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:
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, CO2...); 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. Germanium forms five hydrides. The first two germanium hydrides are GeH4 and Ge2H6. Germanium forms tetrahalides with all halogens except astatine and forms dihalides with all halogens except bromine and astatine. Germanium bonds to all natural single chalcogens except polonium, and forms dioxides, disulfides, and diselenides. Germanium nitride has the formula Ge3N4. 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. The densities of the carbon group elements tend to increase with increasing atomic number. Carbon has a density of 2.26 g·cm−3; silicon, 2.33 g·cm−3; germanium, 5.32 g·cm−3; tin, 7.26 g·cm−3; lead, 11.3 g·cm−3. The atomic radii of the carbon group elements tend to increase with increasing atomic number. Carbon's atomic radius is 77 picometers, silicon's is 118 picometers, germanium's is 123 picometers, tin's is 141 picometers, and lead's is 175 picometers.
Allotropes
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