Group 14

Element number 114: flerovium (symbol Fl) and element number 116: livermorium (symbol Lv)

The International Union of Pure and Applied Chemistry (IUPAC) has recommended names for elements 114 and 116. Scientists from the Lawrence Livermore National Laboratory (LLNL) and at Dubna proposed the names as Flerovium for element 114 and Livermorium for element 116.

Flerovium (atomic symbol Fl) was chosen to honor Flerov Laboratory of Nuclear Reactions, where superheavy elements, including element 114, were synthesized. Georgiy N. Flerov (1913-1990) was a renowned physicist who discovered the spontaneous fission of uranium and was a pioneer in heavy-ion physics. He is the founder of the Joint Institute for Nuclear Research. In 1991, the laboratory was named after Flerov - Flerov Laboratory of Nuclear Reactions (FLNR).

Livermorium (atomic symbol Lv) was chosen to honor Lawrence Livermore National Laboratory (LLNL) and the city of Livermore, Calif. A group of researchers from the Laboratory, along with scientists at the Flerov Laboratory of Nuclear Reactions, participated in the work carried out in Dubna on the synthesis of superheavy elements, including element 116. (Lawrencium -- Element 103 -- was already named for LLNL's founder E.O. Lawrence.)

In 1989, Flerov and Ken Hulet (1926-2010) of LLNL established collaboration between scientists at LLNL and scientists at FLNR; one of the results of this long-standing collaboration was the synthesis of elements 114 and 116.

The creation of elements 116 and 114 involved smashing calcium ions (with 20 protons each) into a curium target (96 protons) to create element 116. Element 116 decayed almost immediately into element 114. The scientists also created element 114 separately by replacing curium with a plutonium target (94 protons).

The creation of elements 114 and 116 generate hope that the team is on its way to the "island of stability," an area of the periodic table in which new heavy elements would be stable or last long enough for applications to be found.

The new names were submitted to the IUPAC in late October. The new names will not be official until about five months from now when the public comment period is over.

The Group 14 elements

Group 14 periodicity

This article addresses the periodicity displayed by the Group 14 elements but excluding, largely, ununquadium (element 114) about which virtually nothing is known. One could predict the properties of ununquadium based upno those of the higher elements and this is left as an exercise for the reader.

Nature of the elements

The elements become increasingly metallic down the group. Carbon, at the top, is a typical non-metal while silicon is a semiconductor profoundly important to the electronics industries. Tin and lead are very metallic although one modification of tin known as grey tin has the same diamond structure as does germanium and silicon. The elements lower down the group form complexes while carbon does not. The melting points of the elements decrease down the group as the elements become increasingly metallic.

Multiple bonds

Carbon often forms multiple bonds, both with itself (as in ethene and ethyne) and with other elements such as oxygen (as in carbon dioxide and ketones). In contrast, silicon, germanium, and tin only form analogues of ethene (albeit non-planar) when the elements possess bulky substituents. While the C=C π-bond formed through the overlap of C 2p-orbitals is strong, those lower down the group are much less strong. This also explains why graphite is stable while there are no analogues of graphite lower down the group. Carbon dioxide, CO2, possesses two carbon-oxygen double bonds (O=C=O) while the corresponding silicon dioxide, SiO2, possesses an extended lattice structure. This is because the π-bond formed through the overlap of p-orbitals on carbon and oxygen is strong as the overlap is favourable, while lower down the group the π-overlap is less efficient.

Hydrides

The hydrides MX4 are known for all the elements except ununquadium although the lead compound (plumbane, PbH4) is poorly characterized. Each is a covalent molecule. The parent hydride for carbon is methane, CH4, and there is an extensive range of compounds called alkanes of the type CnH2n+2 (methane, ethane, propane, butane....). There are relatively few of the corresponding silicon hydrides (silanes) and they are spontaneously flammable. The germane GeH4 is known while the stannane SnH4, a colourless gas, decomposes to tin at about 0°C.

Halides

Two types of halide for this group are known: MX2 and MX4. The M(IV) halides dominate the top of the group while the M(II) halides dominate at the bottom. All the M(IV) halides MX4 (M = C, Si, Ge; X = F, Cl, Br, I) are all known for the three elements carbon, silicon, and germanium at the top of the group. However, as the group is descended, the stability of the M(II) state increases relative to the M(IV) state. None of the dihalides MX2 exist independently for carbon or silicon while most of the divalent halides MX2 are known for germanium in addition to the germanium tetrahalides. At the bottom of the group the most stable lead halides are PbX2 and the only known tetrahalide seems to be PbCl4 (this decomposes exothermically to PbCl2 and chlorine gas).

Oxides

Ionization Energy

ionization energies for Group 14 elements
Plot of the Group 14 ionization energies.

  • Carbon: 1086.5 kJ mol-1
  • Silicon: 786.5 kJ mol-1
  • Germanium: 762 kJ mol-1
  • Tin: 708.6 kJ mol-1
  • Lead: 715.6 kJ mol-1

Carbon has the highest ionization energy in the group. The ionization energy for silicon is lower because the outermost electrons for silicon (3p) are further away from the nucleus than those of the 2p level for carbon. The 3p electrons are further away at silicon because of the higher principal quantum number and because of screening by the n=1 and n=2 level electrons.

The downwards trend continues for germanium, but less so. This is a consequence of the d-block elements within the periodic table. There are ten extra charge units on the nucleus because of these 3d elements and because the ten 3d electrons do not screen the nucleus that efficiently, the effective nuclear charge is higher than it would have been without the 3d-elements. Consequently, electrons from the 4p level are more difficult to remove and the ionization energy of germanium is therefore little different than that of silicon. The ionization energy of tin is a little higher than it might have been because of the inclusion of the 4d elements. The first ionization energy of lead is actually higher than that of tin rather than lower. This is because of the inclusion not only of the 5d elements but also the 4f elements (the lanthanoids). The 4f electrons screen the nucleus rather inefficiently from 6p electrons causing the effective nuclear charge to be quite high, to the extent that the ionization energy for lead is actually a little higher than that of tin.

Electronegativity

Group 14 Pauling electronegatviities
Plot of Group 14 Pauling electronegatviities.

Atomic size

Group 14 atomic radii
Plot of the Group 14 atomic radii

Group 14 melting points

Plot of the Group 14 melting points
Plot of the Group 14 melting points.

Group 14 boiling points

Plot of the Group 14 boiling point
Plot of the Group 14 boiling points.

Boiling point of the hydride

Plot of the Group 14 hydride boiling points
Plot of the Group 14 hydride boiling points.

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Periodic Table groups

In the standard form of the periodic table the s-block, p-block, and d-block elements are organised into 18 vertical columns called groups. These are labelled from 1 to 18 under current IUPAC numenclature.

Earlier labelling schemes (Trivial Group names)

For historical reasons some Groups have special names. Terms such as the "alkali metals" are in very common use whereas the term "pnictogens" is very much less common. Some of these special names are listed in the Table.

Special group names
Group Name
1 Alkali metals
2 Alakine earth metals
8/9/10 Platinum Group Metals
11 Coinage Metals
15 Pnictogens
16 Chalcogens
17 Halogens
18 Noble Gases, Inert Gases

In addition the elements 57-71 (lanthanum-lutetium) are referred to as the lanthanoids (lanthanides) and the elements 89-103 (actinium-lawrencium) are referred to as the actinoids (actinides). The elements Sc, Y, and the lanthanoids are sometimes referred to as the rare earths.

The s-, p-, and d-blocks contain a total of 18 groups. The latest recommendations from IUPAC (the International Union of Pure and Applied Chemistry) require that these be labelled 1 - 18 from left to right. This is a good recommendation in the sense that it is at least unambiguous.

Confusion in labelling schemes

There are two other ways of labelling the groups, and both use labels 1-8 (often in Roman numeral format) with further A and B labels. Unfortunately there is enormous confusion here. The two schemes are shown in the table below, underneath the new IUPAC scheme in the first row. It is easy to see the origins of the confusion!

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1A 2A 3A 4A 5A 6A 7A 8 1B 2B 3B 4B 5B 6B 7B 0
1A 2A 3B 4B 5B 6B 7B 8 1B 2B 3A 4A 5A 6A 7A 0

One of these systems is more common in America and the other in Europe but there is really only room for one convention on a small planet, which is where the IUPAC systems scores. These days most new books are printed with the IUPAC labels, but often one of the older conventions is given as well.

The point about confusion is important. If you really must use one of the two older formats, then you must define which you are using. Otherwise it's not clear whether Group 3B refers to the boron group or to the scandium group.

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Copyright 1993-2011 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.