Carbon group - WikiHQ

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The carbon group is a periodic table group consisting of carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and flerovium (Fl). It lies within the p-block.

In modern IUPAC notation, it is called group 14. In the field of semiconductor physics, it is still universally called group IV. The group is also known as the tetrels (from the Greek word tetra, which means four), stemming from the Roman numeral IV in the group name, or (not coincidentally) from the fact that these elements have four valence electrons (see below). They are also known as the crystallogens or adamantogens.

Characteristics

Chemical

Like other groups, the members of this family show patterns in electron configuration, especially in the outermost shells, resulting in trends in chemical behavior:

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!Z !! Element !! Electrons per shell

| 6 || Carbon || 2, 4

| 14 || Silicon || 2, 8, 4

| 32 || Germanium || 2, 8, 18, 4

| 50 || Tin || 2, 8, 18, 18, 4

| 82 || Lead || 2, 8, 18, 32, 18, 4

| 114 || Flerovium || 2, 8, 18, 32, 32, 18, 4 (predicted)

Each of the elements in this group has 4 electrons in its outer shell. An isolated, neutral group 14 atom has the ns2 np2 configuration in the ground state. These elements, especially carbon and silicon, have a strong propensity for covalent bonding, which usually brings the outer shell to eight electrons. Bonds in these elements often lead to hybridisation where distinct s and p characters of the orbitals are erased. For single bonds, a typical arrangement has four pairs of sp3 electrons, although other cases exist too, such as three sp2 pairs in graphene and graphite. Double bonds are characteristic for carbon (alkenes, ...); the same for π-systems in general. The tendency to lose electrons increases as the size of the atom increases, as it does with increasing atomic number.

Carbon alone forms monatomic anions, in the form of carbide (C4−, also called methanide); the other carbon group elements form Zintl ions with electropositive metals such as magnesium.

Silicon and germanium, both metalloids, each can form +4 ions.

Tin and lead both are metals, while flerovium is a synthetic, radioactive (its half-life is very short, only 1.9 seconds) element that may have a few noble gas-like properties, though it is still most likely a post-transition metal. Tin and lead are both capable of forming +2 ions. Although tin is typically considered a metal, its α allotrope looks more like germanium than like a metal and it is a poor electric conductor.

Among main group (groups 1, 2, 13–17) alkyl derivatives QRn, where n is the standard bonding number for Q (see lambda convention), the group 14 derivatives QR4 are notable in being electron-precise: they are neither electron-deficient (having fewer electrons than an octet and tending to be Lewis acidic at Q and usually existing as oligomeric clusters or adducts with Lewis bases) nor electron-excessive (having lone pair(s) at Q and tending to be Lewis basic at Q). As a result, the group 14 alkyls have low chemical reactivity relative to the alkyl derivatives of other groups. In the case of carbon, the high bond dissociation energy of the C–C bond and lack of electronegativity difference between the central atom and the alkyl ligands render the saturated alkyl derivatives, the alkanes, particularly inert.

Carbon forms tetrahalides with all the halogens. Carbon also forms many oxides such as carbon monoxide, carbon suboxide, and carbon dioxide. Carbon forms a disulfide an a diselenide.

Silicon forms several hydrides; two of them are SiH4 and Si2H6. Silicon forms tetrahalides with fluorine (SiF4), chlorine (SiCl4), bromine (SiBr4), and iodine (SiI4). Silicon also forms a dioxide and a disulfide. Silicon nitride has the formula Si3N4.

Tin forms two hydrides: SnH4 and Sn2H6. Tin forms dihalides and tetrahalides with all halogens except astatine. Tin forms monochalcogenides with naturally occurring chalcogens except polonium, and forms dichalcogenides with naturally occurring chalcogens except polonium and tellurium.

Lead forms one hydride, which has the formula PbH4. Lead forms dihalides and tetrahalides with fluorine and chlorine, and forms a dibromide and a diiodide, although the tetrabromide and tetraiodide of lead are unstable. Lead forms four oxides, a sulfide, a selenide, and a telluride.

There are no known compounds of flerovium.

Physical

The boiling points of the carbon group tend to get lower with the heavier elements. At standard pressure, carbon, the lightest carbon group element, sublimes at 3825 °C. Silicon's boiling point is 3265 °C, germanium's is 2833 °C, tin's is 2602 °C, and lead's is 1749 °C. Flerovium is predicted to boil at −60 °C. The melting points of the carbon group elements have roughly the same trend as their boiling points. Silicon melts at 1414 °C, germanium melts at 939 °C, tin melts at 232 °C, and lead melts at 328 °C.

Carbon's crystal structure is hexagonal; at high pressures and temperatures it forms diamond (see below). Silicon and germanium have diamond cubic crystal structures, as does tin at low temperatures (below 13.2 °C). Tin at room temperature has a tetragonal crystal structure. Lead has a face-centered cubic crystal structure.

Silicon has two known allotropes that exist at room temperature. These allotropes are known as the amorphous and the crystalline allotropes. The amorphous allotrope is a brown powder. The crystalline allotrope is gray and has a metallic luster.

Tin has two allotropes: α-tin, also known as gray tin, and β-tin. Tin is typically found in the β-tin form, a silvery metal. However, at standard pressure, β-tin converts to α-tin, a gray powder, at temperatures below . This can cause tin objects in cold temperatures to crumble to gray powder in a process known as tin pest or tin rot.

Lead makes up 14 parts per million of the Earth's crust, making it the 36th most abundant element there. On average, lead makes up 23 parts per million of soil, but the concentration can reach 20000 parts per million (2 percent) near old lead mines. Lead exists in seawater at concentrations of 2 parts per trillion. Lead makes up 1.7 parts per million of the human body by weight. Human activity releases more lead into the environment than any other metal.

Silicon as silica in the form of rock crystal 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 BCE – and by the Phoenicians. Many of the naturally occurring compounds or silicate minerals were used in various kinds of mortar for construction of dwellings by the earliest people.

The origins of tin seem to be lost in history. It appears that bronzes, which are alloys of copper and tin, were used by prehistoric man some time before the pure metal 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 Isles and Cornwall in the British Isles, where mining of the metal dates from about 300–200 BCE. Tin mines were operating in both the Inca and Aztec areas 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 BCE.

Modern discoveries

Amorphous elemental silicon was first obtained pure 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.

Germanium is one of three elements the existence of which was predicted in 1869 by the Russian chemist Dmitri Mendeleev when he first devised his periodic table. However, the element was not actually discovered for some time. In September 1885, a miner discovered a mineral sample in a silver mine and gave it to the mine manager, who determined that it was a new mineral and sent the mineral to Clemens A. Winkler. Winkler realized that the sample was 75% silver, 18% sulfur, and 7% of an undiscovered element. After several months, Winkler isolated the element and determined that it was element 32.

Silicon dioxide has a wide variety of applications, including toothpaste, construction fillers, and silica is a major component of glass. 50% of pure silicon is devoted to the manufacture of metal alloys. 45% of silicon is devoted to the manufacture of silicones. Silicon is also commonly used in semiconductors and has been since the 1950s.

Production

Carbon's allotrope diamond is produced mostly by Russia, Botswana, Congo, Canada, South Africa, and India. 80% of all synthetic diamonds are produced by Russia. China produces 70% of the world's graphite. Other graphite-mining countries are Brazil, Canada, and Mexico. Carbon's importance to life is primarily due to its ability to form numerous bonds with other elements. There are 16 kilograms of carbon in a typical 70-kilogram human.

A biological role for germanium is not known, although it does stimulate metabolism. In 1980, germanium was reported by Kazuhiko Asai to benefit health, but the claim has not been proven. Some plants take up germanium from the soil in the form of germanium oxide. These plants, which include grains and vegetables contain roughly 0.05 parts per million of germanium. The estimated human intake of germanium is 1 milligram per day. There are 5 milligrams of germanium in a typical 70-kilogram human.

Some tin compounds are toxic to ingest, but most inorganic compounds of tin are considered nontoxic. Organic tin compounds, such as trimethyltin and triethyltin are highly toxic, and can disrupt metabolic processes inside cells.