Post-transition metal

Being close to the metal-nonmetal border, their crystalline structures tend to show covalent or directional bonding effects, having generally greater complexity or fewer nearest neighbours than other metallic elements.

Elements 112–118 (copernicium, nihonium, flerovium, moscovium, livermorium, tennessine, and oganesson) may be post-transition metals; insufficient quantities of them have been synthesized to allow sufficient investigation of their actual physical and chemical properties.

[9] With some irregularities, atomic radii contract, ionisation energies increase,[8] fewer electrons become available for metallic bonding,[10] and "ions [become] smaller and more polarizing and more prone to covalency.

"[11] This phenomenon is more evident in period 4–6 post-transition metals, due to inefficient screening of their nuclear charges by their d10 and (in the case of the period 6 metals) f14 electron configurations;[12] the screening power of electrons decreases in the sequence s > p > d > f. The reductions in atomic size due to the interjection of the d- and f-blocks are referred to as, respectively, the 'scandide' or 'd-block contraction',[n 3] and the 'lanthanide contraction'.

"[14] Platinum is a moderately hard metal (MH 3.5) of low mechanical strength, with a close-packed face-centred cubic structure (BCN 12).

Like gold, platinum is a chalcophile element in terms of its occurrence in the Earth's crust, preferring to form covalent bonds with sulfur.

Stable compounds in which copper is in its less preferred oxidation state of +1 (Cu2O, CuCl, CuBr, CuI and CuCN, for example) have significant covalent character.

[29] Copper forms Zintl phases such as Li7CuSi2[30] and M3Cu3Sb4 (M = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, or Er).

[44] Gold oxide (Au2O3) is amphoteric, with acidic properties predominating; it forms anionic hydroxoaurates M[Au(OH)4], where M = Na, K, ½Ba, Tl; and aurates such as NaAuO2.

On the group 12 metals (zinc, cadmium and mercury), Smith[48] observed that, "Textbook writers have always found difficulty in dealing with these elements."

[61] Cadmium is a soft, ductile metal (MH 2.0) that undergoes substantial deformation, under load, at room temperature.

[74] Copernicium is expected to be a liquid at room temperature, although experiments have so far not succeeded in determining its boiling point with sufficient precision to prove this.

Like its lighter congener mercury, many of its singular properties stem from its closed-shell d10s2 electron configuration as well as strong relativistic effects.

Solid copernicium is expected to crystallise in a close-packed body-centred cubic structure and have a density of about 14.7 g/cm3, decreasing to 14.0 g/cm3 on melting, which is similar to that of mercury (13.534 g/cm3).

The small radius of the aluminium ion combined with its high charge make it a strongly polarizing species, prone to covalency.

[n 13] At lower temperatures, aluminium increases its deformation strength (as do most materials) whilst maintaining ductility (as do face-centred cubic metals generally).

[114] It has a close-packed crystalline structure (BCN 6+6) but an abnormally large interatomic distance that has been attributed to partial ionisation of the thallium atoms.

[128] Tin is a soft, exceptionally[129] weak metal (MH 1.5);[n 15] a 1-cm thick rod will bend easily under mild finger pressure.

[143] Flerovium is expected to be a liquid metal due to spin-orbit coupling "tearing" apart the 7p subshell, so that its 7s27p1/22 valence configuration forms a quasi-closed shell similar to those of mercury and copernicium.

This increased reactivity is consistent with the quasi-closed shell of flerovium and the beginning of a new series of elements with the filling of the loosely bound 7p3/2 subshell, and is rather different from the relative nobility of bismuth.

Tellurium forms covalent bonds with most other elements, noting it has an extensive organometallic chemistry and that many tellurides can be regarded as metallic alloys.

[160] It has a simple cubic crystalline structure characterised (as determined by electron density calculations) by partially directional bonding,[161] and a BCN of 6.

[187] Tennessine, despite being in the halogen column of the periodic table, is expected to go even further towards metallicity than astatine due to its small electron affinity.

The hybrid metals As, Sb, Bi, Te, Po, At — which other authors would call metalloids — partake about equally the properties of both.

The nine chemically weak metals identified by them are beryllium, magnesium, aluminium, gallium, tin, lead, antimony, bismuth, and polonium.

Cardarelli,[203] writing in 2008, categorizes zinc, cadmium, mercury, gallium, indium, thallium, tin, lead, antimony and bismuth as fusible metals.

Britton, Abbatiello and Robins[206] speak of 'the soft, low melting point, heavy metals in columns lIB, IlIA, IVA, and VA of the periodic table, namely Zn, Cd, Hg; Al, Ga, In, Tl; [Si], Ge, Sn, Pb; and Bi.

They are ductile elements but, compared to their metallic periodic table neighbours to the left, have lower melting points, relatively low electrical and thermal conductivities, and show distortions from close-packed forms.

[214] Gray[215] identifies as ordinary metals: aluminium, gallium, indium, thallium, nihonium, tin, lead, flerovium, bismuth, moscovium, and livermorium.

[223] Farrell and Van Sicien[224] use the term poor metal, for simplicity, 'to denote one with a significant covalent, or directional character.'

Periodic table extract showing the location of the post-transition metals. Zn , Cd and Hg are sometimes counted as post-transition metals rather than as transition metals . The dashed line is the traditional dividing line between metals and nonmetals . The symbols for the elements commonly recognized as metalloids are in italics. The status of elements 110 to 118 has not been confirmed, though elements 113-116 are sometimes considered post-transition metals.
^ Aluminium is occasionally not counted as a post-transition metal given its absence of d electrons
† Polonium is sometimes instead counted as a metalloid
‡ Astatine is widely regarded as either a nonmetal or less often as a metalloid but has been predicted to be a metal
Scatter plot of electronegativity values and melting points for metals (up to fermium, element 100) and some borderline elements (Ge, As, Se, Sb, Te, At). Elements categorised by some authors as post-transition metals are distinguished by their relatively high electronegativity values, and relatively low melting points (Pt is anomalous in this regard). High electronegativity corresponds to increasing nonmetallic character; [ 1 ] low melting temperature corresponds to weaker cohesive forces between atoms and reduced mechanical strength. [ 2 ] The geography of the plot broadly matches that of the periodic table. Starting from the bottom left, and proceeding clockwise, the alkali metals are followed by the heavier alkaline earth metals ; the rare earths and actinides (Sc, Y and the lanthanides being here treated as rare earths); transition metals with intermediate electronegativity values and melting points; the refractory metals ; the platinum group metals; and the coinage metals (the latter three categories are sub-categories of the broader category of transition metals occupying groups 3–12 of the periodic table). The increased electronegativity of Be and Mg and the higher melting point of Be distances these light alkaline earth metals from their heavier congeners. This separation extends to other differences in physical and chemical behaviour between the light and heavier alkaline earth metals. [ n 1 ]
Platinum crystals