Hydrogen
Hydrogen is a chemical element with chemical H and
atomic number 1. With an atomic weight of 1.00794 u (u for hydrogen-1),
hydrogen is the lightest element and its monatomic form (H1) is the most
abundant chemical substance, constituting roughly 75% of the Universe's
baryonic mass. Non-remnant stars are mainly composed of hydrogen in its
plasma state.
At standard temperature and pressure, hydrogen is
a colorless, odorless, tasteless, non-toxic, nonmetallic, highly
combustible diatomic gas with the molecular formula H2. Most of the
hydrogen on Earth is in molecules such as water and organic compounds
because hydrogen readily forms covalent compounds with most non-metallic
elements.
Hydrogen plays a particularly important role in
acid–base chemistry with many reactions exchanging protons between
soluble molecules. In ionic compounds, it can take a negative charge (an
anion known as a hydride and written as H−), or as a positively charged
species H+. The latter cation is written as though composed of a bare
proton, but in reality, hydrogen cations in ionic compounds always occur
as more species that are complex.
The most common isotope of
hydrogen is protium (name rarely used, symbol 1H) with a single proton
and no neutrons. As the simplest atom known, the hydrogen atom has been
of theoretical use. For example, as the only neutral atom with an
analytic solution to the Schrödinger equation, the study of the
energetic and bonding of the hydrogen atom played a key role in the
development of quantum mechanics.
Hydrogen gas was first
artificially produced in the early 16th century, via the mixing of
metals with acids. In 1766–81, Henry Cavendish was the first to
recognize that hydrogen gas was a discrete substance, and that it
produces water when burned, a property which later gave it its name: in
Greek, hydrogen means "water-former".
Industrial production is
mainly from the steam reforming of natural gas, and less often from more
energy-intensive hydrogen production methods like the electrolysis of
water. Most hydrogen is employed near its production site, with the two
largest uses being fossil fuel processing (e.g.,hydrocracking) and
ammonia production, mostly for the fertilizer market.
Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks.
Hydrogen
gas (dihydrogen or molecular hydrogen) is highly flammable and will
burn in air at a very wide range of concentrations between 4% and 75% by
volume. The enthalpy of combustion for hydrogen is −286 kJ/mol:
2 H2(g) + O2(g) → 2 H2O(l) + 572 kJ (286 kJ/mol)
Hydrogen
gas forms explosive mixtures with air if it is 4–74% concentrated and
with chlorine if it is 5–95% concentrated. The mixtures may be ignited
by spark, heat or sunlight. The hydrogen autoignition temperature, the
temperature of spontaneous ignition in air, is 500 °C (932 °F). Pure
hydrogen-oxygen flames emit ultraviolet light and with high oxygen mix
are nearly invisible to the naked eye, as illustrated by the faint plume
of the Space Shuttle Main Engine compared to the highly visible plume
of a Space Shuttle Solid Rocket Booster. The detection of a burning
hydrogen leak may require a flame detector; such leaks can be very
dangerous. Hydrogen flames in other conditions are blue, resembling blue
natural gas flames. The destruction of the Hindenburg airship was an
infamous example of hydrogen combustion; the cause is debated, but the
visible orange flames were the result of a rich mixture of hydrogen to
oxygen combined with carbon compounds from the airship skin.
H2
reacts with every oxidizing element. Hydrogen can react spontaneously
and violently at room temperature with chlorine and fluorine to form the
corresponding hydrogen halides, chloride and hydrogen fluoride, which
are also potentially dangerous acids.
Fluorine
Fluorine is the chemical element with symbol F and
atomic number 9. It is the lightest halogen and has a single stable
isotope, fluorine-19. At standard pressure and temperature, fluorine is a
pale yellow gas composed of diatomic molecules, F2. Fluorineis
the most electronegative element. It is also the most reactive of all
the elements, requiring great care in handling. The compounds of
fluorine are called fluorides.
In stars, fluorine is rare
compared to other light elements. In Earth's crust, fluorine is the
thirteenth-most abundant element. Fluorine's most important mineral,
fluorite, was first formally described in 1529 in the context of
smelting. The mineral's name derives from the Latin verb fluo, meaning
"flow", because fluorite was added to metal ores to lower their melting
points. Suggested as a chemical element in 1811, fluorine was named
after the source mineral. The dangerous element resisted many attempts
to isolate it, but in 1886, French chemist Henri Moissan succeeded. His
method of electrolysis remains the industrial production method for
fluorine gas. The largest use of elemental fluorine, uranium enrichment,
was developed during the Manhattan Project.
Oxygen
Oxygen is a chemical element with symbol O and
atomic number 8. Its name derives from the Greekroots ὀξύς (oxys)
("acid", literally "sharp", referring to the sour taste of acids) and
-γόνος (-gοnos) ("producer", literally "begetter"), because at the time
of naming, it was mistakenly thought that all acids required oxygen in
their composition. At standard temperature and pressure, two atoms of
the element bind to form dioxygen, a colorless, odorless, tasteless
diatomic gas with the formula O2. This substance is an important part of
the atmosphere, and is necessary to sustain most terrestrial life.
Oxygen
is a member of the halogen group on the periodic table and is a highly
reactive nonmetallic element that readily forms compounds (notably
oxides) with most elements except the noble gases Helium and Neon.
Oxygen is a strong oxidizing agent and only fluorine has greater electro
negativity. By mass, oxygen is the third-most abundant element in the
universe, after hydrogen and helium and the most abundant element by
mass in the Earth's crust, making up almost half of the crust's mass.
Oxygen is too chemically reactive to remain a free element in Earth's
atmosphere without being continuously replenished by the photosynthetic
action of living organisms, which use the energy of sunlight to produce
elemental oxygen from water. Free elemental O2 only began to accumulate
in the atmosphere about 2.5 billion years ago (see Great oxygenation
event) about a billion years after the first appearance of these
organisms. Diatomic oxygen gas constitutes 20.8% of the volume of air.
Oxygen
was discovered independently by Carl Wilhelm Scheele, in Uppsala, in
1773 or earlier, and Joseph Priestley in Wiltshire, in 1774, but
Priestley is often given priority because his work was published first.
The name oxygen was coined in 1777 c, whose experiments with oxygen
helped to discredit the then-popular phlogiston theory of combustion and
corrosion. Oxygen is produced industrially by fractional distillation
of liquefied air, use of zealots with pressure-cycling to concentrate
oxygen from air, electrolysis of water and other means. Uses of
elemental oxygen include the production of steel, plastics and textiles,
brazing, welding and cutting of steels and other metals ,rocket
propellant, oxygen therapy and life support systems in aircraft,
submarines, spaceflight and diving.
Argon
Argon is a chemical
element with symbol Ar and atomic number 18. It is in-group 18 of the
periodic tableand is a noble gas. Argon is the third most common gas in
the Earth's atmosphere, at 0.93% (9,300 ppm), making it approximately
23.8 times as abundant as next most common atmospheric gas, carbon
dioxide(390 ppm), and more than 500 times as abundant as the next most
common noble gas, neon (18 ppm). Nearly all of this argon is radiogenic
argon-40 derived from the decay of potassium-40 in the Earth's crust. In
the universe, argon-36 is by far the most common argon isotope, being
the preferred argon isotope produced by stellar nucleosynthes is in
supernovas. The name "argon" is derived from the Greek word αργον,
neuter singular form of αργος meaning "lazy" or "inactive", as a
reference to the fact that the element undergoes almost no chemical
reactions. The complete octet (eight electrons) in the outer atomic
shell makes argon stable and resistant to bonding with other elements.
Its triple point temperature of 83.8058 K is a defining fixed point in
the International Temperature Scale of 1990. Argon is produced
industrially by the fractional distillation of liquid air. Argon is
mostly used as an inert shielding gas in welding and other
high-temperature industrial processes where ordinarily non-reactive
substances become reactive; for example, an argon atmosphere is used in
graphite electric furnaces to prevent the graphite from
burning.
Argon gas also has uses in incandescent and fluorescent lighting, and
other types of gas discharge tubes. Argon makes a distinctive blue-green
gas laser. Argon has approximately the same solubility in water as
oxygen, and is 2.5 times more soluble in water than nitrogen. Argon is
colorless, odorless, and nontoxic as a solid, liquid, and gas. Argon is
chemically inert under most conditions and forms no confirmed stable
compounds at room temperature. Although argon is a noble gas, it has
been found to have the capability of forming some compounds. For
example, the creation of argon fluorohydride (HArF), a marginally stable
compound of argon with fluorine and hydrogen, was reported by
researchers at the University of Helsinki in 2000.[2] Although the
neutral ground-state chemical compounds of argon are presently limited
to HArF, argon can formclathrates with water when atoms of it are
trapped in a lattice of the water molecules. Argon-containing ions and
excited state complexes, such as ArH+ and ArF, respectively, are known
to exist. Theoretical calculations have predicted several argon
compounds that should be stable, but for which no synthesis routes are
currently known.
Carbon
Carbon (from Latin: carbo
"coal") is the chemical element with symbol C and atomic number 6. As
a member of group 14 on the periodic table, it is nonmetallic and
tetravalent—making four electrons available to form covalent chemical
bonds. There are three naturally occurring isotopes, with 12C and 13C
being stable, while 14C is radioactive, decaying with a half-life of
about 5,730 years. Carbon is one of the few elements known since
antiquity. There are several allotropes of carbon of which the best
known are graphite, diamond, and amorphous carbon. The physical
properties of carbon vary widely with the allotropic form. For example,
diamond is highly transparent, while graphite is opaque and black.
Diamond is the hardest naturally- occurring material known, while
graphite is soft enough to form a streak on paper (hence its name, from
the Greek word "γράφω" which means "to write"). Diamond has a very low
electrical conductivity, while graphite is a very good conductor. Under
normal conditions, diamond, carbon annotates and graphene have the
highest thermal conductivities of all known materials.
All carbon
allotropes are solids under normal conditions with graphite being the
most thermodynamically form. They are chemically resistant and require
high temperature to react even with oxygen. The most common oxidation
state of carbon in inorganic compounds is +4, while +2 is found in
carbon monoxide and other transition metal carbonyl complexes. The
largest sources of inorganic carbon are limestone’s, dolomites and
carbon dioxide, but significant quantities occur in organic deposits of
coal, peat, oil and methane catharses. Carbon forms more compounds than
any other element, with almost ten million pure organic compounds
described to date, which in turn are a tiny fraction of such compounds
that are theoretically possible under standard conditions. Carbon is
the 15th most abundant element in the Earth's crust, and the fourth most
abundant element in the universe by mass after hydrogen, helium, and
oxygen. It is present in all known life forms, and in the human body
carbon is the second most abundant element by mass (about 18.5%) after
oxygen. This abundance, together with the unique diversity of organic
compounds and their unusual polymer-forming ability at the temperatures
commonly encountered on Earth, make this element the chemical basis of
all known life.
Sulfur
Sulfur or sulphur (British
English; see spelling below) is a chemical element with symbol S and
atomic number 16. It is an abundant, multivalent non-metal. Under normal
conditions, sulfur atoms form cyclic octatomic molecules with chemical
formula S8. Elemental sulfur is a bright yellow crystalline solid when
at room temperature. Chemically, sulfur can react as either an oxidant
or reducing agent. It oxidizes mostmetals and several nonmetals,
including carbon, which leads to its negative charge in most
organosulfur compounds, but it reduces several strong oxidants, such as
oxygen and fluorine. Sulfur occurs naturally as the pure element (native
sulfur) and as sulfide and sulfate minerals. Elemental sulfur crystals
are commonly sought after by mineral collectors for their distinct,
brightly colored polyhedronshapes. Being abundant in native form, sulfur
was known in ancient times, mentioned for its uses inancient India,
ancient Greece, China and Egypt. Fumes from burning sulfur were used as
fumigants, and sulfur-containing medicinal mixtures were used as balms
and antiparasitics. Sulfur is referred to in theBible as brimstone (burn
stone) in English,
with this name still used in several
nonscientific tomes. It was needed to make the best quality of black
gunpowder. In 1777, Antoine Lavoisier helped convince the scientific
community that sulfur was a basic element, rather than a compound.
Elemental sulfur was once extracted from salt domes where it sometimes
occurs in nearly pure form, but this method has been obsolete since the
late 20th century. Today, almost all elemental sulfur is produced as a
byproduct of removing sulfur-containing contaminants from natural gas
and petroleum. The element's commercial uses are primarily in
fertilizers, because of the relatively high requirement of plants for
it, and in the manufacture of sulfuric acid, a primary industrial
chemical. Other well-known uses for the element are in matches,
insecticides and fungicides. Many sulfur compounds are odoriferous, and
the smell of odorized natural gas, skunk scent, grapefruit, and garlic
is due to sulfur compounds. Hydrogen sulfideproduced by living organisms
imparts the characteristic odor to rotting eggs and other biological
processes. Sulfur is an essential element for all life, and is widely
used in biochemical processes. In metabolic reactions, sulfur compounds
serve as both fuels (electron donors) and respiratory
(oxygen-alternative) materials (electron acceptors).
Sulfur in organic
form is present in the vitamins biotin and thiamine, the latter being
named for the Greek word for sulfur. Sulfur is an important part of many
enzymes and in antioxidant molecules like glutathione and thioredoxin.
Organically bonded sulfur is a component of all proteins, as the amino
acids cysteine and methionine. Disulfide bonds are largely responsible
for the mechanical strength and insolubility of the protein keratin,
found in outer skin, hair, and feathers, and the element contributes to
their pungent odor when burned.
Sodium
Sodium is a chemical element with the symbol Na (from Latin:
natrium) and atomic number 11. It is a soft, silvery-white, highly
reactive metal and is a member of the alkali metals; its only stable
isotope is Na. The free metal does not occur in nature, but instead must
be prepared from its compounds; it was first isolated by Humphry Davy
in 1807 by the electrolysis of sodium hydroxide. Sodium is the sixth
most abundant element in the Earth's crust, and exists in numerous
minerals such as feldspars, sodalite and rock salt. Many salts of sodium
are highly water-soluble, and their sodium has been leached by the
action of water so that chloride and sodium are the most common
dissolved elements by weight in the Earth's bodies of oceanic water.
Many sodium compounds are useful, such as sodium hydroxide (lye) for
soapmaking, and sodium chloride for use as a deicing agent and a
nutrient (edible salt). Sodium is an essential element for all animals
and some plants. In animals, sodium ions are used against potassium ions
to build up charges on cell membranes, allowing transmission of nerve
impulses when the charge is dissipated. The consequent need of animals
for sodium causes it to be classified as a dietary inorganic
macro-mineral.
Characteristics
Physical Sodium at standard
temperature and pressure is a soft metal that can be readily cut with a
knife and is a good conductor of electricity. Freshly exposed, sodium
has a bright, silvery luster that rapidly tarnishes, forming a white
coating of sodium hydroxide and sodium carbonate. These properties
change at elevated pressures: at 1.5 Mbar, the color changes to black,
then to red transparent at 1.9 Mbar, and finally clear transparent at 3
Mbar. All of these allotropes are insulators and electrides. When
sodium or its compounds are introduced into a flame, they turn it
yellow, because the excited 3s electrons of sodium emit a photon when
they fall from 3p to 3s; the wavelength of this photon corresponds to
the D line at 589.3 nm. Spin-orbit interactions involving the electron
in the 3p orbital split the D line into two; hyperfine structures
involving both orbitals cause many more lines.
Chemical Sodium is
generally less reactive than potassium and more reactive than lithium.
Like all the alkali metals, it reacts exothermically with water, to the
point that sufficiently large pieces melt to a sphere and may explode;
this reaction produces caustic sodium hydroxide and flammable hydrogen
gas. When burned in dry air, it mainly forms sodium peroxide as well as
some sodium oxide. In moist air, sodium hydroxide results. Sodium metal
is highly reducing, with the reduction of sodium ions requiring −2.71
volts but potassium and lithium have even more negative potentials.
Hence, the extraction of sodium metal from its compounds (such as with sodium chloride) uses a significant amount of energy.
Applications
Though
metallic sodium has some important uses, the major applications of
sodium use it in its many compounds; millions of tons of the chloride,
hydroxide, and carbonate are produced annually.
Potassium
Potassium is a chemical element with symbol K (from Neo-Latin kalium)
and atomic number 19. Elemental potassium is a soft silvery-white alkali
metal that oxidizes rapidly in air and is very reactive with water,
generating sufficient heat to ignite the hydrogen emitted in the
reaction and burning with a lilac flame. Because potassium and sodium
are chemically very similar, their salts were not at first
differentiated. The existence of multiple elements in their salts was
suspected from 1702, and this was proven in 1807 when potassium and
sodium were individually isolated from different salts by electrolysis.
Potassium in nature occurs only in ionic salts. As such, it is found
dissolved in seawater (which is 0.04% potassium by weight), and is part
of many minerals.
Most industrial chemical applications of
potassium employ the relatively high solubility in water of potassium
compounds, such as potassium soaps. Potassium metal has only a few
special applications, being replaced in most chemical reactions with
sodium metal.
Properties
Physical
Potassium atoms
have 19 electrons, which is one more than the extremely stable
configuration of argon. A potassium atom is thus much more likely to
lose the "extra" electron than to gain one; however, the alkalide ions,
K–, are known. Because of the low first ionization energy (418.8 kJ/mol)
the potassium atom easily loses an electron and oxidizes into the
monopositive cation, K+. This process requires so little energy that
potassium
is readily oxidized by atmospheric oxygen. In contrast, the second
ionization energy is very high (3052 kJ/mol), because removal of two
electrons breaks the stable noble gas electronic configuration.
Potassium therefore does not readily form compounds with the oxidation
state of +2 (or higher). Potassium is the second least dense metal after
lithium. It is a soft solid that has a low melting point and can easily
be cut with a knife. Freshly cut potassium is silvery in appearance,
but it begins to tarnish toward gray immediately after being exposed to
air. In a flame test, potassium and its compounds emit a lilac color
with a peak emission wavelength of 766.5 nm (see movie below).
Chemical
Potassium
is an extremely active metal, which reacts violently with oxygen and
water in air. With oxygen, it converts to potassium peroxide and with
water potassium hydroxide. The reaction of potassium with water is
dangerous because of its violent exothermic character and the production
of hydrogen gas. Hydrogen reacts again with atmospheric oxygen,
producing water, which reacts with the remaining potassium. This
reaction requires only traces of water; because of this, potassium and
its liquid alloy with sodium — NaK — are potent desiccants that can be
used to dry solvents prior to distillation.
Because of the
sensitivity of potassium to water and air, the reactions are possible
only in inert atmosphere, such as argon gas using air-free techniques.
Potassium does not react with most hydrocarbons, such as mineral oil or
kerosene. It readily dissolves in liquid ammonia, up to 480 g per 1000 g
of ammonia at 0 °C. Depending on the concentration, the ammonia
solutions are blue to yellow, and their electrical conductivity is
similar to that of liquid metals. In a pure solution, potassium slowly
reacts with ammonia to form KNH2, but this reaction is accelerated by
minute amounts of transition metal salts. It can reduce the salts to the
metal; potassium is often used as the reductant in the preparation of
finely divided metals from their salts by the Rieke method. For example,
the preparation of Rieke magnesium employs potassium as the reductant:
MgCl2 + 2 K → Mg + 2 KCl
Applications
Fertilizer Potassium ions are an essential
component of plant nutrition and are found in most soil types. They are
used as a fertilizer in agriculture, horticulture, and hydroponic
culture in the form of chloride (KCl), sulfate (K2SO4) or nitrate
(KNO3). Agricultural fertilizers consume 95% of global potassium
chemical production, and about 90% of this potassium is supplied as KCl.
The potassium content of most plants range from 0.5% to 2% of the
harvested weight of crops, conventionally expressed as amount of K2O.
Modern high-yield agriculture depends upon fertilizers to replace the
potassium lost at harvest. Most agricultural fertilizers contain
potassium chloride, while potassium sulfate is used for
chloride-sensitive crops or crops needing higher sulfur content. The
sulfate is produced mostly by decomposition of the complex minerals
kainite (MgSO4·KCl·3H2O) and langbeinite (MgSO4·K2SO4). Only a very few
fertilizers contain potassium nitrate. In 2005, about 93% of world
potassium production was consumed by the fertilizer industry.
Food
The potassium cation is a nutrient necessary for human life and health.
Potassium chloride is used as a substitute for table salt by those
seeking to reduce sodium intake so as to control hypertension. The USDA
lists tomato paste, orange juice, beet greens, white beans, potatoes,
bananas and many other good dietary sources of potassium, ranked in
descending order according to potassium content. Potassium sodium
tartrate (KNaC4H4O6, Rochelle salt) is the main constituent of baking
powder; it is also used in the silvering of mirrors. Potassium bromate
(KBrO 3) is a strong oxidizer (E924), used to improve dough strength and
rise height. Potassium bisulfite (KHSO3) is used as a food
preservative, for example in wine and beer-making (but not in meats). It
is also used to bleach textiles and straw, and in the tanning of
leathers.
Industrial
Major potassium chemicals are
potassium hydroxide, potassium carbonate, potassium sulfate, and
potassium chloride. Megatons of these compounds are produced annually.
Potassium hydroxide KOH is a strong base, which is used in industry to
neutralize strong and weak acids, to control pH and to manufacture
potassium salts. It is also used to saponify fats and oils, in
industrial cleaners, and in hydrolysis reactions, for example of esters.
Potassium nitrate (KNO3) or saltpeter is obtained from natural sources
such as guano and evaporites or manufactured via the Haber process; it
is the oxidant in gunpowder (black powder) and an important agricultural
fertilizer. Potassium cyanide (KCN) is used industrially to dissolve
copper and precious metals, in particular silver and gold, by forming
complexes. Its applications include gold mining, electroplating, and
electroforming of these metals; it is also used in organic synthesis to
make nitriles. Potassium carbonate (K2CO3 or potash) is used in the
manufacture of glass, soap, color TV tubes, fluorescent lamps, textile
dyes and pigments.[83] Potassium permanganate (KMnO4) is an oxidizing,
bleaching and purification substance and is used for production of
saccharin. Potassium chlorate (KClO3) is added to matches and
explosives. Potassium bromide (KBr) was formerly used as a sedative and
in photography. Potassium chromate (K2CrO4) is used in inks, dyes,
stains (bright yellowish-red color); in explosives and fireworks; in the
tanning of leather, in fly paper and safety matches, but all these uses
are due to the properties of chromate ion containment rather than
potassium ions.
Niche uses
Potassium compounds are so
pervasive that thousands of small uses are in place. The superoxide KO2
is an orange solid that acts as a portable source of oxygen and a carbon
dioxide absorber. It is widely used in respiration systems in mines,
submarines and spacecraft as it takes less volume than the gaseous
oxygen.
4 KO2 + 2 CO2 → 2 K2CO3 + 3 O2 Potassium cobaltinitrite
K3[Co(NO2)6] is used as artist's pigment under the name of Aureolin or
Cobalt Yellow.
Laboratory uses An alloy of sodium and potassium,
NaK is a liquid used as a heat-transfer medium and a desiccant for
producing dry and air-free solvents. It can also be used in reactive
distillation. The ternary alloy of 12% Na, 47% K and 41% Cs has the
lowest melting point of −78 °C of any metallic compound.
Precautions Potassium reacts very violently with water producing potassium hydroxide (KOH) and hydrogen gas.
2 K (s) + 2 H2O (l) → 2 KOH (aq) + H2↑ (g)
This
reaction is exothermic and releases enough heat to ignite the resulting
hydrogen. It in turn may explode in the presence of oxygen. Potassium
hydroxide is a strong alkali that causes skin burns. Finely divided
potassium will ignite in air at room temperature. The bulk metal will
ignite in air if heated. Because its density is 0.89 g/cm3, burning
potassium floats in water that exposes it to atmospheric oxygen. Many
common fire extinguishing agents, including water, either are
ineffective or make a potassium fire worse. Nitrogen, argon, sodium
chloride (table salt), sodium carbonate (soda ash), and silicon dioxide
(sand) are effective if they are dry. Some Class D dry powder
extinguishers designed for metal fires are also effective. These agents
deprive the fire of oxygen and cool the potassium metal. Potassium
reacts violently with halogens and will detonate in the presence of
bromine. It also reacts explosively with sulfuric acid. During
combustion potassium forms peroxides and superoxides. These peroxides
may react violently with organic compounds such as oils. Both peroxides
and superoxides may react explosively with metallic potassium.
Because
potassium reacts with water vapor present in the air, it is usually
stored under anhydrous mineral oil or kerosene. Unlike lithium and
sodium, however, potassium should not be stored under oil for longer
than 6 months, unless in an inert (oxygen free) atmosphere, or under
vacuum. After prolonged storage in air dangerous shock-sensitive
peroxides can form on the metal and under the lid of the container, and
can detonate upon opening.
Because of the highly reactive nature
of potassium metal, it must be handled with great care, with full skin
and eye protection and preferably an explosion-resistant barrier between
the user and the metal. Ingestion of large amounts of potassium
compounds can lead to hyperkalemia strongly influencing the
cardiovascular system. Potassium chloride is used in the United States
for executions via lethal injection.
Aluminium
Aluminium (or aluminum) is a chemical element in the boron
group with symbol Al and atomic number 13. It is a silvery white, soft,
ductile metal. Aluminium is the third most abundant element (after
oxygen and silicon), and the most abundant metal, in the Earth's crust.
It makes up about 8% by weight of the Earth's solid surface. Aluminium
metal is so chemically reactive that native specimens are rare and
limited to extreme reducing environments. Instead, it is found combined
in over 270 different minerals. The chief ore of aluminium is bauxite.
Aluminium is remarkable for the metal's low density and for its ability
to resist corrosion due to the phenomenon of passivation. Structural
components made from aluminium and its alloys are vital to the aerospace
industry and are important in other areas of transportation and
structural materials. The most useful compounds of aluminium, at least
on a weight basis, are the oxides and sulfates.
Despite its
prevalence in the environment, aluminium salts are not known to be used
by any form of life. In keeping with its pervasiveness, aluminium is
well tolerated by plants and animals. Owing to their prevalence,
potential beneficial (or otherwise) biological roles of aluminium
compounds are of continuing interest.
Properties
Physical Aluminium is a relatively soft, durable, lightweight, ductile and
malleable metal with appearance ranging from silvery to dull gray,
depending on the surface roughness. It is nonmagnetic and does not
easily ignite. A fresh film of aluminium serves as a good reflector
(approximately 92%) of visible light and an excellent reflector (as much
as 98%) of medium and far infrared radiation. The yield strength of
pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths
ranging from 200 MPa to 600 MPa. Aluminium has about one-third the
density and stiffness of steel. It is easily machined, cast, drawn and
extruded. Aluminium atoms are arranged in a face-centered cubic (fcc)
structure. Aluminium has a stacking-fault energy of approximately 200
mJ/m2. Aluminium is a good thermal and electrical conductor, having 59%
the conductivity of copper, both thermal and electrical, while having
only 30% of copper's density. Aluminium is capable of being a
superconductor, with a superconducting critical temperature of 1.2
Kelvin and a critical magnetic field of about 100 gauss (10
milliteslas).
Chemical Corrosion resistance can be excellent due
to a thin surface layer of aluminium oxide that forms when the metal is
exposed to air, effectively preventing further oxidation. The strongest
aluminium alloys are less corrosion resistant due to galvanic reactions
with alloyed copper. This corrosion resistance is also often greatly
reduced by aqueous salts, particularly in the presence of dissimilar
metals.
Owing to its resistance to corrosion, aluminium is one of
the few metals that retain silvery reflectance in finely powdered form,
making it an important component of silver-colored paints. Aluminium
mirror finish has the highest reflectance of any metal in the 200–400 nm
(UV) and the 3,000–10,000 nm (far IR) regions; in the 400–700 nm
visible range it is slightly outperformed by tin and silver and in the
700–3000 (near IR) by silver, gold, and copper.
Aluminium is oxidized by water to produce hydrogen and heat:
2 Al + 3 H2O → Al2O3 + 3 H2
This
conversion is of interest for the production of hydrogen. Challenges
include circumventing the formed oxide layer which inhibits the reaction
and the expenses associated with the storage of energy by regeneration
of the Al metal.
Phosphorus
Phosphorus is a nonmetallic
chemical element with symbol P and atomic number 15. A multivalent
pnictogen, phosphorus as a mineral is almost always present in its
maximally oxidised state, as inorganic phosphate rocks. Elemental
phosphorus exists in two major forms—white phosphorus and red
phosphorus—but due to its high reactivity, phosphorus is never found as a
free element on Earth.
The first form of elemental phosphorus to
be produced (white phosphorus, in 1669) emits a faint glow upon
exposure to oxygen – hence its name given from Greek mythology, Φωσφόρος
meaning "light-bearer" (Latin Lucifer), referring to the "Morning
Star", the planet Venus. The term "phosphorescence", meaning glow after
illumination, originally derives from this property of phosphorus,
although this word has since been used for a different physical process
that produces a glow. The glow of phosphorus itself originates from
oxidation of the white (but not red) phosphorus— a process now termed
chemiluminescence. The vast majority of phosphorus compounds are
consumed as fertilisers. Other applications include the role of
organophosphorus compounds in detergents, pesticides and nerve agents,
and matches. Phosphorus is essential for life. As phosphate, it is a
component of DNA, RNA, ATP, and also the phospholipids that form all
cell membranes. Demonstrating the link between phosphorus and life,
elemental phosphorus was historically first isolated from human urine,
and bone ash was an important early phosphate source. Phosphate minerals
are fossils. Low phosphate levels are an important limit to growth in
some aquatic systems. The chief commercial use of phosphorus compounds
for production of fertilisers is due to the need to replace the
phosphorus that plants remove from the soil.
Iron
Iron is a chemical element with the symbol Fe (from Latin:
ferrum) and atomic number 26. It is a metal in the first transition
series. It is the most common element (by mass) forming the planet Earth
as a whole, forming much of Earth's outer and inner core. It is the
fourth most common element in the Earth's crust. Iron's very common
presence in rocky planets like Earth is due to its abundant production
as a result of fusion in high-mass stars, where the production of
nickel-56 (which decays to the most common isotope of iron) is the last
nuclear fusion reaction that is exothermic. This causes radioactive
nickel to become the last element to be produced before collapse of a
supernova leads to the explosive events that scatter this precursor
radionuclide of iron abundantly into space. Like other group 8 elements,
iron exists in a wide range of oxidation states, −2 to +6, although +2
and +3 are the most common. Elemental iron occurs in meteoroids and
other low oxygen environments, but is reactive to oxygen and water.
Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal
air to give hydrated iron oxides, commonly known as rust. Unlike many
other metals which form passivating oxide layers, iron oxides occupy
more volume than iron metal, and thus iron oxides flake off and expose
fresh surfaces for corrosion.
Calcium
Is the chemical element with symbol
Ca and atomic number 20. Calcium is a soft gray alkaline earth metal,
and is the fifth-most-abundant element by mass in the Earth's crust.
Calcium is also the fifth-most-abundant dissolved ion in seawater by
both molarity and mass, after sodium, chloride, magnesium, and sulfate.
Calcium is essential for living organisms, in particular in cell
physiology, where movement of the calcium ion Ca2+ into and out of the
cytoplasm functions as a signal for many cellular processes. As a major
material used in mineralization of bone, teeth and shells, calcium is
the most abundant metal by mass in manyanimals.
History
Lime
as building material was used since prehistoric times going as far back
as 7000 to 14000 BC. The first dated lime kiln dates back to 2500 BC
and was found in Khafajah mesopotamia. Calcium (from Latin calx,
genitive calcis, meaning "lime") was known as early as the first century
when the Ancient Romans prepared lime as calcium oxide. Literature
dating back to 975 AD notes that plaster of paris(calcium sulfate), is
useful for setting broken bones. It was not isolated until 1808 in
England when Sir Humphry Davy electrolyzed a mixture of lime and
mercuric oxide. Davy was trying to isolate calcium; when he heard that
Swedish chemist Jöns Jakob Berzelius and Pontin prepared calcium amalgam
by electrolyzing lime in mercury, he tried it himself. He worked with
electrolysis throughout his life and also discovered/isolated sodium,
potassium, magnesium, boron and barium. Calcium metal was not available
in large scale until the beginning of the 20th century.
Nickel
Nickel is a chemical element with the chemical symbol Ni and
atomic number 28. It is a silvery-white lustrous metal with a slight
golden tinge. Nickel belongs to the transition metals and is hard and
ductile. Pure nickel shows a significant chemical activity that can be
observed when nickel is powdered to maximize the exposed surface area on
which reactions can occur, but larger pieces of the metal are slow to
react with air at ambient conditions due to the formation of a
protective oxide surface. Even then, nickel is reactive enough with
oxygen so that native nickel is rarely found on Earth's surface, being
mostly confined to the interiors of larger nickel–iron meteorites that
were protected from oxidation during their time in space. On Earth, such
native nickel is always found in combination with iron, a reflection of
those elements' origin as major end products of supernova
nucleosynthesis. An iron–nickel mixture is thought to compose Earth's
inner core. The use of nickel (as a natural meteoric nickel–iron alloy)
has been traced as far back as 3500 BC. Nickel was first isolated and
classified as a chemical element in 1751 by Axel Fredrik Cronstedt, who
initially mistook its ore for a copper mineral. The element name comes
from a mischievous sprite of German miner's mythology, Nickel (similar
to Old Nick), that personified the fact that copper-nickel ores resisted
refinement into copper. An economically important source of nickel is
the iron ore limonite, which often contains 1-2% nickel. Nickel's other
important ore minerals include garnierite, and pentlandite. Major
production sites includeSudbury region in Canada (which is thought to be
of meteoric origin), New Caledonia in the Pacific and Norilsk in Russia
.
Manganese
Is a chemical element, designated by
the symbol Mn. It has the atomic number 25. It is found as a free
element in nature (often in combination with iron), and in many
minerals. Manganese is a metal with important industrial metal alloy
uses, particularly in stainless steels. Historically, manganese is named
for various black minerals (such as pyrolusite) from the same region of
Magnesia in Greece which gave names to similar-sounding magnesium, Mg,
and magnetite, an ore of the element iron, Fe. By the mid-18th century,
Swedish chemist Carl Wilhelm Scheelehad used pyrolusite to produce
chlorine. Scheele and others were aware that pyrolusite (now known to be
manganese dioxide) contained a new element, but they were not able to
isolate it. Johan Gottlieb Gahn was the first to isolate an impure
sample of manganese metal in 1774, byreducing the dioxide with carbon.
Manganese phosphating is used as a treatment for rust and corrosion
prevention on steel. Depending on their oxidation state, manganese ions
have various colors and are used industrially as pigments. The
permanganates of alkali and alkaline earth metals are powerful
oxidizers. Manganese dioxide is used as the cathode (electron acceptor)
material in zinc-carbon and alkaline batteries. In biology, manganese
(II) ions function as cofactors for a large variety of enzymes with many
functions. Manganese enzymes are particularly essential in
detoxification of superoxide free radicals in organisms that must deal
with elemental oxygen. Manganese also functions in the oxygen-evolving
complex of photosynthetic plants. The element is a required trace
mineral for all known living organisms. In larger amounts, and
apparently with far greater activity by inhalation, manganese can cause a
poisoning syndrome in mammals, with neurological damage which is
sometimes irreversible.
Beryllium
Beryllium is the chemical element with the symbol Be and
atomic number 4. Because any beryllium synthesized in stars is
short-lived, it is a relatively rare element in both the universe and in
the crust of the Earth. It is a divalent element which occurs naturally
only in combination with other elements in minerals. Notable gemstones
which contain beryllium include beryl (aquamarine, emerald) and
chrysoberyl. As a free element it is a steel-gray, strong, lightweight
and brittle alkaline earth metal.
Beryllium increases hardness
and resistance to corrosion when alloyed with aluminium, cobalt, copper
(notably beryllium copper), iron and nickel.[3] In structural
applications, high flexural rigidity, thermal stability, thermal
conductivity and low density (1.85 times that of water) make beryllium a
quality aerospace material for high-speed aircraft, missiles, space
vehicles and communication satellites. Because of its low density and
atomic mass, beryllium is relatively transparent to X-rays and other
forms of ionizing radiation; therefore, it is the most common window
material for X-ray equipment and in particle physics experiments. The
high thermal conductivities of beryllium and beryllium oxide have led to
their use in heat transport and heat sinking applications.
The
commercial use of beryllium presents technical challenges due to the
toxicity (especially by inhalation) of beryllium-containing dusts.
Beryllium is corrosive to tissue, and can cause a chronic
life-threatening allergic disease called berylliosis in some people. The
element is not known to be necessary or useful for either plant or
animal life.
Simply put formulation is the mixing of compounds
which do not react in order to get a mixture with the desired
characteristics. Examples of formulations are adhesives, paints, inks,
cosmetics, detergents and many pharmaceutical products. 
One specific
target for possible treatment with cellular therapies is Parkinson's
disease, which causes the death of nerve cells in the brain that are
needed for agile and controlled muscle movement. Symptoms of the
disabling malady include hand tremors and an inability to walk. Dr. Rao,
in collaboration with researchers at his previous position, developed
methods to induce stem cells to transform into the type of nerve cells
that are depleted in Parkinson's disease. These nerve cells produce
dopamine, a chemical signal that helps deliver the brain's orders to the
muscles. Their team was been able to derive such nerve cells from
embryonic stem cells, and also from the modified adult cells, called
induced pluripotent stem cells. These induced pluripotent stem cells can
mimic the versatility of embryonic stem cells. 
