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Title: Chemistry/Elements/Silicon - Lenntech: Silicon Physical data, chemical properties, and health effects.
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Silicon Data tables and historic information.
| Silicon_Chemistry_Primer Review of silicon and silicone chemistry including properties and types of materials that can be made.
| USGS_Minerals_Information__Silicon Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
| Visual_Elements__Silicon General and physical information, source, uses, biological role, key isotopes, and ionisation energies.
| WebElements__Silicon Extensive information on history, uses, occurrence, compounds, and properties of the element.
| Wikipedia__Silicon Properties of the element, including its history, applications, and characteristics.
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Silicon (Si) - Chemical properties, Health and Environmental effects
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Chemical properties of silicon
- Health
effects of silicon -
Environmental effects of silicon
Atomic number
14
Atomic mass
28.0855 g.mol -1
Electronegativity
according to Pauling
1.8
Density
2.33 g.cm -3 at 20 °C
Melting point
1410 °C
Boiling point
3265 °C
Vanderwaals
radius
0.132 nm
Ionic radius
0.271 (-4) nm ; 0.041(+4)
Isotopes
5
Electronic
shell
[Ne] 3s23p2
Energy of
first ionisation
786.3 kJ.mol -1
Energy of
second ionisation
1576.5 kJ.mol -1
Energy of
third ionisation
3228.3 kJ.mol -1
Energy of
fourth ionisation
4354.4
kJ.mol -1
Discovered by
Jons
Berzelius in 1823
Silicon
Silicon is
the most abundant electropositive element in The Earth’s crust. It’s
a metalloid with a marked metallic luster and very brittle. It is
usually tetravalent in its compounds, although sometimes its bivalent,
and it’s purely electropositive in its chemical behaviour. Moreover,
pentacoordinated and hexacoordinated silicon compounds are also known.
Natural silicon contains 92.2% of the isotope 28, 4.7% of silicon
29 and 3.1% of silicon 30. Apart from those stable natural isotopes,
various radiactive artificial isotopes are known. Elemental silicon has
the physical properties of metalloids, similar to the ones or germanium,
situated under it in the group IV of the periodic
table. Silicon is an
intrinsic semiconductor in it’s purest form, although the intensity of
its semiconduction is highly increased by introducing small quantities
of impurities. Silicon is similar to metals in its chemical behaviour.
It’s almost as electropositive as tin and much more positive
than germanium or lead. According to this metallic character, it forms
tetrapositive ions and various covalent compounds; it appears as a
negative ion only in a few silicides and as a positive constituent of
oxyacids or complex anions.
It forms various series of hydrides, various halides (many of
which contain silicon-silicon bounds) and many series of compounds which
contain oxygen, which can have ionic or covalent properties.
Applications
Silicon is the principal component of glass, cement, ceramics, most
semiconductor devices, and silicones, the latter a plastic substance
often confused with silicon. Silicon is also an important constituent of
some steels and a major ingredient in bricks. It is a refractory
material used in making enamels and pottery.
Elemental raw silicon and its intermetallic compounds are used as
alloy integrals to provide more resistance to the aluminium,
magnesium,
copper and other metals. Metallurgic silicon with 98-99% purity is used
as raw material in the manufacture of organosilicic and silicon resins,
seals and oils. Silicon chips are used in integrated circuits.
Photovoltaic cells for direct conversion of solar energy use thin cut
slices of simple silicon crystals of electronic grade. Silicon dioxide
is used as raw material to produce elemental silicon and silicon
carbide. Big silicon crystals are used for piezoelectric glasses. Melted
quartz sands are transformed in silicon glasses which are used in
laboratories and chemical plants, as well as in electric insulators. A
colloidal dispersion of silicon in water is used as a coating agent and
as ingredient for certain enamels.
It
is known that silicon forms compounds with 64 out of the 96 stable
elements and possibly form silicides with other 18 elements. Appart from
metallic silicides, which are used in big quantities in metallurgy, it
forms important commonly used compounds with hydrogen,
carbon, halogens, nitrogen,
oxygen and sulphur. Moreover, many useful organosilicic
by-products.
Silicon in the environment
Silicon is found in many dioxide forms and in uncountable
variations from the natural silicates.
The silicon is much more abundant than any other element, apart
from the oxygen. It constitutes 27,72% of the solid Earth’s crust,
while the oxygen constitutes 46,6%, and the next element after silicon,
aluminium, is found in a 8,13%.
Sand is used as source of the silicon produced commercially. A few
siliate minerals are mined, e.g. talc and mica. Other mined silicates
are feldspars, nephenile, olivine, vermiculite, perlite, kaolinite, etc.
At the other extreme there are forms of silica so rare that they are
desirable for this reason alone: gemstone opal, agate and rhinestone.
Health
effects of silicon
Silicon concentrates in no particular organ of the body but is found
mainly in in connective tissues and skin. Silicon is non-toxic as the
element and in all its natural forms, nameli silica and silicates, which
are the most abundant.
Elemental
silicon is an inert material, which appears to lack the property of
causing fibrosis in lung tissue. However, slight pulmonary lesions have
been reported in laboratory animals from intratracheal injections of
silicon dust. Silicon dust has little adverse affect on lungs and does
not appear to produce significant organic disease or toxic effects when
exposures are kept beneath exposure limits. Silicon may cause chronic
respiratory effects. Crystalline silica (silicon dioxide) is a potent
respiratory hazard. However, the likelihood of crystalline silica
generation during normal processing
is very remote. LD50 (oral)- 3160 mg/kg. (LD50:
Lethal dose 50. Single dose of a substance that causes the death of 50%
of an animal population from exposure to the substance by any route
other than inhalation. Usually expressed as milligrams or grams of
material per kilogram of animal weight.)
Silicon
crystalline irritates the skin and eyes on contact.
Inhalation will cause irritation to the lungs and mucus membrane.
Irritation to the eyes will cause watering and redness. Reddening,
scaling, and itching are characteristics of skin inflammation.
Lung
cancer is associated with occupational exposures to crystalline silica
specifically quartz and cristobalite. An exposure-response relationship
has been reported in studies of miners, diatomaceous earth workers,
granite workers, pottery workers, refractory brick workers, and other
workers
Several
epidemiological studies have reported statistically significant numbers
of excess deaths or cases of immunologic disorders and autoimmune
diseases in silica-exposed workers. These diseases and disorders include
scleroderma,
rheumatoid arthritis, systemic lupus erythematosus, and sarcoidosis.
Recent epidemiological studies have reported statistically significant
associations of occupational exposure to crystalline
silica with renal diseases and subclinical renal changes
Crystalline
silica may affect the immune system, leading to mycobacterial infections
(tuberculous and nontuberculous) or fungal, especially in workers with
silicosis
Occupational
exposure to breathable crystalline silica is associated with bronchitis,
chronic
obstructive pulmonary disease (COPD) and emphysema. Some epidemiologic studies suggest that
these health effects may be less frequent or absent in nonsmokers.
Effects of silicon on the environment
No
negative environmental effects have been reported.
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