page_title: Compounds of aluminium
hierarchical_section_title: Compounds of aluminium
caption_attribution_description: English: Bar of (Al) aluminium crystal growth raw material, with visible dendrites on the macroetched surface, purity 99.9998%, sector size about 55&#160;×&#160;37&#160;mm (from the collection of Ethan Currens). Français&#160;: Une barre d'Aluminium (Al), avec une surface dépolie à l'acide pour en révéler la structure. Pureté: 99,9998&#160;%, taille de la portion photographiée&#160;: 55&#160;×&#160;37&#160;mm environ. Deutsch: Sichtbare Strukturen auf der Oberfläche eines geätzten (Al) Aluminium-Barrens, Reinheit 99,9998&#160;%, Ausschnittsgröße ca. 55&#160;×&#160;37&#160;mm. Ελληνικά: (Al) ράβδος αλουμινίου, ορατές δομές σε μια χαραγμένη επιφάνεια, καθαρότητα 99.9998&#160;%, μέγεθος τομέα για 55 Γ&#160;? 37 χιλ. Italiano: Dettaglio superficiale (55&#160;×&#160;37&#160;mm) di una barra di alluminio (purezza ≥ 99,9998%). La superficie è stata pulita mediante attacco chimico con acido (etching o mordenzatura) in modo da evidenziare, anche a occhio nudo, la struttura dei cristalliti metallici.
context_page_description: Aluminium combines characteristics of pre- and post-transition metals. Since it has few available electrons for metallic bonding, like its heavier group 13 congeners, it has the characteristic physical properties of a post-transition metal, with longer-than-expected interatomic distances. Furthermore, as Al³⁺ is a small and highly charged cation, it is strongly polarizing and aluminium compounds tend towards covalency; this behaviour is similar to that of beryllium, an example of a diagonal relationship. However, unlike all other post-transition metals, the underlying core under aluminium's valence shell is that of the preceding noble gas, whereas for gallium and indium it is that of the preceding noble gas plus a filled d-subshell, and for thallium and nihonium it is that of the preceding noble gas plus filled d- and f-subshells. Hence, aluminium does not suffer the effects of incomplete shielding of valence electrons by inner electrons from the nucleus that its heavier congeners do.
context_section_description: Aluminium (or aluminum) combines characteristics of pre- and post-transition metals. Since it has few available electrons for metallic bonding, like its heavier group 13 congeners, it has the characteristic physical properties of a post-transition metal, with longer-than-expected interatomic distances. Furthermore, as Al³⁺ is a small and highly charged cation, it is strongly polarizing and aluminium compounds tend towards covalency; this behaviour is similar to that of beryllium (Be²⁺), an example of a diagonal relationship. However, unlike all other post-transition metals, the underlying core under aluminium's valence shell is that of the preceding noble gas, whereas for gallium and indium it is that of the preceding noble gas plus a filled d-subshell, and for thallium and nihonium it is that of the preceding noble gas plus filled d- and f-subshells. Hence, aluminium does not suffer the effects of incomplete shielding of valence electrons by inner electrons from the nucleus that its heavier congeners do. Aluminium's electropositive behavior, high affinity for oxygen, and highly negative standard electrode potential are all more similar to those of scandium, yttrium, lanthanum, and actinium, which have ds² configurations of three valence electrons outside a noble gas core: aluminium is the most electropositive metal in its group. Aluminium also bears minor similarities to the metalloid boron in the same group; AlX₃ compounds are valence isoelectronic to BX₃ compounds (they have the same valence electronic structure), and both behave as Lewis acids and readily from adducts. Additionally, one of the main motifs of boron chemistry is regular icosahedral structures, and aluminium forms an important part of many icosahedral quasicrystal alloys, including the Al–Zn–Mg class.
caption: Etched surface from a high purity (99.9998%) aluminium bar, size 55×37 mm
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