metal; this term is sometime extended to include the
lanthanide and actinide elements.
There position in the periodic table is between the s-block and p-block elements, their
properties are transitional between the highly reactive metallic elements in the s-block,
which typically form ionic compounds, and the elements of the p-block, which are
largely covalent. In the s- and p-block electrons are added to the outer shell of the atom,
in the d-block electrons are added to the penultimate shell explaining from 8 to 18
electrons. The transitional elements typically have an incompletely filled d level
however, in group 12 (the zinc group) has a d10 configuration, an complete d shell,
compounds of these elements are not typical and show some difference from the other in
the series.
They exhibit a number of characteristic properties, which distinguish them from other
groups of elements:
1)
They are all metals and as such are lustrous and deformable and have high
electrical and thermal conductivities, in addition their melting and boiling points tends to
be high and they are generally hard and strong and from alloys with other metals.
2)
Most of them display numerous oxidation states, which vary by step of 1 rather
than 2 as is usually the case with those main-group elements, which exhibit more than
one oxidation state
The oxidation state shown by the transition elements maybe related to t`eir electronic
structure, i.e. Calcium-block element preceding the first row transition elements has the
electronic structure:
Ca 1s 2 2s 2 2p 6 3s 2 3 p6 4s 2
It might expected that the next ten transitional elements would follow this trend of
electronic configuration, this is true, except for Cr and Cu this is because one of the selectron move in to the d-shell, this result in additional stability where the d-orbital are
exactly half filled or completely filled
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Electronic structure
d 1s 2
d 2s 2
d3s2
d 5 s1
d5s2
d6s2
d7s2
d8s2
d 10 s 1
d 10 s 2
Oxidation
State
I
I
II
II
II
II
II
II
II
II
II
II
III
III
III
III
III
III
III
III
III
IV
IV
IV
IV
IV
IV
IV
V
V
V
V
V
VI
VI
VI
VII
Sc could have an oxidation number of (+2) if both s-electrons are used for bonding and
(+III) when both s-electrons and one d-electrons are involved. The rest of the transition
series follows an similar trend, by varying the number of d-electrons used in bonding,
varying oxidation states would result (see table)
3)
They have an unparallel propensity for forming co-ordination compounds with
Lewis base, coordination compounds (or complex) is formed when a Lewis base (ligand)
is attached to a Lewis acid (acceptor) by means of a lone-pair of electrons. Where the
ligand is composed of a number of atoms, the one directly attached to the acceptor is
called the ''donor atom'' this type of bonding is exemplified by the addition compounds
formed by the trihalides of the elements of the group 13, it is also the basis of much of the
chemistry of the transition elements.
this ability to from complexes is in contrast to the s- and p-block elements, which only
form a few complexes due the transition elements have small, highly charge and have
vacant low energy orbitals to accept ions lone pairs of electrons donated by other groups
or ligands.
General chemistry of scandium (Group 3 element)
Scandium: {Ar} 3d1 4s2
Properties of the element: soft slivery-white metals and display properties which might be
expected for the element following the strongly electropositive alkaline-earth metal and
before the transition metal proper, scandium is less electropositive than its successors in
group 2 but are electropositive than it successors in the transition series.
The elements always exist in oxidation state (+ III) and occurs as M3+
Scandium is classed, as a class-a acceptors (''hard acid'') and for, this require the removal
of the two s and one d electron, as a result the ions have a d 0 configuration and d-d
spectra are impossible, their compounds are colourless and diamagnetic. The properties
of scandium are similar in some ways to aluminium, the sum of the first three-ionisation
energies for Sc is a little less than the sum of for Al.
The metals have moderately high standard electrode potentials and are quite reactive,
tarnish in air and burn in dioxygen giving oxides M2O3.
2Sc + 3O2
2Sc2 O3
The metal react slowly with cold water but more rapidly in hot water liberating H2 ,
forming either the basic oxide or the hydroxide
Sc(OH)3 appears not to exist as a definite compound, but the basic oxide ScO.OH is
amphoteric like Al(OH)3 and dissolves in NaOH liberating H2.
Sc +3NaOH +3H2O
Na3 [Sc(OH)6] + 11/2 H2,
The oxides and hydroxides form salt with acid.
The metal react with halogens forming trihalides MX 3 resembling halides of Ca, the
fluoride are insoluble (CaF2) and other halides are diquescent and very soluble (like
CaCl2)
Anhydrous ScCl3 differs from AlCl3, as ScCl3 is monomeric whilst (AlCl2) 2 are
dimeric, also ScCl3 show no friedel ©Crafts catalytic properties. The salt generally
resemble that of Ca and fluorides, carbonates, phosphates and oxalates are insoluble.
The metal react with hydrogen on heating to x< 300oC, forming highly conducting
compounds (MH2), containing not M2+, but probably contain M 3+ and 2H © with an
extra electron in a conduction band this is true for the rest of the metal in the group
except for Sc since they absorb more H2 and loose their conducting power as a result
their compounds are not quite stoichiometric having the composition similar to MH3
(exact composition depends upon temperature and pressure of the hydrogen), the
hydrides react with water liberating H2and are salt like(ionic) hydrides containing the
hydride
Ion H-.
Sc forms carbide (ScC2) when the oxide is heated with carbon to x<1000 oC, the carbide
React with water liberating ethyne
Sc2O3 + C
2ScC2
C2H2 + ScO.OH
The carbide contains Sc3+ ions and C2-2 ions and the free electrons are delocalises into a
conduction band giving some metallic conduction.
Despite the charge of +3, the metal ions do not have a strong tendency to form complexes
due to the large size but Sc3+ form complexes more readily that the rest of the metal
within the group [Sc (OH) 6] 3And [ScF6] 3- both having the coordination number of 6 and is octahedral in shape
The most common donor atom in complexes is O, particularly with cheating ligands;
therefore the complexes are form with strong complexing agents such as oxalic acid,
citric acid, acetylacetone and EDTA.
[Sc (acetylacetone) 3] has a coordination of 6 and is octahedral.
NO3- and SO42- also act as bidentate ligand and form complexes with high
coordination numbers, in [Sc (NO3) 5] 2- four of the NO3- are bidentate and the
remaining NO3- unidentate giving an coordination number of 9.
General chemistry of zinc (Group 12 element)
Zinc: {Ar} 3d10 4s2
Zn show few of the properties associated with a typical transitional elements, this is due
to they having a complete d shell, which is not available for bonding
Zn does not show variable valency.
Zn has a d 10 electronic configuration and therefore cannot produce d-d spectra, as a
result, many of their compounds are white, the group as a whole are smaller (size of the
metal atom) therefore posses greater polarizing power than the group 2 metal, increasing
the chance of covalency and the charge transfer.
The melting and boiling point are very low, explaining why the metal is more reactive
than copper group, (the ionisation energies for the two group suggest the reverse)
The metal are relatively soft compare with the other transition elements, this maybe due
to d-electrons do not participate in metallic bonding, Zn are an slivery solid which tarnish
rapidly in moist air, its also dissolve in dilute non-oxidizing acids, liberating H2 and react
with oxidizing acids (HNO3, H2SO4) forming salts and evolving a mixture of oxides of
N2 and So2. Zn is also show amphoteric prosperities, soluble in alkalis forming zincates
Na2 [Zn (OH) 4], Na [Zn (OH) 3.H2O] similar to those of aluminates.
Complexes:
Zn2+ form complexes with O donor ligands and also with N and S donor ligands, but are
reluctant to bond to O, Zn
Do form complexes with CN © e.g. [Zn (CN) 4] 2-; since the element has an, d 10
configuration there is no crystal field
Stabilization energy.
Two and three coordinate complexes are rare for Zn.
Zn2+ occur largely in four co-ordination as tetrahedral complexes such as [MCl4] 2-, [M
(H2O)] 2+ and etc where M=Zn.
Five coordinate are not common example are [Zn (terpyridyl) Cl2] which has a trigonal
bipyramid shape
Zn also form several six coordinate octahedral complexes such as [M (H2O) 6] 2+, [M
(NH3) 6] 2+
And etc where M=Zn, however the octahedral complexes are not very stable due to the
small size of the atom.
There are few example of complexes with coordination of 7, [Zn (No3) 4] 2-, involving
bidentate O donor ligands such as NO3 © in which two O atoms occupy co-ordination
position. Zinc forms basic zinc acetate (CH3COO) 6.Zn4O very much like basic
beryllium acetate both in structure and properties, however the Zinc complexes is more
readily hydrolyses as Zinc can increase its coordination number to 6
Conclusion
Even though Sc and Zn are place in the first row transition element series, they are not
truly transitional element; they do some limited proprieties similar to that of transitional
elements such as high melting and boiling point, Sc has melting point of 2748k, Zinc
behave atypically due it having an complete d-shell, therefore the d electrons does not
participate in metallic bonding this explain why zinc only has an melting point of 907k.
Many transitional elements has melting point X<2500K.
They both lack the ability to form wide range of structural complexes show by
the rest of the transitional elements (due to their limited oxidation state which can be
relate to by their electronic configuration. See table in introduction) all the transitional
elements have variable oxidation states, Sc does show 2 variable oxidation state, Zn only
has one since it has a complete d-shell.
All the element in first row transitional series, have an unparallel propensity for forming
co-ordination compounds with Lewis base, coordination compounds (or complex) is
formed when a Lewis base (ligand) is attached to a Lewis acid (acceptor) by means of a
lone-pair of electrons, Sc and Zn do show evidence of this but only to an limited extent,
Sc does not have an strong tendency to form complex despite it charge 3+, this is due the
size of the Sc atom and it electronic configuration: [3d1 4s2] the chemistry of the element
is almost restricted to that of the trivalent ion.
Zn does show some tendency to from complexes, coordination from 2&x&8 are know.
(Since the element have a d10 configuration there is no crystal fields splitting energy.
Both elements do show some properties of transitional elements but they cannot be class
as transitional elements.
The classification that they are not transitional metal is correct.
Additional note:
(The colourless compound of SC and Zn can be explain, since Sc and Zn having an
electronic configurations of d 0 and d10 respectively, therefore obtaining an d-d spectra
for both is not possible and there complex are largely colourless)
However colour may arise from an entirely different cause in ions with incomplete d
shells, in a free isolated gaseous ion, the five d orbitals are degenerate (all five are the
same in term of energy), in solution the ions is surrounded by solvent molecule if it in
solution and by other ligands if it in a complex or by other ions in a crystal lattice.
The surrounding group affect the energy of some d orbital more so than other, therefore
the d orbitals are no longer degenerate and they form two groups of orbitals with an
different in energy, in transitional element ions with a partly filled shell it is possible to
promote electrons from one d level to another d level of higher energy, corresponding to
a small difference and so light is absorbed in the visible region, the colour of the
transitional complex is dependent on how big the energy difference is between the two d
levels, this is in turn depends on the nature of the ligand, and the type of complex formed,
the colour change with the ligands used, the colour also depends on the number of ligands
and the shape of the complex.
The classification that Sc and Zn are not class as transitional elements is correct, however
they do show some limited characteristics to that of transitional element.
Source:
Concise inorganic chemistry (5th edition) J.D. Lee
Chemistry of the elements (2nd edition) N.N Greenwood and A. Earnshaw
Advanced inorganic Chemistry (5th edition) Cotton and Wilkinson
~ 2,101 words limited: 1500&X&2000 words
Keywords:
introduction three series elements situated periodic table following alkaline earth metals
described transition metal this term sometime extended include lanthanide actinide
elements there position periodic table between block block elements their properties
transitional between highly reactive metallic block which typically form ionic compounds
which largely covalent electrons added outer shell atom electrons added penultimate shell
explaining from electrons transitional typically have incompletely filled level however
group zinc group configuration complete shell compounds these typical show some
difference from other series they exhibit number characteristic properties which
distinguish them from other groups they metals such lustrous deformable have high
electrical thermal conductivities addition their melting boiling points tends high they
generally hard strong alloys with other metals most them display numerous oxidation
states vary step rather than usually case with those main group exhibit more than
oxidation state oxidation state shown transition maybe related electronic structure
calcium element preceding first transition electronic structure might expected that next
transitional would follow this trend electronic configuration this true except because
electron move result additional stability where orbital exactly half filled completely filled
structure state could have number both used bonding when both involved rest series
follows similar trend varying number used bonding varying states would result table
unparallel propensity forming ordination compounds with lewis base coordination
complex formed when lewis base ligand attached lewis acid acceptor means lone pair
where ligand composed atoms directly attached acceptor called donor atom type bonding
exemplified addition formed trihalides also basis much chemistry ability complexes
contrast only form complexes small highly charge vacant energy orbitals accept ions lone
pairs donated groups ligands general chemistry scandium element scandium properties
element soft slivery white display might expected following strongly electropositive
alkaline earth metal before metal proper scandium less electropositive than successors
electropositive successors always exist occurs classed class acceptors hard acid require
removal electron result ions configuration spectra impossible their colourless diamagnetic
similar some ways aluminium first three ionisation energies little less moderately high
standard electrode potentials quite reactive tarnish burn dioxygen giving oxides react
slowly cold water more rapidly water liberating forming either basic oxide hydroxide
appears exist definite compound basic oxide amphoteric like dissolves naoh liberating
naoh oxides hydroxides form salt acid react halogens forming trihalides resembling
halides fluoride insoluble halides diquescent very soluble like cacl anhydrous sccl differs
alcl sccl monomeric whilst alcl dimeric also sccl show friedel crafts catalytic salt
generally resemble that fluorides carbonates phosphates oxalates insoluble react
hydrogen heating highly conducting containing probably contain extra electron
conduction band true rest except since absorb more loose conducting power quite
stoichiometric having composition similar exact composition depends upon temperature
pressure hydrogen hydrides water liberating salt like ionic hydrides containing hydride
forms carbide when oxide heated carbon carbide ethyne carbide contains ions free
delocalises into conduction band giving some metallic conduction despite charge strong
tendency complexes large size readily that rest within both having coordination
octahedral shape most common donor atom particularly cheating ligands therefore strong
complexing agents such oxalic citric acetylacetone edta acetylacetone coordination
octahedral also bidentate ligand numbers four bidentate remaining unidentate giving
general chemistry zinc zinc show associated typical having complete available does
variable valency therefore cannot produce spectra many white whole smaller size
therefore posses greater polarizing power increasing chance covalency charge transfer
melting boiling point very explaining reactive copper ionisation energies suggest reverse
relatively soft compare maybe participate metallic slivery solid tarnish rapidly moist
dissolve dilute oxidizing acids oxidizing acids salts evolving mixture oxides amphoteric
prosperities soluble alkalis zincates those aluminates donor ligands reluctant bond since
there crystal field stabilization energy three coordinate rare occur largely four ordination
tetrahedral such where five coordinate common example terpyridyl trigonal bipyramid
shape several coordinate octahedral however very stable small size there example
involving bidentate atoms occupy ordination position forms basic acetate much beryllium
acetate however readily hydrolyses increase conclusion even though place first truly
limited proprieties melting boiling point point behave atypically complete does
participate explain only many lack ability wide range structural limited relate
introduction variable states does variable only since unparallel propensity base complex
formed attached acceptor means lone pair evidence limited extent tendency complex
despite almost restricted trivalent tendency know crystal fields splitting energy cannot
class classification correct additional note colourless compound explain configurations
respectively obtaining spectra possible largely colourless colour arise entirely different
cause incomplete shells free isolated gaseous five orbitals degenerate five same term
solution surrounded solvent molecule solution crystal lattice surrounding affect orbital
orbitals longer degenerate groups different partly possible promote level another level
higher corresponding small difference light absorbed visible region colour dependent
difference between levels turn depends nature type colour change used depends shape
classification class correct characteristics source concise inorganic edition edition
greenwood earnshaw advanced inorganic edition cotton wilkinson words words
Keywords General:
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