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 gmr]
  • Standard state: gas at 298 K
  • CAS Registry ID: 1333-74-0
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  • 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 Hindenburgballoon 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 gr]
  • 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 gmr]
  • 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
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  • 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 gmr]
  • 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 gr]
  • Standard state: solid at 298 K
  • CAS Registry ID: 7440-44-0
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  • 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 gr]
  • 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 gr]
  • Standard state: gas at 298 K
  • CAS Registry ID: 7782-44-7
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  • 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.