<P> Zinc and cadmium are electropositive while mercury is not . As a result, zinc and cadmium metal are good reducing agents . The elements of group 12 have an oxidation state of + 2 in which the ions have the rather stable d electronic configuration, with a full sub-shell . However, mercury can easily be reduced to the + 1 oxidation state; usually, as in the ion Hg, two mercury (I) ions come together to form a metal - metal bond and a diamagnetic species . Cadmium can also form species such as (Cd Cl) in which the metal's oxidation state is + 1 . Just as with mercury, the formation of a metal - metal bond results in a diamagnetic compound in which there are no unpaired electrons; thus, making the species very reactive . Zinc (I) is known only in the gas phase, in such compounds as linear Zn Cl, analogous to calomel . </P> <P> The elements in group 12 are usually considered to be d - block elements, but not transition elements as the d - shell is full . Some authors classify these elements as main - group elements because the valence electrons are in ns orbitals . Nevertheless, they share many characteristics with the neighboring group 11 elements on the periodic table, which are almost universally considered to be transition elements . For example, zinc shares many characteristics with the neighboring transition metal, copper . Zinc complexes merit inclusion in the Irving - Williams series as zinc forms many complexes with the same stoichiometry as complexes of copper (II), albeit with smaller stability constants . There is little similarity between cadmium and silver as compounds of silver (II) are rare and those that do exist are very strong oxidizing agents . Likewise the common oxidation state for gold is + 3, which precludes there being much common chemistry between mercury and gold, though there are similarities between mercury (I) and gold (I) such as the formation of linear dicyano complexes, (M (CN)). According to IUPAC's definition of transition metal as an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell, zinc and cadmium are not transition metals, while mercury is . This is because only mercury is known to have a compound where its oxidation state is higher than + 2, in mercury (IV) fluoride (though its existence is disputed, as later experiments trying to confirm its synthesis could not find evidence of HgF). However, this classification is based on one highly atypical compound seen at non-equilibrium conditions and is at odds to mercury's more typical chemistry, and Jensen has suggested that it would be better to regard mercury as not being a transition metal . </P> <P> Although group 12 lies in the d - block of the modern 18 - column periodic table, the d electrons of zinc, cadmium, and (almost always) mercury behave as core electrons and do not take part in bonding . This behavior is similar to that of the main - group elements, but is in stark contrast to that of the neighboring group 11 elements (copper, silver, and gold), which also have filled d - subshells in their ground - state electron configuration but behave chemically as transition metals . For example, the bonding in chromium (II) sulfide (CrS) involves mainly the 3d electrons; that in iron (II) sulfide (FeS) involves both the 3d and 4s electrons; but that of zinc sulfide (ZnS) involves only the 4s electrons and the 3d electrons behave as core electrons . Indeed, useful comparison can be made between their properties and the first two members of group 2, beryllium and magnesium, and in earlier short - form periodic table layouts, this relationship is illustrated more clearly . For instance, zinc and cadmium are similar to beryllium and magnesium in their atomic radii, ionic radii, electronegativities, and also in the structure of their binary compounds and their ability to form complex ions with many nitrogen and oxygen ligands, such as complex hydrides and amines . However, beryllium and magnesium are small atoms, unlike the heavier alkaline earth metals and like the group 12 elements (which have a greater nuclear charge but the same number of valence electrons), and the periodic trends down group 2 from beryllium to radium (similar to that of the alkali metals) are not as smooth when going down from beryllium to mercury (which is more similar to that of the p - block main groups) due to the d - block and lanthanide contractions . It is also the d - block and lanthanide contractions that give mercury many of its distinctive properties . </P> <Table> Comparison of the properties of the alkaline earth metals and the group 12 elements <Tr> <Th> Name </Th> <Th> Beryllium </Th> <Th> Magnesium </Th> <Th> Calcium </Th> <Th> Strontium </Th> <Th> Barium </Th> <Th> Radium </Th> </Tr> <Tr> <Td> Valence electron configuration </Td> <Td> 2s </Td> <Td> 3s </Td> <Td> 4s </Td> <Td> 5s </Td> <Td> 6s </Td> <Td> 7s </Td> </Tr> <Tr> <Td> Core electron configuration </Td> <Td> (He) </Td> <Td> (Ne) </Td> <Td> (Ar) </Td> <Td> (Kr) </Td> <Td> (Xe) </Td> <Td> (Rn) </Td> </Tr> <Tr> <Td> Oxidation states </Td> <Td> + 2, + 1 </Td> <Td> + 2, + 1 </Td> <Td> + 2, + 1 </Td> <Td> + 2, + 1 </Td> <Td> + 2 </Td> <Td> + 2 </Td> </Tr> <Tr> <Td> Melting point </Td> <Td> 1560 K (1287 ° C) </Td> <Td> 923 K (650 ° C) </Td> <Td> 1115 K (842 ° C) </Td> <Td> 1050 K (777 ° C) </Td> <Td> 1000 K (727 ° C) </Td> <Td> 973 K (700 ° C) </Td> </Tr> <Tr> <Td> Boiling point </Td> <Td> 2742 K (2469 ° C) </Td> <Td> 1363 K (1090 ° C) </Td> <Td> 1757 K (1484 ° C) </Td> <Td> 1655 K (1382 ° C) </Td> <Td> 2170 K (1897 ° C) </Td> <Td> 2010 K (1737 ° C) </Td> </Tr> <Tr> <Td> Appearance </Td> <Td> white - gray metallic </Td> <Td> shiny gray metallic </Td> <Td> dull silver - gray </Td> <Td> silvery white metallic </Td> <Td> silvery gray </Td> <Td> silvery white metallic </Td> </Tr> <Tr> <Td> Density </Td> <Td> 1.85 g cm </Td> <Td> 1.738 g cm </Td> <Td> 1.55 g cm </Td> <Td> 2.64 g cm </Td> <Td> 3.51 g cm </Td> <Td> 5.5 g cm </Td> </Tr> <Tr> <Td> Pauling electronegativity </Td> <Td> 1.57 </Td> <Td> 1.31 </Td> <Td> 1.00 </Td> <Td> 0.95 </Td> <Td> 0.89 </Td> <Td> 0.9 </Td> </Tr> <Tr> <Td> Atomic radius </Td> <Td> 105 pm </Td> <Td> 150 pm </Td> <Td> 180 pm </Td> <Td> 200 pm </Td> <Td> 215 pm </Td> <Td> 215 pm </Td> </Tr> <Tr> <Td> Crystal ionic radius </Td> <Td> 59 pm </Td> <Td> 86 pm </Td> <Td> 114 pm </Td> <Td> 132 pm </Td> <Td> 149 pm </Td> <Td> 162 pm </Td> </Tr> <Tr> <Td> Flame test color </Td> <Td> white </Td> <Td> brilliant white </Td> <Td> brick - red </Td> <Td> crimson </Td> <Td> apple green </Td> <Td> crimson red </Td> </Tr> <Tr> <Td> Organometallic chemistry </Td> <Td> good </Td> <Td> good </Td> <Td> poor </Td> <Td> very poor </Td> <Td> very poor </Td> <Td> extremely poor </Td> </Tr> <Tr> <Td> Hydroxide </Td> <Td> amphoteric </Td> <Td> basic </Td> <Td> basic </Td> <Td> strongly basic </Td> <Td> strongly basic </Td> <Td> strongly basic </Td> </Tr> <Tr> <Td> Oxide </Td> <Td> amphoteric </Td> <Td> strongly basic </Td> <Td> strongly basic </Td> <Td> strongly basic </Td> <Td> strongly basic </Td> <Td> strongly basic </Td> </Tr> <Tr> <Th> Name </Th> <Th> Beryllium </Th> <Th> Magnesium </Th> <Th> Zinc </Th> <Th> Cadmium </Th> <Th> Mercury </Th> <Th> Copernicium </Th> </Tr> <Tr> <Td> Valence electron configuration </Td> <Td> 2s </Td> <Td> 3s </Td> <Td> 4s </Td> <Td> 5s </Td> <Td> 6s </Td> <Td>? 7s </Td> </Tr> <Tr> <Td> Core electron configuration </Td> <Td> (He) </Td> <Td> (Ne) </Td> <Td> (Ar) 3d </Td> <Td> (Kr) 4d </Td> <Td> (Xe) 4f 5d </Td> <Td>? (Rn) 5f 6d </Td> </Tr> <Tr> <Td> Oxidation states </Td> <Td> + 2, + 1 </Td> <Td> + 2, + 1 </Td> <Td> + 2, + 1 </Td> <Td> + 2, + 1 </Td> <Td> + 4, + 2, + 1 </Td> <Td>? + 4, + 2, + 1, 0 </Td> </Tr> <Tr> <Td> Melting point </Td> <Td> 1560 K (1287 ° C) </Td> <Td> 923 K (650 ° C) </Td> <Td> 693 K (420 ° C) </Td> <Td> 594 K (321 ° C) </Td> <Td> 234 K (− 39 ° C) </Td> <Td>? </Td> </Tr> <Tr> <Td> Boiling point </Td> <Td> 2742 K (2469 ° C) </Td> <Td> 1363 K (1090 ° C) </Td> <Td> 1180 K (907 ° C) </Td> <Td> 1040 K (767 ° C) </Td> <Td> 630 K (357 ° C) </Td> <Td> 357 K (84 ° C) </Td> </Tr> <Tr> <Td> Appearance </Td> <Td> white - gray metallic </Td> <Td> shiny gray metallic </Td> <Td> silvery bluish - gray metallic </Td> <Td> silver - gray </Td> <Td> silvery </Td> <Td>? </Td> </Tr> <Tr> <Td> Density </Td> <Td> 1.85 g cm </Td> <Td> 1.738 g cm </Td> <Td> 7.14 g cm </Td> <Td> 8.65 g cm </Td> <Td> 13.534 g cm </Td> <Td>? 23.7 g cm </Td> </Tr> <Tr> <Td> Pauling electronegativity </Td> <Td> 1.57 </Td> <Td> 1.31 </Td> <Td> 1.65 </Td> <Td> 1.69 </Td> <Td> 2.00 </Td> <Td>? </Td> </Tr> <Tr> <Td> Atomic radius </Td> <Td> 105 pm </Td> <Td> 150 pm </Td> <Td> 135 pm </Td> <Td> 155 pm </Td> <Td> 150 pm </Td> <Td>? 147 pm </Td> </Tr> <Tr> <Td> Crystal ionic radius </Td> <Td> 59 pm </Td> <Td> 86 pm </Td> <Td> 88 pm </Td> <Td> 109 pm </Td> <Td> 116 pm </Td> <Td>? 75 pm </Td> </Tr> <Tr> <Td> Flame test color </Td> <Td> white </Td> <Td> brilliant white </Td> <Td> bluish - green </Td> <Td>? </Td> <Td>? </Td> <Td>? </Td> </Tr> <Tr> <Td> Organometallic chemistry </Td> <Td> good </Td> <Td> good </Td> <Td> good </Td> <Td> good </Td> <Td> good </Td> <Td>? </Td> </Tr> <Tr> <Td> Hydroxide </Td> <Td> amphoteric </Td> <Td> basic </Td> <Td> amphoteric </Td> <Td> weakly basic </Td> <Td>? </Td> <Td>? </Td> </Tr> <Tr> <Td> Oxide </Td> <Td> amphoteric </Td> <Td> strongly basic </Td> <Td> amphoteric </Td> <Td> mildly basic </Td> <Td> mildly basic </Td> <Td>? </Td> </Tr> </Table>

Which group on the periodic table contains magnesium