Transcript CLASSIFICATION OF METALS 2

ENVIRONMENTAL
CLASSIFICATION OF METALS
2--CLASSIFICATION OF METALS
Metals are elements that have a lustrous appearance, are
good conductors of electricity, and that act as cation in water
or when reacting with other chemicals.
H
Li Be
Na Mg
K Ca
Rb Sr
Cs Ba
Fr Ra
Sc
Y
La
Ac
Ti
Zr
Hf
Rf
C
Si
Ge
Sn
Pb
N
P
As
Sb
Bi
O
S
Se
Te
Po
F
Cl
Br
I
AT
He
Ne
Ar
Kr
Xe
Rn
Er
Ni
Pd
Pt
Cu
Ag
Au
Zn
Cd
Hg
B
Al
Ga
In
Tl
Nd Pm Sm Eu
Gd
Tb
Dy
Ho
Tm
Yb
Lu
Pu Am Cm Bk
Cf
Es Fm Md
No
Lr
V
Nb
Ta
Ha
Cr Mn
Mo Tc
W Re
Ce
Pr
Th
Pa
U
Fe
Ru
Os
Np
Co
Rh
Ir
Brown…………….alkali and alkaline earth metals
Red…………….....other metals
Blue…………….....metalloids
yellow fill………….most toxic metals
Black and green…..non-metals
1 - TRADITIONAL CHEMICAL
CLASSIFICATION OF METALS
Metals and metalloids comprise all
elements in the periodic table except:
Noble gases, H, B, C, N, O, F, P, S, Cl, Br,
I, and At.
METALLOIDS ARE SEMI METALS:
Si, Ge, As, Se, Sb, and Te
1.1. CHEMICAL CLASSIFICATION BASED ON METALLIGAND COMPLEX STABILITY CONSTANT DATA
• Proposed by Ahrlard et al., 1958
• Divides metals into:
– TYPE A metals,
– TYPE B metals, and
– Intermediate or BORDERLINE metals
• This classification is governed by the
number of electron in the outer shell
1.1.1. Type A Metal Cations (hard metals)
• Li+, Na+, K+, Be2+, Mg2+, Ca2+, Sr2+, Al3+, Sc3+,
La3+, Si4+, Ti4+, Zr4+, Th4+
•
•
•
•
Inert gas (do) electronic configuration
Spherical symmetry (hard ions)
Low polarizability
Preference of oxygen (O) and fluorine (F)
containing ligands over S and higher halides
Type A metal cations cont’d
• These metal ions may form insoluble complexes
with OH-, CO2-3, and PO3-4 (e.g. CaCO3; AlPO4)
• Complexes with OH- are more stable than those with
HS- or S2- because OH- displaces HS- and S2- in
aqueous solutions.
• Complexes with Cl-, Br-, and I- tend to be weak
• Complexes with H2O are more stable than those
with NH3 or CN-
Type A metal cations cont’d
• An electrostatic model approximately
explains the stability of type A metal-ligand
complexes—That is, the stability of type A
metal-ligand complexes is positively
correlated with the ionic index (Z2/r)
– Z = ionic charge
– r = radius
– Ionic Index is the ion’s propensity to form
ionic bonds
1.1.2. Type B Metal Cations
(SOFT METALS)
• Cu+, Ag+, Au+, Tl+, Ga+, Zn2+, Cd2+, Hg2+, Pb2+, Sn2+, Tl3+,
Au3+, In3+, Bi3+
They are metal cations with the following
electronic configuration:
– nd10 and nd10(n+1)S2
– Examples:
• Zn2+: Ar (3d10)
• Pb2+: Xe (4f145d106S2)
Type B metal cations (cont’d)
• They exhibit high polarizability
Unlike type A metal cations, here covalent bonding
plays a role in complex formation, and therefore, an
electrostatic model alone is unable to explain
stability relations.
• The stability of their complexes is affected by their
tendency to accept electrons (high en) from ligands
• Example: Zn (1.6)<Cd(1.7)<Hg(1.9)
And the stability complex with these metals are
generally in the same order as their en
Type B metal cations (cont’d)
• The electronegativity (en) of ligand donor atoms
and the stability (n) of formed complexes with
type B metal ions vary in the following order:
• Low en
High en
S I Br Cl N O F
• High n
Low n
Type B cations exhibit the following
complexation properties:
 Form more stable complexes than do type A
 Complex stability with halides decrease in the order
I- > Br- > Cl- > F (reverse of type A)
 Complexes with N-containing ligands are favored
over O-containing ligands

Examples: NH3 over H2O and CN- over OH-
 Complexes with S2- and HS- or organosulfides are
stable, and frequently, insoluble
 Form stable organometallic compounds in water
1.1.3. Intermediate or Borderline
Metal Cations
• Fall in this group, metal cations with -electronic
configuration ndX, with 0<x<10 (i.e. they have 1 to 9
outer shell electrons).
• Examples are:
• V2+, Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Ti3+, V3+, Cr3+,
Mn3+, Fe3+, Co3+
• They form complexes with all types of donor ligands
• The 2nd transition row in the periodic table shows
more type-B character than do those in the 1st row
Intermediate or borderline metal cations
(cont’d)
• Within borderline metals, type B character tend to
increase somewhat as one moves from left to right in
the periodic table
• Electrostatic factors play a role in the stability of
borderline metals
• The increase in stability comes from a stronger
electrostatic effect b/c of high Z2/r associated with
the decrease in ionic radius across the series
2. Environmental classification of
metals Based on Traditional
Chemical Classification
• Proposed by Nieboer and Richardson (1980)
• This classification is based on both
INDEX (Z2/r), and
– The COVALENT INDEX (X2m.r)
– The IONIC
• X2m.r is defined as the ability to accept efrom donor ligands, and where
» Xm= metal ion electronegativity (en)
» r = ionic radius
Environmental classification of metals
(cont’d)
 X2m.r is used as a parameter, which differentiates
between type A,
bordeline, and type B.
Ag+
Pb2+
Hg2+
4
Type B metals
Covalent
Index
2
X2
Fe2+
Cu2+ 2+
Co
Ni2+
Mn2+
Zn2+
3
m.r
1
Sn4+
Borderline metals
Mg2+
K+
Na+
4
Overall trend of stability of
Formed complexes
Al3+
Ca2+
Type A Metals
Ionic Index, Z2/r
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From the graph
• Type B are characterized by large X2m.r
• Type A have the smallest X2m.r
• Highly charged species will tend to be on the right end of the
diagram and these are species which tend to behave as
Bronsted acids (proton-donors).
Macronutrients (K+ and Ca2+) are type A and associated with Oelectron donors
•
•
Micronutrients (Mn, Cu, Zn) are intermediate and favored
ligands are O-N-S-containing electron-donors
• Type B = mostly toxic metals
• Overall, the toxicity increases in the order type A<
Intermediate<Type B.
In spite of limitations, concepts
discussed above do help
understand some of the features
of natural aqueous ion solution
chemistry.