Introduction group IVA

Group IVA includes following elements: Carbon - [C], Silicon - [Si], Germanium - [Ge], Tin - [Sn], Lead - [Pb].

Carbon

Carbon was known as a substance in prehistory (charcoal, soot) though its recognition as an element came much later, being the culmination of several experiments in the eighteenth century. Diamond and graphite were known to be different forms of the element by the close of the eighteenth century, and the relationship between carbon, carbonates, carbon dioxide, photosynthesis in plants, and respiration in animals was also clearly delineated by this time. The great upsurge in synthetic organic chemistry began in the 1830s and various structural theories developed following the introduction of the concept of valency in the 1850s.

The first metal carbonyl compounds Ni(CO)4 and Fe(CO)5 were prepared and characterized by L. Mond and his group in 1889-91 and this work has burgeoned into the huge field of metal carbonyl cluster compounds which is still producing results of fundamental importance. Even more extensive is the field of organometallic chemistry which developed rapidly after the seminal papers on the “sandwich” structure of ferrocene and the “TC bonding” of ethylene complexes. The constricting influence of classical covalentbond theory was finally overcome when it was realized that carbon in many of its compounds can be 5-coordinate (Al2Me6, Me - methyl), 6-coordinate (C2B10H12) or even 7-coordinate (Li4Me4, Me - methyl). In parallel with these developments in synthetic chemistry and bonding theory have been technical and instrumental advances of great significance; foremost amongst these have been the development of 14C radioactive dating techniques, the commercial availability of 13C NMR instruments in the early 1970s, and the industrial production of artificial diamonds. The most exciting recent development in the chemistry of carbon has been the intriguing discovery of a whole new range of soluble molecular forms of elemental carbon, the fullerenes, of which C60 and C70 are the most prominent members. This was recognized by the 1996 Nobel Prize for Chemistry.

Silicon

Silicon shows a rich variety of chemical properties and it lies at the heart of much modern technology. Indeed, it ranges from such bulk commodities as concrete, clays and ceramics, through more chemically modified systems such as soluble silicates, glasses and glazes to the recent industries based on silicone polymers and solidstate electronics devices. The refined technology of ultrapure silicon itself is perhaps the most elegant example of the close relation between chemistry and solid-state physics and has led to numerous developments such as the transistor, printed circuits and microelectronics.

In its chemistry, silicon is clearly a member of Group 14 of the periodic classification but there are notable differences from carbon, on the one hand, and the heavier metals of the group on the other. Silica (SiO2) and silicates have been intimately connected with the evolution of mankind from prehistoric times: the names derive from the Latin silex, gen. silicis, flint, and serve as a reminder of the simple tools developed in Paleolithic times (~500 000 years ago) and the shaped flint knives and arrowheads of the neolithic age which began some 20 000 years ago. The name of the element, silicon, was proposed by Thomas Thomson in 1831, the ending on being intended to stress the analogy with carbon and boron.

The great affinity of silicon for oxygen delayed its isolation as the free element until 1823 when J. J. Berzelius succeeded in reducing K2SiF6 with molten potassium. He first made SiCl4 in the same year, SiF4 having previously been made in 1771 by C. W. Scheele who dissolved SiO2 in hydrofluoric acid. The first volatile hydrides were discovered by F. Wohler who synthesized SiHCl3 in 1857 and SiH4 in 1858, but major advances in the chemistry of the silanes awaited the work of A. Stock during the first third of the twentieth century. Likewise, the first organosilicon compound SiEt4 (Et - ethil) was synthesized by C. Friedel and J. M. Crafts in 1863, but the extensive development of the field was due to F. S. Kipping in the first decades of this century. The unique properties and industria1 potential of siloxanes escaped attention at that time and the dramatic development of silicone polymers, elastomers, and resins has occurred during the past decades.

Germanium. Tin. Lead.

Germanium was predicted as the missing element of a triad between silicon and tin by J. A. R. Newlands in 1864, and in 1871 D. I. Mendeleev specified the properties that “ekasilicon” would have. The new element was discovered by C. A. Winkler in 1886 during the analysis of a new and rare mineral argyrodite, Ag8GeS6; he named it in honour of his country, Germany. By contrast, tin and lead are two of the oldest metals known to man and both are mentioned in early books of the Old Testament. The chemical symbols for the elements come from their Latin names stannum and plumbum. Lead was used in ancient Egypt for glazing pottery (7000 - 5000 BC); the Hanging Gardens of Babylon were floored with sheet lead to retain moisture and the Romans used lead extensively for water-pipes and plumbing; they extracted some 6 - 8 million tonnes in four centuries with a peak annual production of 60 000 tonnes. Production of tin, though equally influential, has been on a more modest scale and dates back to 3500-3200 BC. Bronze weapons and tools containing 10-15% Sn alloyed with Cu have been found at Ur, and Pliny described solder as an alloy of Sn and Pb in AD 79.

Germanium and Sn are non-toxic (like C and Si). Lead is now recognized as a heavy-metal poison; it acts by complexing with oxo-groups in enzymes and affects virtually all steps in the process of haem synthesis and porphyrin metabolism. It also inhibits acetylcholineesterase, acid phosphatase, ATPase, carbonic anhydrase, etc. and inhibits protein synthesis probably by modifying transfer-RNA. Typical symptoms of lead poisoning are cholic, anaemia, headaches, convulsions, chronic nephritis of the kidneys, brain damage and central nervous-system disorders.

 

Did you know?

Noble gases are in group 18 of the periodic table.