carbon group elementany of the five chemical elements that make up Group IVa Via of the periodic table—namely, carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). (See Figure.)



Carbon as an element was discovered by the first man to handle charcoal from his fire; thus, together with sulfur, iron, tin, lead, copper, mercury, silver, and gold, carbon was one of the small group of elements well known in the ancient world. Modern carbon chemistry dates from the development of coals, petroleum, and natural gas as fuels and from the elucidation of synthetic organic chemistry, both substantially developed since the 1800s.

Amorphous elemental silicon was first obtained in a state of purity in 1824 by the Swedish chemist Jöns Jacob Berzelius; impure silicon had already been obtained in 1811. Crystalline elemental silicon was not prepared until 1854, when it was obtained as a product of electrolysis. In the form of rock crystal, however, silicon was familiar to the predynastic Egyptians, who used it for beads and small vases; to the early Chinese; and probably to many others of the ancients. The manufacture of glass containing silica was carried out both by the Egyptians—at least as early as 1500 BC—and by the Phoenicians. Certainly, many of the naturally occurring compounds called silicates were used in various kinds of mortar for construction of dwellings by the earliest people.

Germanium is one of three elements the existence of which was predicted in 1871 by the Russian chemist Dmitry Ivanovich Mendeleyev when he first devised his periodic table. Not until 1886, however, was germanium identified as one of the elements in a newly found mineral.

The origins of tin also are lost in antiquity. Apparently, bronzes, which are copper–tin alloys, were used by man in prehistory long before pure tin metal itself was isolated. Bronzes were common in early Mesopotamia, the Indus Valley, Egypt, Crete, Israel, and Peru. Much of the tin used by the early Mediterranean peoples apparently came from the Scilly Islands and from Cornwall in the British Isles, where tin mining dates to at least 300–200 BC. Tin mines were operating in both the Inca and Aztec domains of South and Central America before the Spanish conquest.

Lead is mentioned often in early Biblical accounts. The Babylonians used the metal as plates on which to record inscriptions. The Romans used it for tablets, water pipes, coins, and even cooking utensils; indeed, as a result of the last use, lead poisoning was recognized in the time of Augustus Caesar. The compound known as white lead was apparently prepared as a decorative pigment at least as early as 200 BC. Modern developments date to the exploitation in the late 1700s of deposits in the Missouri–Kansas–Oklahoma area in the United States.

Comparative chemistry

In the periodic table, the elements with eight electrons outermost form the group known as the noble gases (Group 0), the least reactive of the elements. The carbon group elements (Group IVa), with four electrons, occupy a middle position. Elements to the left of Group IVa have fewer than four electrons in the valence shell and tend to lose them (with their negative charges) to become positively charged ions, represented by the symbol for the element with a superscript indicating the number and sign of the charges; such elements are called metals. The nonmetals (except boron) are in the groups to the right of Group IVa; each has more than four electrons in its outermost shell and tends to acquire electrons to complete its octet, forming negatively charged ions.



General properties of the group


Crystal structure



All the carbon group elements and many of their compounds have important uses. Carbon as diamond, for example, is the most expensive and brilliant of all the natural gemstones and also the hardest of abrasives; carbon as graphite is important as electrodes in electrochemical cells, as a lubricant, and, in microcrystalline and nearly amorphous form, as a black pigment, an adsorbent, a fuel, a filler for rubber, and in pencils. Coals are elemental carbon mixed with varying amounts of carbon compounds; coke and charcoal are nearly pure carbon. All organic compounds, such as proteins, carbohydrates, and fats, contain carbon, and all plant and animal cells consist of carbon compounds and their polymers. (Polymers are macromolecules consisting of many simple molecules bonded together in specific ways.) Carbonate minerals are important sources of various metals, such as sodium, magnesium, calcium, copper, and lead.

Elemental silicon is important largely as a semiconductor. Silica (silicon dioxide) is useful as an abrasive, in the production of glass and other ceramic bodies, as an adsorbent, and as sand in mortars and concretes; and these are only a few of its applications. Both naturally occurring and synthetically produced silicates are important in ceramics, building materials, absorbents, and ion exchangers.

Applications of germanium have been limited to semiconducting devices, indicating its weak metallic nature.

Tin-plating of iron protects the latter from corrosion; tin piping and valves maintain purity in water and beverages; molten tin is the base for (float) plateglass production; and tin is a significant component of such alloys as bronzes, pewter, bearing metals, type metals, and lead-based solders. Tin exists in two oxidation states; tin(IV) oxide is , +4 and +2. Tin oxide, in which tin is in the +4 state, is useful in making ceramic bodies opaque, as a mild abrasive, and as a weighting agent for fabrics; tin(II) . Tin fluoride and tin (II) pyrophosphate pyrophosphate, in which tin is in the +2 state, are used in dentifrices. Organic tin compounds act as stabilizers in certain plastics and as wood preservatives.

Elemental lead finds extensive use. Together with the compound lead oxide (IVPbO2) oxide and with lead–antimony or lead–calcium alloys, it is employed in common storage batteries. Type metals, bearing alloys, shot metal, and fusible alloys all contain lead. Tetraethyllead is the most important antiknock additive to motor fuels.

Electron configurations





Atomic size

Reference has been made to some of the physical properties of the carbon group elements (see Table). Most of the variations in properties from carbon through lead parallel increase in atomic size and are comparable with those of elements in the boron, nitrogen, oxygen, and fluorine groups. The general trends apparent in the Table are roughly those found for the adjacent boron group and nitrogen group elements. The significantly higher melting and boiling points of the carbon group elements reflect their tendency to exist as giant molecules, as opposed to the tendencies of elements in the adjacent families to exist as smaller, discrete molecules.




Biological and physiological significance

The biological implications of carbon are so extensive that they can be discussed here only very briefly. All biological substances are based upon compounds in which carbon is combined with other elements, the nature of the combination determining the characteristics, function, and relative importance of the substance. To begin with the inorganic compounds of carbon, elemental carbon is nontoxic. Carbon monoxide (CO) is both more readily absorbed and more firmly bound to the hemoglobin of the blood than is oxygen and is thus, even in small concentrations, a dangerous asphyxiant. Carbon dioxide (CO2) is an asphyxiant of significance only in relatively large concentrations; in small concentration, it stimulates breathing. Hydrogen cyanide (HCN) and its derivatives (cyanogen compounds, cyanides) are all very toxic as protoplasmic poisons through the inhibition of tissue oxidation. Carbon tetrachloride (CCl4) and other chlorinated hydrocarbons damage the nervous system. Among organic compounds, the most toxic are derivatives that contain the halogen elements (fluorine, chlorine, bromine and iodine), sulfur, selenium, tellurium, nitrogen, phosphorus, arsenic, lead, and mercury. Most organometallic compounds are toxic, while oxygen-containing derivatives of the hydrocarbons are usually less toxic.


The toxicology of germanium and its compounds is poorly defined.

Elemental tin is apparently nontoxic, and quantities of tin up to 300 parts per million, as dissolved by foods packaged in tin-plated containers and cooking utensils, are not harmful. Organic tin compounds, however, commonly used as biocides and fungicides, are toxic to human beings.

Although elemental In general, lead and difficultly soluble lead compounds are not absorbed by human tissue and are, therefore, quite innocuous, any soluble lead compound is its compounds are toxic, with toxicity of the compound increasing as its solubility increases. Symptoms of lead poisoning include abdominal pain and diarrhea followed by constipation, nausea, vomiting, dizziness, headache, and general weakness. Elimination of contact with a lead source is normally sufficient to effect a cure. The elimination of lead from insecticides and paint pigments and the use of respirators and other protective devices in areas of exposure have reduced lead poisoning materially. Low-level atmospheric and water pollution, stemming largely from The recognition that the use of tetraethyllead , [Pb(C2H5)4] in motor fuels, has been receiving increasing attentionas an antiknock additive in gasoline was polluting the air and water led to the compound’s elimination as a gasoline constituent in the 1980s.

Individual carbon group elements


Occurrence and distribution


Production of elemental carbon

Elemental carbon is best considered in terms of its several crystalline forms—diamond, graphite, and “amorphous carbon”—since the widely different properties of these three substances require different approaches. (When an element exists in more than one crystal form, each is called an allotrope.)




Amorphous carbon, which is solid but not clearly crystallized, probably consists of microcrystals of graphite; it is common in commerce as coke; lampblack, or carbon black; and charcoal. These products are obtained by heating coal (to give coke), natural gas (to give blacks), or carbonaceous material of vegetable or animal origin, such as wood or bone (to give charcoal), at elevated temperatures in the presence of insufficient oxygen to allow combustion. The volatile by-products are recovered and used separately.

Structure of carbon allotropes




The temperature and pressure relationships of any substance can be plotted to show how, for example, the boiling point changes as pressure is changed; such graphs are called phase diagrams. They reveal conditions under which rearrangements in the atomic or molecular structure of a substance take place.The crystal structure of graphite is of a kind that permits the formation of many compounds, called lamellar or intercalation compounds, by penetration of molecules or ions. Graphitic oxide and graphitic fluoride are nonconducting lamellar substances not obtained in true molecular forms that can be reproduced, but their formulas do approximate, respectively, the compositions of carbon dioxide and carbon monofluoride.


Nuclear properties







Biological implications

The biological implications of the element and its simple compounds have been discussed earlier; the most significant implications are associated with organic compounds, which are discussed in such articles as chemical compound.





Occurrence and distribution

On a weight basis, the abundance of silicon in the crust of the Earth is exceeded only by oxygen. Estimates of the cosmic abundance of other elements often are cited in terms of the number of their atoms per 106 atoms of silicon. Only hydrogen, helium, oxygen, neon, nitrogen, and carbon exceed silicon in cosmic abundance. Silicon is believed to be a cosmic product of alpha-particle absorption, at a temperature of about 109 K, by the nuclei of carbon-12, oxygen-16, and neon-20. The energy binding the particles that form the nucleus of silicon is about 8.4 million electron volts (MeV) per nucleon (proton or neutron). Compared with the maximum of about 8.7 million electron volts for the nucleus of iron, almost twice as massive as that of silicon, this figure indicates the relative stability of the silicon nucleus. The pure element silicon is too reactive to be found in nature. In compounds, the oxidized form, as silicon dioxide and particularly as silicates, is common in the Earth’s crust and is an important component of the Earth’s mantle. Silicon dioxide occurs both in crystalline minerals (e.g., quartz, cristobalite, tridymite) and amorphous or seemingly amorphous minerals (e.g., agate, opal, chalcedony) in all land areas. The natural silicates are characterized by their abundance, wide distribution, and structural and compositional complexities. Most of the elements of the following groups in the periodic table are found in silicate minerals: groups Ia, IIa, IIIa, IIIb, IVb, Vb, VIb, VIIa. These elements are said to be lithophilic, or stone-loving. Important silicate minerals include the clays, feldspar, olivine, pyroxene, amphiboles, micas, and zeolites.

Production of elemental silicon

Elemental silicon is produced commercially by the reduction of silica (SiO2) with coke in an electric furnace, and the impure product is then refined. Almost pure silicon is obtained by the reduction of silicon tetrachloride or trichlorosilane. For use in electronic devices, single crystals are grown by slowly withdrawing seed crystals from molten silicon.

Properties of the element

The more important physical and chemical properties of silicon have been summarized and related to the ground-state electronic configuration of the silicon atom and the position of silicon in the periodic table. Because silicon forms chains similar to those formed by carbon, silicon has been studied as a possible base element for silicon organisms. The limited number of silicon atoms that can catenate, however, greatly reduces the number and variety of silicon compounds compared with those of carbon. Another property resulting from the electronic structure of silicon is that it functions as an intrinsic semiconductor (see crystal: Electric properties). Addition of an element such as boron, an atom of which can be substituted for a silicon atom in the crystal structure but which provides one less valence electron (boron is an acceptor atom) than silicon, allows silicon atoms to lose electrons to it. The positive holes created by the shift in electrons allow extrinsic semiconduction of a type referred to as positive (p). Addition of an element such as arsenic, an atom of which can also be substituted for a silicon atom in the crystal but which provides an extra valence electron (arsenic is a donor atom), releases its electron within the lattice. These electrons allow semiconduction of the negative (n) type. If p-silicon and n-silicon wafers are joined, in a manner called the pn junction, and placed in sunlight, the absorbed energy causes electrons to move across the junction and an electric current to flow in an external circuit connecting the two wafers. Such a solar cell is a source of energy for space devices.

Unlike carbon, the only crystalline form in which silicon exists is an octahedral form based upon atoms in the diamond-type arrangement. The amorphous forms of silicon contain micro crystals of this type. The reduced bond energy in crystalline silicon renders the element lower melting, softer, and chemically more reactive than diamond.


As is true with carbon, the bonds in elemental silicon are strong enough to require large energies to activate, or promote, reaction in an acidic medium, and the oxidation–reduction reactions do not appear to be reversible at ordinary temperatures.


The name germanium derives from the Latin word Germania (Germany) and was given to the element by its German discoverer, Clemens Winkler, in 1886.

Occurrence and distribution

On a weight basis, germanium is a scarce but not an extremely rare element in the crust of the Earth, equalling in abundance beryllium, molybdenum, and cesium and exceeding the elements arsenic, cadmium, antimony, and mercury. In the Cosmos, the atomic abundance of germanium is 50.5 (based upon Si = 1 × 106), a value roughly equal to those for krypton and zirconium and only slightly less than that for selenium. The cosmic abundance is much less than those of a number of the heavier elements; e.g., bromine, strontium, tin, barium, mercury, and lead. All of the elements of lower nuclear charge than germanium, except beryllium, boron, scandium, and gallium, are cosmically more abundant than germanium. Cosmically, germanium is believed to be one of the many elements formed by neutron absorption after the initial processes of hydrogen and helium burning and alpha-particle absorption.

Germanium is widely distributed in nature but is too reactive to occur free. Primary minerals include argyrodite, germanite, renierite, and canfieldite, all of them rare; only germanite and renierite have been used as commercial sources for the element. Trace quantities of germanium are found in certain zinc blendes, in sulfidic ores of copper and arsenic, and in coals, the latter possibly a consequence of the concentration of the element by plants of the Carboniferous Period in geologic history. Certain present-day plants are known to concentrate germanium. Both zinc-process concentrates and ash and flue dusts from coal-burning installations provide commercial sources of germanium.

Production of germanium

Pure germanium is obtained from these sources in a complicated process that finally yields billets or blocks, which may be purified by further refining to the quality required for the manufacture of semiconductors. Single crystals of germanium are grown in an atmosphere of nitrogen or helium from the molten material. These are then transformed into semiconductors by being doped (infused) with electron donor or acceptor atoms, either by incorporating the impurities in the melt during growth of the crystal or by diffusing the impurities into the crystal after it has been formed.

Properties of the element

The physical and chemical properties of germanium have been summarized earlier. Like silicon, germanium crystallizes in the diamond type of structure. The trend in properties noted with silicon and related to reduced bond energy continues with germanium. The electrical and semiconducting characteristics of germanium are comparable to those of silicon.

Germanium (II) compounds compounds in which germanium is in the +2 oxidation state are well characterized as solids, and in general they are readily oxidized. Elemental germanium can be electrodeposited from many solutions and melts of its compounds. It is of interest that as little as one milligram of dissolved germanium per litre seriously interferes with the electrodeposition of zinc.


The symbol Sn for tin is an abbreviation of the Latin word for tin, stannum.

Occurrence and distribution

On a weight basis, tin is a scarce but not rare element in the crust of the Earth, its abundance being of the same order of magnitude as such technically useful elements as cobalt, nickel, copper, cerium, and lead, and it is essentially equal to the abundance of nitrogen. In the Cosmos, there are 1.33 atoms of tin per 1 × 106 atoms of silicon, an abundance roughly equal to that of niobium, ruthenium, neodymium, or platinum. Cosmically, tin is a product of neutron absorption. Its richness in stable isotopes is noteworthy.

The only mineral of commercial significance is cassiterite (SnO2). No high-grade deposits are known. The major sources are alluvial deposits, averaging about 0.01 percent tin. Lode deposits, containing up to 4 percent, are found in Bolivia and Cornwall. The latter were worked at least as early as Phoenician times but are no longer of major consequence. Some 90 percent of world production comes from Malaysia, Thailand, Indonesia, Bolivia, Congo (Brazzaville), Nigeria, and China. The United States has no significant deposits. (For commercial production see tin processing.)

Properties of the element

The major physical and chemical properties of tin have been summarized earlier. The relationships among the allotropic modifications of tin can be represented as transformations from one crystal type to another at specific temperatures:

(The double arrows signify that the transformation occurs in both directions, as tin is heated or as it is cooled.) Gray tin is easily crumbled, whereas white tin is malleable and ductile. The spontaneous conversion of the bright metal to a gray powder at low temperatures (“tin pest”) seriously hampers the use of the metal in very cold regions. This change is rapid only below −50° C, unless catalyzed by gray tin or tin (IV)in the +4 oxidation state. As a consequence of internal friction, white tin emits a characteristic sound (“tin cry”) when bent. Elemental tin is readily oxidized to the dipositive ion in acidic solution, but this tin(II) Sn2+ ion is converted to tin(IV) the Sn4+ ion by many mild oxidizing agents, including elemental oxygen. Oxidation under alkaline conditions normally gives the tetrapositive (Sn4+) state. In an alkaline medium, dipositive tin (Sn2+) disproportionates readily to tetrapositive tin and the free element.



Occurrence and distribution

On a weight basis, lead has nearly the same abundance in the Earth’s crust as tin. Cosmically, there is 0.47 lead atom per 106 silicon atoms. The cosmic abundance is comparable with those of cesium, praseodymium, hafnium, and tungsten, each of which is regarded as a reasonably scarce element. Lead is formed both by neutron-absorption processes and the decay of radionuclides of heavier elements. Stable lead nuclides are the end products of radioactive decay in the three natural decay series: uranium (decays to lead-206), thorium (decays to lead-208), and actinium (decays to lead-207).

Although lead is not abundant, natural concentration processes have resulted in substantial deposits of commercial significance, particularly in the United States, but also in Canada, Africa, Australia, Spain, Germany, and South America. Significant deposits are found in the U.S. in the western states and the Mississippi Valley. Elemental lead is only rarely found in nature. The major minerals are galena (PbS), anglesite (PbSO4), and cerussite (PbCO3). (For commercial production see lead processing.)

Properties of the element

The major physical and chemical properties of lead and their relationships to electronic configuration and position in the periodic table have been summarized earlier. Only a single crystalline modification, with a close-packed metallic lattice, is known. Properties that are responsible for the many uses of elemental lead include its ductility, ease of welding, low melting point, high density, and ability to absorb gamma radiation and X radiation. Molten lead is an excellent solvent and collector for elemental silver and gold. The structural applications of lead are limited by its low tensile and fatigue strengths and its tendency to flow even when only lightly loaded. Elemental lead can be oxidized to lead(II) the Pb2+ ion by hydrogen ionions, but the insolubility of most lead(II) salts salts of Pb2+ makes lead resistant to attack by many acids. Oxidation under alkaline conditions is easier to effect and is favoured by the formation of the soluble lead(II) speciesspecies of lead in the +2 oxidation state. Lead (IV) oxide oxide (PbO2, with lead as the Pb4+ ion) is among the stronger oxidizing agents in acidic solution, but it is comparatively weak in alkaline solution. The ease of oxidation of lead is enhanced by complex formation. The electrodeposition of lead is best effected from aqueous solutions containing lead (II) hexafluorosilicate (IV) and hexafluorosilicic acid.

Nuclear properties
