Carbon group

The carbon group is a periodic table group consisting of carbon, silicon, germanium, tin, lead, and flerovium. 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, stemming from the Roman numeral IV in the group name, or from the fact that these elements have four valence electrons. 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:

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

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 ; 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 negative ions, in the form of carbide ions.
Silicon and germanium, both metalloids, each can form +4 ions.
Tin and lead both are metals, while flerovium is a synthetic, radioactive 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 chemically a metal, its α allotrope looks more like germanium than like a metal and it is a poor electric conductor.
Among main group alkyl derivatives QR_n, where n is the standard bonding number for Q, the group 14 derivatives QR₄ are notable in being electron-precise: they are neither electron-deficient nor electron-excessive. 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, chlorine, bromine, and iodine. 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. Silicon and germanium have diamond cubic crystal structures, as does tin at low temperatures. 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

Carbon has multiple allotropes. The most common is graphite, which is carbon in the form of stacked sheets. Another form of carbon is diamond, but this is relatively rare. Amorphous carbon is a third allotrope of carbon; it is a component of soot. Another allotrope of carbon is a fullerene, which has the form of sheets of carbon atoms folded into a sphere. A fifth allotrope of carbon, discovered in 2003, is called graphene, and is in the form of a layer of carbon atoms arranged in a honeycomb-shaped formation.
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.

Nuclear

At least two of the carbon group elements have magic nuclei, meaning that these elements are more common and more stable than elements that do not have a magic nucleus.

Isotopes

There are 15 known isotopes of carbon. Of these, three are naturally occurring. The most common is stable carbon-12, followed by stable carbon-13. Carbon-14 is a natural radioactive isotope with a half-life of 5,730 years.
23 isotopes of silicon have been discovered. Five of these are naturally occurring. The most common is stable silicon-28, followed by stable silicon-29 and stable silicon-30. Silicon-32 is a radioactive isotope that occurs naturally as a result of radioactive decay of actinides, and via spallation in the upper atmosphere. Silicon-34 also occurs naturally as the result of radioactive decay of actinides.
32 isotopes of germanium have been discovered. Five of these are naturally occurring. The most common is the stable germanium-74, followed by stable germanium-72, stable germanium-70, and stable germanium-73. Germanium-76 is a primordial radioisotope.
40 isotopes of tin have been discovered. 14 of these occur in nature. The most common is tin-120, followed by tin-118, tin-116, tin-119, tin-117, tin-124, tin-122, tin-112, and tin-114: all of these are stable. Tin also has four radioisotopes that occur as the result of the radioactive decay of uranium. These isotopes are tin-121, tin-123, tin-125, and tin-126.
38 isotopes of lead have been discovered. 9 of these are naturally occurring. The most common isotope is lead-208, followed by lead-206, lead-207, and lead-204: all of these are stable. 5 isotopes of lead occur from the radioactive decay of uranium and thorium. These isotopes are lead-209, lead-210, lead-211, lead-212 and lead-214.
6 isotopes of flerovium have been discovered, all from human synthesis. Flerovium's most stable isotope is flerovium-289, which has a half-life of 2.6 seconds.

Occurrence

Carbon accumulates as the result of stellar fusion in most stars, even small ones. Carbon is present in the Earth's crust in concentrations of 480 parts per million, and is present in seawater at concentrations of 28 parts per million. Carbon is present in the atmosphere in the form of carbon monoxide, carbon dioxide, and methane. Carbon is a key constituent of carbonate minerals, and is in hydrogen carbonate, which is common in seawater. Carbon forms 22.8% of a typical human.
Silicon is present in the Earth's crust at concentrations of 28%, making it the second most abundant element there. Silicon's concentration in seawater can vary from 30 parts per billion on the surface of the ocean to 2000 parts per billion deeper down. Silicon dust occurs in trace amounts in Earth's atmosphere. Silicate minerals are the most common type of mineral on earth. Silicon makes up 14.3 parts per million of the human body on average. Only the largest stars produce silicon via stellar fusion.
Germanium makes up 2 parts per million of the Earth's crust, making it the 52nd most abundant element there. On average, germanium makes up 1 part per million of soil. Germanium makes up 0.5 parts per trillion of seawater. Organogermanium compounds are also found in seawater. Germanium occurs in the human body at concentrations of 71.4 parts per billion. Germanium has been found to exist in some very faraway stars.
Tin makes up 2 parts per million of the Earth's crust, making it the 49th most abundant element there. On average, tin makes up 1 part per million of soil. Tin exists in seawater at concentrations of 4 parts per trillion. Tin makes up 428 parts per billion of the human body. Tin oxide occurs at concentrations of 0.1 to 300 parts per million in soils. Tin also occurs in concentrations of one part per thousand in igneous rocks.
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 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.
Flerovium doesn't occur in nature at all, so it only exists in particle accelerators with a few atoms at a time.