Hydrogen: the essentials

Brief description: hydrogen is the lightest element. It is by far the most abundant element in the universe and makes up about 90% of the universe by weight. Hydrogen as water (H2O) is absolutely essential to life and it is present in all organic compounds. Hydrogen is the lightest gas. Hydrogen gas was used in lighter-than-air balloons for transport but is far too dangerous because of the fire risk (Hindenburg). It burns in air to form only water as waste product and if hydrogen could be made on sufficient scale from other than fossil fuels then there might be a possibility of a hydrogen economy.

Note that while normally shown at the top of the Group 1 elements in the periodic table, the term "alkaline metal" refers only to Group 1 elements from lithium onwards.

Table: basic information about and classifications of hydrogen. Name: Hydrogen Symbol: H Atomic number: 1 Atomic weight: 1.00794 (7) [see notes g m r] Standard state: gas at 298 K

CAS Registry ID: 1333-74-0

Group in periodic table: 1 Group name: (none) Period in periodic table: 1 Block in periodic table: s-block Color: colorless

Classification: Non-metallic

The lifting agent for the ill fated Hindenburg balloon was hydrogen rather than the safer helium.

Isolation

Isolation: in the laboratory, small amounts of hydrogen gas may be made by the reaction of calcium hydride with water.

CaH2 + 2H2O → Ca(OH)2 + 2H2

This is quite efficient in the sense that 50% of the hydrogen produced comes from water. Another very convenient laboratory scale experiment follows Boyle's early synthesis, the reaction of iron filings with dilute sulphuric acid.

Fe + H2SO4 → FeSO4 + H2

Helium: the essentials

Brief description: helium is one of the so-called noble gases. Helium gas is an unreactive, colorless, and odorless monoatomic gas. Helium is available in pressurized tanks. Helium is the second most abundant element in the universe after hydrogen. α particles are doubly ionized helium atoms, He2+.

Helium is used in lighter than air balloons and while heavier than hydrogen, is far safer since helium does not burn. Speaking after breathing an atmosphere rich in helium results in a squeaky voice (don't try it!).

Table: basic information about and classifications of helium. Name: Helium Symbol: He Atomic number: 2 Atomic weight: 4.002602 (2) [see notes g r] Standard state: gas at 298 K

CAS Registry ID: 7440-59-7

Group in periodic table: 18 Group name: Noble gas Period in periodic table: 1 Block in periodic table: p-block Color: colorless

Classification: Non-metallic

Emma's first birthday balloon is filled with helium and so rises in air.Isolation

Isolation: there is very little helium on earth as nearly all present during and immediately after the earth's formation has long since been lost as it is so light. Just about all the helium remaining on the planet is the result of radioactive decay. While there is some helium in the atmosphere, currently its isolation from that source by liquefaction and separation of air is not normally economic. This is because it is easier, and cheaper, to isolate the gas from certain natural gases. Concentrations of helium in natural gas in the USA are as high as 7% and other good sources include natural gas from some sources in Poland. It is isolable from these gases by liquefaction and separation of from the natural gas. This would not normally be carried out in the laboratory and helium is available commercially in cylinders under pressure.

Lithium: the essentials

Brief description: lithium is a Group 1 (IA) element containing just a single valence electron (1s22s1). Group 1 elements are called "alkali metals". Lithium is a solid only about half as dense as water and lithium metal is the least dense metal. A freshly cut chunk of lithium is silvery, but tarnishes in a minute or so in air to give a grey surface. Its chemistry is dominated by its tendency to lose an electron to form Li+. It is the first element within the second period.

Lithium is mixed (alloyed) with aluminum and magnesium for light-weight alloys, and is also used in batteries, some greases, some glasses, and in medicine.

Table: basic information about and classifications of lithium. Name: Lithium Symbol: Li Atomic number: 3 Atomic weight: [ 6.941 (2)] [see notes g m r] Standard state: solid at 298 K

CAS Registry ID: 7439-93-2

Group in periodic table: 1 Group name: Alkali metal Period in periodic table: 2 Block in periodic table: s-block Color: silvery white/grey

Classification: Metallic

Isolation

Isolation: lithium would not normally be made in the laboratory as it is so readily available commercially. All syntheses require an electrolytic step as it is so difficult to add an electron to the poorly electronegative lithium ion Li+.

The ore spodumene, LiAl(SiO3)2, is the most important commercial ore containing lithium. The α form is first converted into the softer β form by heating to around 1100°C. This is mixed carefully with hot sulphuric acid and extracted into water to form lithium sulphate, Li2SO4, solution. The sulphate is washed with sodium carbonate, Na2CO3, to form a precipitate of the relatively insoluble lithium carbonate, Li2CO3.

Li2SO4 + Na2CO3 → Na2SO4 + Li2CO3 (solid)

Reaction of lithium carbonate with HCl then provides lithium chloride, LiCl.

Li2CO3 + 2HCl → 2LiCl + CO2 +H2O

Lithium chloride has a high melting point (> 600°C) meaning that it should be expensive to melt it in order to carry out the electrolysis. However a mixture of LiCl (55%) and KCl (45%) melts at about 430°C and so much less energy and so expense is required for the electrolysis.

cathode: Li+(l) + e- → Li (l)anode: Cl-(l) → 1/2Cl2 (g) + e-

Beryllium: the essentials

Brief description: beryllium is a Group 2 (IIA) element. It is a metal and has a high melting point. At ordinary temperatures, beryllium resists oxidation in air. Beryllium compounds are very toxic. Its ability to scratch glass is probably due to the formation of a thin layer of the oxide. Aquamarine and emerald are precious forms of the mineral beryl, [Be3Al2(SiO3)6].

Its chemistry is dominated by its tendency to lose an electron to form Be2+. As this ion is so small it is highly polarizing, to the extent that its compounds are rather covalent. Its small size means that its complexes tend to be tetrahedral rather than octahedral.

Table: basic information about and classifications of beryllium. Name: Beryllium Symbol: Be Atomic number: 4 Atomic weight: 9.012182 (3) Standard state: solid at 298 K

CAS Registry ID: 7440-41-7

Group in periodic table: 2 Group name: Alkaline earth metal Period in periodic table: 2 Block in periodic table: s-block Color: lead grey

Classification: Metallic

Isolation

Isolation: beryllium metal is available commercially and so would never normally be made in the laboratory. Its extraction from ores is complex. The mineral beryl, [Be3Al2(SiO3)6] is the most important source of beryllium. It is roasted with sodium hexafluorosilicate, Na2SiF6, at 700°C to form beryllium fluoride. This is water soluble and the beryllium may be precipitated as the hydroxide Be(OH)2 by adjustment of the pH to 12.

Pure beryllium may be obtained by electrolysis of molten BeCl2 containing some NaCl. The salt is added since the molten BeCl2 conducts very poorly. Another method involves the reduction of beryllium fluoride with magnesium at 1300°C.

BeF2 + Mg → MgF2 + Be

Boron: the essentials

Brief description: boron is a Group 13 element that has properties which are borderline between metals and non-metals (semimetallic). It is a semiconductor rather than a metallic conductor. Chemically it is closer to silicon than to aluminum, gallium, indium, and thallium.

Crystalline boron is inert chemically and is resistant to attack by boiling HF or HCl. When finely divided it is attacked slowly by hot concentrated nitric acid.

Table: basic information about and classifications of boron. Name: Boron Symbol: B Atomic number: 5 Atomic weight: 10.811 (7) [see notes g m r] Standard state: solid at 298 K

CAS Registry ID: 7440-42-8

Group in periodic table: 13 Group name: (none) Period in periodic table: 2 Block in periodic table: p-block Color: black

Classification: Semi-metallic

Isolation

Isolation: it is not normally necessary to make boron in the laboratory and it would normally be purchased as it is available commercially. The most common sources of boron are tourmaline, borax [Na2B4O5(OH)4.8H2O], and kernite [Na2B4O5(OH)4.2H2O]. It is difficult to obtain pure. It can be made through the magnesium reduction of the oxide, B2O3. The oxide is made by melting boric acid, B(OH)3, which in turn is obtained from borax.

B2O3 + 3Mg → 2B + 3MgO

Some amounts of high purity boron are available through the thermal decomposition of compounds such as BBr3 with hydrogen gas using a heated tantalum wire. Results are better with hot wires at temperatures over 1000°C.

Carbon: the essentials

Brief description: carbon is a Group 14 element and is distributed very widely in nature. It is found in abundance in the sun, stars, comets, and atmospheres of most planets.

Carbon is found free in nature in three allotropic forms: amorphous, graphite, and diamond (further details). Graphite is one of the softest known materials while diamond is one of the hardest. Carbon, as microscopic diamonds, is found in some meteorites. Natural diamonds are found in ancient volcanic "pipes" such as found in South Africa. Diamonds are also recovered from the ocean floor off the Cape of Good Hope.

Table: basic information about and classifications of carbon. Name: Carbon Symbol: C Atomic number: 6 Atomic weight: 12.0107 (8) [see notes g r] Standard state: solid at 298 K

CAS Registry ID: 7440-44-0

Group in periodic table: 14 Group name: (none) Period in periodic table: 2 Block in periodic table: p-block Color: graphite is black, diamond is colorless

Classification: Non-metallic

More recently, another form of carbon, buckminsterfullerene, C60, has been discovered. This new form of carbon is the subject of great interest in research laboratories today.

Carbon is present as carbon dioxide in the atmosphere and dissolved in all natural waters. It is a component of rocks as carbonates of calcium (limestone), magnesium, and iron. The atmosphere of Mars contains 96 % CO2.

Coal, petroleum, and natural gas are chiefly hydrocarbons. Carbon is unique among the elements in the vast number of variety of compounds it can form. Organic chemistry, a 1/112th subset of inorganic chemistry, is the study of carbon and its compounds. While silicon might take the place of carbon in forming a host of related compounds, it is not possible currently to form stable compounds with very long chains of silicon atoms.

In 1961 the International Union of Pure and Applied Chemistry (IUPAC) adopted the isotope 12C as the basis for atomic weights. Carbon-14, 14C, an isotope with a half-life of 5730 years, is used to date such materials as wood, archeological specimens, etc. Carbon-13, 13C, is particularly useful for isotopic labeling studies since it is not radioactive, but is a spin I = 1/2 nucleus and therefore a good NMR nucleus.

Isolation

Isolation: carbon is available in nature as graphite and (to a much lesser extent!) as diamond. Artificial graphite is made by the reaction of coke with silica (SiO2).

SiO2 + 3C (2500°C) → "SiC" → Si (g) + C(graphite)

Artificial diamonds are made by the application of heat and pressure (> 125 kBar) in the presence of a catalyst such as iron, chromium or platinum. It seems that the metal melts on the carbon surface, the graphite dissolves in the metal film, and the less soluble diamond precipitates out. The introduction of nitrogen as an impurity gives yellowish diamonds while boron impurities give bluish colors

A new form of carbon, buckminsterfullerene with formula C60 is formed in the treatment of graphite by lasers and is now commercially available in small quantities.

Nitrogen: the essentials

Brief description: nitrogen is a Group 15 element. Nitrogen makes up about 78% of the atmosphere by volume but the atmosphere of Mars contains less than 3% nitrogen. The element seemed so inert that Lavoisier named it azote, meaning "without life". However, its compounds are vital components of foods, fertilizers, and explosives. Nitrogen gas is colorless, odorless, and generally inert. As a liquid it is also colorless and odorless.

When nitrogen is heated, it combines directly with magnesium, lithium, or calcium. When mixed with oxygen and subjected to electric sparks, it forms nitric oxide (NO) and then the dioxide (NO2). When heated under pressure with hydrogen in the presence of a suitable catalyst , ammonia forms (Haber process). Nitrogen is "fixed" from the atmosphere by bacteria in the roots of certain plants such as clover. Hence the usefulness of clover in crop rotation.

Table: basic information about and classifications of nitrogen. Name: Nitrogen Symbol: N Atomic number: 7 Atomic weight: 14.0067 (2) [see notes g r] Standard state: gas at 298 K

CAS Registry ID: 7727-37-9

Group in periodic table: 15 Group name: Pnictogen Period in periodic table: 2 Block in periodic table: p-block Color: colorless

Classification: Non-metallic

The result of touching nitrogen triiodide (NI3)! Nitrogen triiodide is dangerously percussion sensitive (only to be demonstrated by a professionally qualified chemist following a legally satisfactory hazard assessment). Improperly done, this reaction is dangerous!

Isolation

Isolation: there is never any need to make nitrogen in the laboratory as it is readily available commercially or through in-house air liquefaction plants. However the decomposition of sodium azide is one route to N2 and decomposition is ammonium dichromate is another. Both reactions must only be carried out under controlled conditions by a professional.

NaN3 (300°C) → 2Na + 3N2

(NH4)2Cr2O7 → N2 + Cr2O3 + 4H2O

Nitrogen is made on massive scale by liquefaction of air and fractional distillation of the resulting liquid air to separate out oxygen and other gases. Very high purity nitrogen is available by this route.

Oxygen: the essentials

Brief description: oxygen is a Group 16 element. While about one fifth of the atmosphere is oxygen gas, the atmosphere of Mars contains only about 0.15% oxygen. Oxygen is the third most abundant element found in the sun, and it plays a part in the carbon-nitrogen cycle, one process responsible for stellar energy production. Oxygen in excited states is responsible for the bright red and yellow-green colors of the aurora. About two thirds of the human body, and nine tenths of water, is oxygen. The gas is colorless, odorless, and tasteless. Liquid and solid oxygen are pale blue (see picture above) and strongly paramagnetic (contains unpaired electrons).

Table: basic information about and classifications of oxygen. Name: Oxygen Symbol: O Atomic number: 8 Atomic weight: 15.9994 (3) [see notes g r] Standard state: gas at 298 K

CAS Registry ID: 7782-44-7

Group in periodic table: 16 Group name: Chalcogen Period in periodic table: 2 Block in periodic table: p-block Color: colorless as a gas, liquid is pale blue

Classification: Non-metallic

Ozone (O3) is another allotrope of oxygen. It is formed from electrical discharges or ultraviolet light acting on O2. It is an important component of the atmosphere (in total amounting to the equivalent of a layer about 3 mm thick at ordinary pressures and temperatures) which is vital in preventing harmful ultraviolet rays of the sun from reaching the earth's surface. Aerosols in the atmosphere have a detrimental effect on the ozone layer. Large holes in the ozone layer are forming over the polar regions and these are increasing in size annually. Paradoxically, ozone is toxic! Undiluted ozone is bluish in color. Liquid ozone is bluish-black, and solid ozone is violet-black.

Oxygen is very reactive and oxides of most elements are known. It is essential for respiration of all plants and animals and for most types of combustion.

Isolation

Isolation: there is not normally any need to make oxygen in the laboratory as it is readily available commercially or through in-house air liquefaction plants. However the decomposition of potassium chlorate is one route to O2 and decomposition of potassium permanganate is another. In addition, electrolysis of KOH using nickel electrodes gives clean oxygen.

2KClO3 (400°C) → 2KCl + 3O2

2KMnO4 (214°C) → K2MnO4 + MnO2 + O2

Ozone (O3), the other allotrope of oxygen, is made by silent electric discharge through oxygen flowing through a cooled system. This can give up to a10% proportion of ozone and the ozone is purified by fractional liquefaction (with care!).

Fluorine: the essentials

Brief description: fluorine is a Group 17 element. Fluorine is the most electronegative and reactive of all elements. It is a pale yellow, corrosive gas, which reacts with practically all organic and inorganic substances. Finely divided metals, glass, ceramics, carbon, and even water burn in fluorine with a bright flame. It is not uncommon to see fluorine spelled incorrectly as fluorine.

Table: basic information about and classifications of fluorine. Name: Fluorine Symbol: F Atomic number: 9 Atomic weight: 18.9984032 (5) Standard state: gas at 298 K

CAS Registry ID: 7782-41-4

Group in periodic table: 17 Group name: Halogen Period in periodic table: 2 Block in periodic table: p-block Color: pale yellow

Classification: Non-metallic

Until World War 2, there was no commercial production of elemental fluorine. Atom bomb projects and nuclear energy applications made it necessary to produce large quantities of fluorine since isotopes of uranium can be separated through the gas diffusion of UF6. Reasonably safe handling techniques for fluorine are now available and one can transport liquid fluorine by the ton. Compounds of fluorine with noble gases such as xenon, radon, and krypton are known. Elemental fluorine and the fluoride ion (in quantity) are highly toxic.

Isolation

Isolation: it would never be necessary to make fluorine gas in most laboratories. Fluorine is available commercially in cylinders but is very difficult to handle. Fluorine may be recovered with difficulty as a highly reactive and corrosive pale yellow gas by electrolysis of hot molten mixtures (1:2) of potassium fluoride (KF) and hydrogen fluoride (HF). The electrolyte is corrosive, so is the product. Grease must be avoided because of the fire hazard. It is difficult to store as it reacts with most materials but steel and metal containers may be used as the metal surfaces deactivate through the formation of unreactive surface fluorides.

Neon: the essentials

 Brief description: neon is a very inert element. Neon forms an unstable hydrate. In a vacuum discharge tube, neon glows reddish orange. Of all the rare gases, the discharge of neon is the most intense at ordinary voltages and currents. It is present in the atmosphere as 1 part in 65000. Liquid neon has over 40 times more refrigerating capacity than liquid helium, and more than 3 times that of liquid hydrogen.

Table: basic information about and classifications of neon. Name: Neon Symbol: Ne Atomic number: 10 Atomic weight: 20.1797 (6) [see notes g m] Standard state: gas at 298 K

CAS Registry ID: 7440-01-9

Group in periodic table: 18 Group name: Noble gas Period in periodic table: 2 Block in periodic table: p-block Color: colorless

Classification: Non-metallic

Isolation

Isolation: neon is present to a small extent in the atmosphere and is obtained as a byproduct from the liquefaction and separation of air. This would not normally be carried out in the laboratory and neon is available commercially in cylinders under pressure.

Sodium: the essentials

Brief description: sodium is a Group 1 element (or IA in older labeling styles). Group 1 elements are often referred to as the "alkali metals". The chemistry of sodium is dominated by the +1 ion Na+. Sodium salts impart a characteristic orange/yellow color to flames and orange street lighting is orange because of the presence of sodium in the lamp.

Soap is generally a sodium salt of fatty acids. The importance of common salt to animal nutrition has been recognized since prehistoric times. The most common compound is sodium chloride, (table salt).

Table: basic information about and classifications of sodium. Name: Sodium Symbol: Na Atomic number: 11 Atomic weight: 22.98976928 (2) Standard state: solid at 298 K

CAS Registry ID: 7440-23-5

Group in periodic table: 1 Group name: Alkali metal Period in periodic table: 3 Block in periodic table: s-block Color: silvery white

Classification: Metallic

Isolation

Isolation: sodium would not normally be made in the laboratory as it is so readily available commercially. All syntheses require an electrolytic step as it is so difficult to add an electron to the poorly electronegative sodium ion Na+.

Sodium is present as salt (sodium chloride, NaCl) in huge quantities in underground deposits (salt mines) and seawater and other natural waters. It is easily recovered as a solid by drying.

Sodium chloride has a high melting point (> 800°C) meaning that it should be expensive to melt it in order to carry out the electrolysis. However a mixture of NaCl (40%) and calcium chloride, CaCl2 (60%) melts at about 580°C and so much less energy and so expense is required for the electrolysis.

cathode: Na+(l) + e- → Na (l)anode: Cl-(l) → 1/2Cl2 (g) + e-

The electrolysis is carried out as a melt in a "Downs cell". In practice, the electrolysis process produces calcium metal as well but this is solidified in a collection pipe and returned back to the melt.

Magnesium: the essentials

Brief description: magnesium is a grayish-white, fairly tough metal. Magnesium is the eighth most abundant element in the earth's crust although not found in it's elemental form. It is a Group 2 element (Group IIA in older labeling schemes). Group 2 elements are called alkaline earth metals. Magnesium metal burns with a very bright light.

Magnesium is an important element for plant and animal life. Chlorophylls are porphyrins based upon magnesium. The adult human daily requirement of magnesium is about 0.3 g day-1.

Table: basic information about and classifications of magnesium. Name: Magnesium Symbol: Mg Atomic number: 12 Atomic weight: 24.3050 (6) Standard state: solid at 298 K

CAS Registry ID: 7439-95-4

Group in periodic table: 2 Group name: Alkaline earth metal Period in periodic table: 3 Block in periodic table: s-block Color: silvery white

Classification: Metallic

Magnesium tarnishes slightly in air, and finely divided magnesium readily ignites upon heating in air and burns with a dazzling white flame. Normally magnesium is coated with a layer of oxide, MgO, that protects magnesium from air and water.The result of aqueous ignition of a mixture of magnesium metal with silver nitrate with water (only to be demonstrated by a professionally qualified chemist following a legally satisfactory hazard assessment). Improperly done, this reaction is dangerous!

Isolation

Isolation: magnesium can be made commercially by several processes and would not normally be made in the laboratory because of its ready availability. There are massive amounts of magnesium in seawater. This can be recovered as magnesium chloride, MgCl2 through reaction with calcium oxide, CaO.

CaO + H2O → Ca2+ + 2OH-

Mg2+ + 2OH- → Mg(OH)2

Mg(OH)2 + 2HCl → MgCl2 + 2H2O

Electrolysis of hot molten MgCl2 affords magnesium as a liquid which is poured off and chlorine gas.

cathode: Mg2+(l) + 2e- → Mganode: Cl-(l) → 1/2Cl2 (g) + e-

The other methods used to produce magnesium is non electrolytic and involves dolomite, [MgCa(CO3)2], an important magnesium mineral. This is "calcined" by heating to form calcined dolomite, MgO.CaO, and this reacted with ferrosilicon alloy.

2[MgO.CaO] + FeSi → 2Mg + Ca2SiO4 + Fe

The magnesium may be distilled out from this mixture of products.

Aluminum: the essentials

Brief description: pure aluminum is a silvery-white metal with many desirable characteristics. It is light, nontoxic (as the metal), nonmagnetic and nonsparking. It is somewhat decorative. It is easily formed, machined, and cast. Pure aluminum is soft and lacks strength, but alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties. Aluminum is an abundant element in the earth's crust, but it is not found free in nature. The Bayer process is used to refine aluminum from bauxite, an aluminum ore.

Table: basic information about and classifications of aluminum. Name: Aluminum Symbol: Al Atomic number: 13 Atomic weight: 26.9815386 (8) Standard state: solid at 298 K

CAS Registry ID: 7429-90-5

Group in periodic table: 13 Group name: (none) Period in periodic table: 3 Block in periodic table: p-block Color: silvery

Classification: Metallic

Isolation

Isolation: aluminum would not normally be made in the laboratory as it is so readily available commercially.

Aluminum is mined in huge scales as bauxite (typically Al2O3.2H2O). Bauxite contains Fe2O3, SiO2, and other impurities. In order to isolate pure aluminum, these impurities must be removed from the bauxite. This is done by the Bayer process. This involves treatment with sodium hydroxide (NaOH) solution, which results in a solution of sodium aluminate and sodium silicate. The iron remains behind as a solid. When CO2 is blown through the resulting solution, the sodium silicate stays in solution while the aluminum is precipitated out as aluminum hydroxide. The hydroxide can be filtered off, washed, and heated to form pure alumina, Al2O3.

The next stage is formation of pure aluminum. This is obtained from the pure Al2O3 by an electrolytic method. Electrolysis is necessary as aluminum is so electropositive. It seems these days that electrolysis of the hot oxide in a carbon lined steel cell acting as the cathode with carbon anodes is most common.

Silicon: the essentials

Brief description: silicon is present in the sun and stars and is a principal component of a class of meteorites known as aerolites. Silicon makes up 25.7% of the earth's crust by weight, and is the second most abundant element, exceeded only by oxygen. It is found largely as silicon oxides such as sand (silica), quartz, rock crystal, amethyst, agate, flint, jasper and opal. Silicon is found also in minerals such as asbestos, feldspar, clay and mica.

Silicon is important in plant and animal life. Diatoms in both fresh and salt water extract silica from the water to use as a component of their cell walls. Silicon is an important ingredient in steel. Silicon carbide is one of the most important abrasives. Workers in environments where silicaceous dust is breathed may develop a serious lung disease known as silicosis.

Table: basic information about and classifications of silicon. Name: Silicon Symbol: Si Atomic number: 14 Atomic weight: 28.0855 (3) [see note r] Standard state: solid at 298 K

CAS Registry ID: 7440-21-3

Group in periodic table: 14 Group name: (none) Period in periodic table: 3 Block in periodic table: p-block Color: dark grey with a bluish tinge

Classification: Semi-metallic

Hydrolysis and condensation of substituted chlorosilanes can be used to produce a very great number of polymeric products, or silicones. These range from liquids to hard, glasslike solids with many useful properties.

Elemental silicon transmits more than 95% of all wavelengths of infrared and has been used in lasers to produce coherent light at 456 nm.

Isolation

Isolation: there is normally no need to make silicon in the laboratory as it is readily available commercially. Silicon is readily available through the treatment of silica, SiO2, with pure graphite (as coke) in an electric furnace.

SiO2 + 2C → Si + 2CO

Under these conditions, silicon carbide, SiC, can form. However, provided the amount of SiO2 is kept high, silicon carbide may be eliminated.

2SiC + SiO2 → 3Si + 2CO

Very pure silicon can be made by the reaction of SiCl4 with hydrogen, followed by zone refining of the resultant silicon.

SiCl4 + 2H2 → Si + 4HCl

Phosphorus: the essentials

Brief description: phosphorus is commonly misspelled "phosphorous". It is an essential component of living systems and is found in nervous tissue, bones and cell protoplasm. Phosphorus exists in several allotropic forms including white (or yellow), red, and black (or violet). White phosphorus has two modifications. Ordinary phosphorus is a waxy white solid. When pure, it is colorless and transparent. It is insoluble in water, but soluble in carbon disulphide. It catches fire spontaneously in air, burning to P4O10, often misnamed as phosphorus pentoxide. When exposed to sunlight, or when heated in its own vapor to 250°C, it is converted to the red variety. This form does not ignite spontaneously and it is a little less dangerous than white phosphorus. The red modification is fairly stable and sublimes with a vapor pressure of 1 atmosphere at 417°C.

Table: basic information about and classifications of phosphorus. Name: Phosphorus Symbol: P Atomic number: 15 Atomic weight: 30.973762 (2) Standard state: solid at 298 K

CAS Registry ID: 7723-14-0

Group in periodic table: 15 Group name: Pnictogen Period in periodic table: 3 Block in periodic table: p-block Color: colorless/red/silvery white

Classification: Non-metallic

Isolation

Isolation: originally, phosphorus was extracted from urine. However there is plenty of phosphorus in phosphate ores and those ores represent the usual source for commercially produced phosphorus. There is normally no need to make phosphorus in the laboratory as it is readily available commercially.

The usual route involves heating a phosphate with sand and carbon in an electric furnace. It is highly energy intensive.

2Ca3(PO4)2 + 6SiO2 + 10C (1500°C) → 6CaSiO3 + 10CO + P4

The reaction may proceed via "phosphorus pentoxide", P4O10.

2Ca3(PO4)2 + 6SiO2 + → 6CaSiO3 + P4O10

P4O10 + 10C → 10CO + P4

Sulfur: the essentials

Brief description: the spelling of sulphur is "sulfur" in the USA and now that IUPAC has decided it has jurisdiction over the British English language (as distinct from American English) as well as nomenclature, so we in the UK are expected to use the f word.

Sulphur is found in meteorites, volcanoes, hot springs, and as galena, gypsum, Epsom salts, and barite. It is recovered commercially from "salt domes" along the Gulf Coast of the USA.

Jupiter's moon Io owes its colors to various forms of sulphur. A dark area near the crater Aristarchus on the moon may be a sulphur deposit.

Sulphur is a pale yellow, odorless, brittle solid, which is insoluble in water but soluble in carbon disulphide. Sulphur is essential to life. It is a minor constituent of fats, body fluids, and skeletal minerals.

Carbon disulphide, hydrogen sulphide, and sulphur dioxide should be handled extremely carefully. Hydrogen sulphide in very small concentrations can be metabolized, but in higher concentrations it can cause death quickly by respiratory paralysis. It is insidious in that it quickly deadens the sense of smell. Sulphur dioxide is a dangerous component in atmospheric air pollution and is one of the factors responsible for acid rain.

Table: basic information about and classifications of sulfur. Name: Sulfur Symbol: S Atomic number: 16 Atomic weight: 32.065 (5) [see notes g r] Standard state: solid at 298 K

CAS Registry ID: 7704-34-9

Group in periodic table: 16 Group name: Chalcogen Period in periodic table: 3 Block in periodic table: p-block Color: lemon yellow

Classification: Non-metallic

Isolation

Isolation: it is not normally necessary to make sulphur in the laboratory as it is so readily available. It is found as the native element in nature and extracted by the Frasch process. This is an interesting process since it means that sulphur can be extracted from underground without mining it. In the Frasch process underground deposits of sulphur are forced to the surface using superheated water and steam (160°C, 16 atmospheres, to melt the sulphur) and compressed air (25 atmospheres). This gives molten sulphur which is allowed to cool in large basins. Purity can reach 99.5%.

The process in energy intensive. Commercial success for this operation depends upon suitable geological conditions as well as access to cheap water and energy.

Hydrogen sulphide, H2S, is an important impurity in natural gas which must be removed before the gas is used. This is done by an absorption and regeneration process to concentrate the H2S, followed by a catalytic oxidation (Claus process) using porous catalysts such as Al2O3 or Fe2O3.

8H2S + 4O2 → S8 + 8H2O

Over the years the Claus process has been improved and a modified process can yield 98% recovery.

In the laboratory, sulphur can be purified by recrystalization from solutions in carbon disulphide, CS2. However the resulting crystals are contaminated with solvent, H2S, and SO2. One good way to purify sulphur is to use a quartz heater (700°C) immersed in liquid sulphur. Carbon impurities decompose to form volatile materials of solid carbon, which coat the heater. After a week or so, finishing with a distillation under vacuum, the result is sulphur with a carbon content of about 0.0009%.

Chlorine: the essentials

Brief description: chlorine is a greenish yellow gas which combines directly with nearly all elements. Chlorine is a respiratory irritant. The gas irritates the mucous membranes and the liquid burns the skin. As little as 3.5 ppm can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths. It was used as a war gas in 1915. It is not found in a free state in nature, but is found commonly as NaCl (solid or seawater).

Table: basic information about and classifications of chlorine. Name: Chlorine Symbol: Cl Atomic number: 17 Atomic weight: 35.453 (2) [see notes g m] Standard state: gas at 298 K

CAS Registry ID: 7782-50-5

Group in periodic table: 17 Group name: Halogen Period in periodic table: 3 Block in periodic table: p-block Color: yellowish green

Classification: Non-metallic

Isolation

Isolation: it is rarely necessary to make chlorine in the laboratory as it is readily available commercially in cylinders. Chlorine is found largely in seawater where it exists as sodium chloride. It is recovered as a reactive, corrosive, pale green chlorine gas from brine (a solution of sodium chloride in water) by electrolysis. Electrolysis of molten salt, NaCl, also succeeds, in which case the other product is sodium metal rather than sodium hydroxide.

Na+ + Cl- + H2O → Na+ + 1/2Cl2 + 1/2H2 + OH-

In the laboratory under carefully controlled conditions, chlorine can be made by the action of an oxidizing agent such as manganese dioxide, MnO2, upon concentrated hydrochloric acid - the same reaction used by Scheele in 1774 when discovering chlorine.

MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O

Argon: the essentials

Brief description: argon is a colorless and odorless gas present to a very small extent in the atmosphere. Argon is very inert (indeed it is referred to as one of the noble gases) and is not known to form true chemical compounds. It makes a good atmosphere for working with air-sensitive materials since it is heavier than air and less reactive than N2. Today, the chemical symbol for argon is Ar but until 1957 its symbol was simply A.

Table: basic information about and classifications of argon. Name: Argon Symbol: Ar Atomic number: 18 Atomic weight: 39.948 (1) [see notes g r] Standard state: gas at 298 K

CAS Registry ID: 7440-37-1

Group in periodic table: 18 Group name: Noble gas Period in periodic table: 3 Block in periodic table: p-block Color: colorless

Classification: Non-metallic

Isolation

Isolation: argon is present to a small extent in the atmosphere and is obtained as a byproduct from the liquefaction and separation of air. This would not normally be carried out in the laboratory and argon is available commercially in cylinders at high pressure.

Potassium: the essentials

Brief description: potassium is a metal and is the seventh most abundant and makes up about 1.5 % by weight of the earth's crust. Potassium is an essential constituent for plant growth and it is found in most soils. It is also a vital element in the human diet.Potassium is never found free in nature, but is obtained by electrolysis of the chloride or hydroxide, much in the same manner as prepared by Davy. It is one of the most reactive and electropositive of metals and, apart from lithium, it is the least dense known metal. It is soft and easily cut with a knife. It is silvery in appearance immediately after a fresh surface is exposed.It oxidises very rapidly in air and must be stored under argon or under a suitable mineral oil. As do all the other metals of the alkali group, it decomposes in water with the evolution of hydrogen. It usually catches fire during the reaction with water. Potassium and its salts impart a lilac colour to flames.

Table: basic information about and classifications of potassium. Name: Potassium Symbol: K Atomic number: 19 Atomic weight: 39.0983 (1) Standard state: solid at 298 K

CAS Registry ID: 7440-09-7

Group in periodic table: 1 Group name: Alkali metal Period in periodic table: 4 Block in periodic table: s-block Colour: silvery white

Classification: Metallic

The following uses for potassium are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses (please use the feedback mechanism to add uses).

The superoxide KO2 is used in breathing apparatus where moisture in the breath and carbon dioxide reacts with it to release oxygen [2KO2 + H2O + 2CO2 → 2KHCO3 + O2 ]

the alloy of potassium with sodium (NaK) is used as a heat-transfer medium in nuclear reactors. The alloy is liquid at ambient temperature and is a good reducing agent in the chemistry laboratory

fertilizers - usually as the chloride, sulphate, nitrate, or carbonate possium nitrate, KNO3, and potassium chlorate, KClO3, are used in fireworks potassium bromide, KBr, was used as an antaphrodisiac - oh dear! potassium permanganate, KMnO4, is an important oxidizing agent low-sodium salt potassium hydroxide is used in the preparation of potassium phosphates for liquid detergents

Calcium: the essentials

Brief description: calcium as the element is a grey silvery metal. The metal is rather hard. Calcium is an essential constituent of leaves, bones, teeth, and shells. Calcium is the fifth most abundant element in the earth's crust and makes up more than 3% of the crust. Calcium does not occur as the metal itself in nature and instead is found in various minerals including as limestone, gypsum and fluorite. Stalagmites and stalactites contain calcium carbonate (CaCO3). Calcium carbonate is the basis of the cement industry.Calcium is classified chemically as one of the alkaline earth elements (that is, in Group 2 of the periodic table. The metal is rather reactive. It readily forms a white coating of calcium nitride (Ca3N2) in air. It reacts with water and the metal burns with a yellow-red flame, forming largely the nitride.Table: basic information about and classifications of calcium.

Name: Calcium Symbol: Ca Atomic number: 20 Atomic weight: 40.078 (4) [see note g] Standard state: solid at 298 K

CAS Registry ID: 7440-70-2

Group in periodic table: 2 Group name: Alkaline earth metal Period in periodic table: 4 Block in periodic table: s-block Colour: silvery white

Classification: Metallic

The following uses for calcium are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses (please use the feedback mechanism to add uses).

reducing agent for the preparation of metals such as thorium, uranium, zirconium, etc.

deoxidiser, desulphurizer, or decarbonizer for various alloys

alloys of calcium with agent for aluminium, beryllium, copper, lead, and magnesium have some useful properties

"getter" for residual gases in vacuum tubes, etc.

quicklime (CaO) is made by heating limestone (CaCO3) and changes into slaked lime, Ca(OH)2, on the addition of water. It is a cheap base for the chemical industry with many uses.

calcium from limestone is a component of Portland cement. Mixed with sand it hardens as mortar and plaster while taking up carbon dioxide from the air

the solubility of the carbonate in water containing carbon dioxide results in stalactites and stalagmites (Cheddar Gorge) and hardness in water.