The Group 12 Elements
“Read in the name your God who created “
http://kimia.unp.ac.id
)I(
Inorganic Chemistry 3
)I(
Miftahul Khair, M.Sc ([email protected])
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Intro
Mercury
Found in ancient Chinese and Indian writings, and Egyptian
specimens date to about 1500 B.C.
From 200 B.C., a mine in Spain supplied mercury (as
mercury(II) sulfide) to the Roman Empire.
Roman convicts : a sentence to the mercury mine
1570: Mercury could be used to extract silver from silvercontaining ores,
The solution of silver in mercury was separated from the
solid residue and then heated strongly—the mercury
vaporized and dissipated into the atmosphere !
Even today, this primitive and environmentally dangerous
method is being used, this time to extract gold from gold
deposits in the Amazon basin.
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Group Trends
Chemistry difference with the transition
metals :
melting points
°C
zinc and
cadmium
transition
metals
419 and 321
1000
•have filled d orbitals
•compounds are white,
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Zinc and Cadmium
•chemically reactive
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Extraction of Zinc
Steps:
Source : ZnS, (mineral sphalerite/ zinc blende),
1. Roasting ZnS in air
2. Reduce with Coke
The hot gaseous zinc metal is rapidly
cooled by spraying it with molten lead.
The two metals are then easily separated,
because the liquid metals are immiscible.
Density zinc = 7 g/cm–3
Density lead =11 g/cm–3,
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Zinc
•anticorrosion coating for iron galvanizing
(formation of a protective layer in damp air)
Oxide layer, then the basic carbonate, Zn2(OH)2CO3
layer
. The advantage of zinc plating is that the zinc will be
oxidized in preference to the iron, even when some of
the iron is exposed
See more negative reduction potential of the zinc:
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Zinc Salts
•soluble in water, these solutions contain the colorless
[Zn(OH2)6]2•the solid salts are often hydrated : Zn(NO3)2.6H2O. Etc
Solutions of zinc salts are acidic due to a multistep hydrolysis:
Addition of hydroxide :
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ZnCl2 is used as a flux in soldering
solderin
-depend on the ability of the compound to function
as a Lewis acid.
In soldering, the oxide film on the surfaces to be
joined must be removed; otherwise, the solder will
not bond to these surfaces.
Above 275 C, ZnCl2 melts and removes the oxide
film by forming covalently bonded complexes with
the oxide ions.
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Zinc Oxide
obtained by :
ZnO : yellow hot white cold
thermochromism
results from the loss of some oxygen from the
lattice, leaving it with an excess negative charge.
The excess negative charge (electrons) can be moved
through the lattice by applying a potential difference;
thus, this oxide is a semiconductor.
White again when cooled, because the oxygen that
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was lost during heating returns to the crystal lattice.
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Cadmium Sulfide
CdS : intense yellow pigment
Preparation :
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The NiCad Battery
rechargeable
Discharge :
Charging : the reverse reactions
Ni–Cd batteries contain between 6% (for industrial batteries)
and 18% (for consumer batteries) cadmium, which is
a toxic heavy metal
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Optional : LithiumLithium-ion Batteries
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Mercury
•the weakest metalli c bonding liquid metal at 20oC
•toxic metal vapor can be absorbed through the lungs,
•M.p –39oC and b.p 357oC.
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Extraction of Mercury
•The only ore : HgS (mineral cinnabar) occasionally found as
the free liquid metal.
•readily extracted from the sulfide ore by heating it in air :
•used in thermometers, barometers, electrical switches,
and mercury arc lights
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Amalgam : Solutions of other metals in mercury.
Sodium amalgam and zinc amalgam are used as
laboratory reducing agents,
Dental amalgam (Hg mixed with one or more of the
metals silver, tin, and copper),
Reasons : 1. expands slightly as the amalgam forms,
2. does not fracture easily under the extreme
localized pressures
3. low coefficient of thermal expansion
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Mercury(II) Compounds
Virtually all mercury(II) compounds utilize covalent bonding
Mercury(II) chloride
Mercury(II) oxide is thermally unstable
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Mercury(I) Compounds
•Unique for two mercury ions are united by a single covalent bond
•Hg2Cl2, and Hg2(NO3)2 exist, but
compounds with other common anions, such as sulfide, have never
been synthesized, because :
low : little tendency for the mercury(I)
ion to disproportionate into the
mercury(II) ion and mercury
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Mercury(IV) Fluoride
HgF4
•can only be synthesized at 4 K
and decompose on warming
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Biological Aspects
This group contains one essential element
(zinc) and two very toxic elements.
Zinc
most crucial elements in our diet.
Over 200 zinc enzymes have been identifi ed in living
organisms.
Hydrolases : catalyze the hydrolysis of P—O—P, P—O—C,
and C—O—C bonds.
Zinc deficiency : fatigue, lethargy, diminished disease resistance).
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What makes zinc such a useful ion?
1. Zinc is widely available in the environment.
2. The zinc ion is a strong Lewis acid, and zinc functions as a
Lewis acid in enzymes.
3. Zinc, unlike many other metals, prefers tetrahedral
geometries, a key feature of the metal site in most zinc
enzymes.
Five- and six-coordinate geometries are also available,
making transition states involving these coordination
numbers possible.
4. The zinc ion has a d10 electron confi guration, so there is no
crystal field stabilization energy associated with exact
geometries as there are with the transition metals.
5. The zinc ion is completely resistant to redox changes at
biological potentials thus, its role cannot be affected by
changing redox potentials in the organism.
6. The zinc ion undergoes extremely rapid ligand exchange,
facilitating its role in enzymes.
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The Toxicity of Cadmium
Toxic, 200 ppm causes severe damage on kidney,
Cigarette smokers absorb significant levels of cadmium from
tobacco smoke.
NiCad batteries are major waste disposal problem
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The Many Hazards of Mercury
hazardous because of high vapor pressure.
Hg vapor is absorbed in the lungs, dissolves in the blood, and
is then carried to the brain, where irreversible damage to the
central nervous system results.
Hg metal is also slightly water-soluble, again a result of its
very weak metallic bonding.
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Buyat Bay Hg and Arsenic Pollution
2004, local people in the area complained
several unusual health problems which
further suspected Newmont's for
breaching the mining waste level
regulation to had contaminated the area
with hazardous materials
The Indonesian activist group on
environment, WALHI, claimed that
Newmont has been dumping 2,000 tonnes
of mine waste into the bay daily
A legal case between the government of
Indonesia versus one of the company's
top executive is still ongoing.
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Chemistry Department