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Unformatted text preview: NAME: NARELLE IAUMA
COURSE CODE: CH204
INTRODUCTION TO d-BLOCK ELEMENTS AND
COORDINATION CHEMISTRY OF d-BLOCK ELEMENTS.
The elements from the d-block are called transition metals due to their incomplete d-subshells
or that the cation produced have incomplete d-subshells. Not all elements from the d-block
are transition metals, group 12 elements (Zn, Cd, Hg and element 112) have complete dsubshells so we cannot call them transition metals. Apart from group 12 all other elements
from d-block are called transition metals because of their reaction with highly reactive
elements from the s-block that they formed ionic compounds and also, they have the covalent
types like the p-block elements.
The d-block elements are categorized into four series
4d-series Sc to 30Zn 21 Y to 48Cd 39 5d-series 57 La and 72Hf to 80Hg 6d-series 89 Ac Section 1: The properties of d-block elements.
a. The different series have their own electronic configuration; as the 3d-series from Sc
to Zn, the electrons go into the 3d orbital. Example; 21Sc = [Ar] 4s2 3d1 and
22Ti = [Ar] 4s 3d . For the 4d-series, the electrons then go into the 4d-orbital.
Example; 39Y = [Kr] 5s2 4d1 and 40Zr = [Kr] 5s2 4d2.
b. They have the metallic character They are good conductors of electricity and heat They are strong, hard and ductile With other metals, they can form alloys They have metallic lustre
c. They have various oxidation states
Transition elements have different oxidation states that they come in with, and the
states of oxidation differ in units of one. For instance; Fe2+ and Fe3+. For the next 10
element (Sc to Zn) the electrons are successfully added in the d-orbital, but for Cr and
Cu they are both half-filled or both have fully filled d-orbital. For example; 21Sc have
the electron configuration of [Ar] 4s2 3d1 and the oxidation states are II and III.
d. Transition metals can form compounds/ions that show colours.
These group of elements can form coloured compounds/ions due to the white light
that is reflected or transmitted that strikes them.
e. Atoms and ions sizes
Going from left to right across rows from the periodic table, the covalent radius of
transition metals decreases. f. The melting and boiling point of transition metals are very high and that it increases
down the group.
g. Transition metals formed coordination compounds.
Transition metals have empty d-orbital that they accommodate by forming
h. Magnetic properties
Transition metals form two types of compounds; paramagnetic compounds and
diamagnetic compounds. Paramagnetic compounds are compounds which have
unpaired electrons and diamagnetic compounds are those with paired electrons. The
spin only magnetic moment can be calculated using the formular below.
μ = √ n ( n+2 )
where n = # of unpaired electrons
i. Transition metals have catalytic properties
MnO2 – by decomposing KClO3 giving O2
j. Transition metals have the tendency in forming non-stoichiometric compounds.
Transition metals sometime can form compounds that have infinite structures and
proportions (non-stoichiometric). For instance, selenium and vanadium forming series
of compounds that range from: VSe0.98
VSe1.2 and VSe1.2
Section 2: coordination chemistry
a. Simple salts
Acid and base react to form salt and water
NaOH + HCl
NaCl + H2O
b. Addition/molecular compounds
These comes in two types, double salts /lattice compounds and complex/coordination
- Double salts/lattice compounds; have the below characteristics In crystalline state, they exist as such They dissociate into ions when dissolving in water, and the ions formed
appeared as double salts do when in individual components. FeSO4. (NH4)2SO4.6H2O Fe2+(aq) + 2NH4+(aq) +2SO42-(aq) + 6H2O Mohr’s salt
- Complex compounds: this are compounds that forms complex ion
E.g: Fe(CN)2 + 4KCN
4K+ + [Fe(CN)6]4- Only the combination of potassium and ferrocyanide ion are formed.
Ligands are Lewis base/electron paired donor and they come with lone pairs of electrons.
They donate one or more electrons to the central metal ion. E.g H2O which have 2 lone pairs.
Section 3: coordination compounds formation; Werner theory
From the Werner theory, Alfred Werner concluded that metals shows two types of valency in
coordination complexes. The primary valency and secondary valency. - - Primary valency: it is the oxidation state of the metal ion. (metals always gives
electrons). E.g; Co(NH3)6]Cl3 the complex existed as [Co(NH3)6]3+ and 3Cl-, where
the 3 negative chloride ion balances the complex Co-ammine, thus the primary
valency is +3.
Secondary /auxillary valency: it is the number of ligands surrounding the central
atom/ion. Coordination compounds complex are separated into three(3) types. 1.
Neutral [Pt(NH3)2Cl2], Cationic [Cr(H2O)4Cl2]+ and Anionic [Fe(CN)6]3-. An example of a coordination complex, in relation to Werner’s theory Section 4: effective atomic number by Sidgwick’s
Sidgwick stated that through bonding, the ligands give some electrons to the central atom.
The effective atomic number is then the overall number of electrons that the central atom
contains with those that ligands added through bonding. The effective atomic number is equal
the atomic number of inert gas.
Example: [Fe(CN)6]4Fe atomic # = 26
Fe2+ = 26-2 = 24 electrons
Electrons donated by 6 (CN) = 6 × 2 = 12
EAN of Fe(II) in [Fe(CN)6]4- = 24 + 12 = 36
Thus the compound obeys the EAN rule.
Exclusions to EAN rule
Some complexes do not follow the EAN rule because they have more than one coordination
number. Given some examples below; Section 5: The eighteen (18) electron rule In complex/coordination compounds, the total number of electrons in the valence shell and
that given by ligands must be equal the number of electrons in valence orbital and that is 18.
Therefore, known as the eighteen-electron rule.
Example 1: Cr(Co)6
Oxidation number of Cr = 0
Cr have valence electron of = 6
# of electrons donated by ligand = 12 (2×6)
Total = 18 electrons
Thus, the compound above satisfies the eighteen-electron rule and is stable. Example 2: Ni(Co)4
Ni have the valence electrons = 2
# of electrons donated by ligands = 8 (2×)
Total = 10 electrons
Therefore, there is failure for the 18-electron rule and the complex is not stable.
Any complex that obeys the EAN rule does follow the eighteen-electron rule.
Section 6: Ligands classification
Ligand always comes with lone pairs. There are various types of ligands;
Monodentate ligands E.g; H2O.NH3 and C5H5N
Bidentate Ligands E.g; ethylenediamine(en). Carbonato(Co-23)
Tridentate ligand E.g Diethylenetriamine (Dien)
Tetradentate Ligand E.g triethylene tetramine (trien)
Pentadentate ligand E.g ethylene diamine triacetate
Hexadentate ligand E.g ethylenediamine tetra acetic acid anion.
Coordination chemistry of d-block elements
There are rules that had to be followed when naming complex compounds
1. Naming of ligands
When given a complex compound, the ligands are named first and in alphabetical
order before the central atom. If there are more than one ligand in the complex, then
the Anionic (negative) ligands is named first followed by Neutral ligands then
cationic(positive) ligands. For negative ligands, the anion names ends with e is
replaced by-o, for instance, SO2-3 the name is Sulphito. When naming neutral ligands,
there are no systematic names. For instance, H2O (Aqua).
2. Ambidentate ligands
These are types of ligands that are coordination of two different site. Example; (NH4)3[Cr(NCS)6] – Ammonium hexaisothiocyanatochromate(III)
Below are some examples of complex compounds and name given;
a. [Cr(NH3)(H2O)3]Cl3 ; Triaminetriaquachromium(III) chloride
b. K4[Fe(CN)6]; potassium hexacynoferrate(II)
Naming of bridging ligands
The prefix μ indicates bridging ligands Chelating agents: these are agents in which its molecules can form many bonds with a single
metal ion in that a ring is form. For instance; ethylenediamine which one of its single
molecule can form two bonds to Nickel(II) a transition metal.
EDTA is a chelating agent that is of economic importance. It is also a versatile chelating
agent that can form four/six bonds to a metal ion. Because this chelating agent can form
complexes with calcium and magnesium it is then used in detergents and soaps. EDTA is
used in food industry as stabilizing agent.
Factors affecting the formation of chelation
1. The chelating group basic strength; The basic strength of chelating agent increases
with increasing stability of chelate complexes.
2. The chelating group nature of atoms donating; ligands that have atoms that can
donate, form stable complex with soft acid.
3. Their ring size; the size of the ring matters as the most stable ring are those with 5 or
6 member rings.
Stability of coordination compound Example:[Co(NH3)6] ...
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