An aluminium atom has 13 electrons, arranged in an electron configuration of [Ne]3s23p1, with three electrons beyond a stable noble gas configuration. Accordingly, the combined first three ionization energies of aluminium are far lower than the fourth ionization energy alone. Aluminium can relatively easily surrender its three outermost electrons in many chemical reactions. The electronegativity of aluminium is 1.61 (Pauling scale).
A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the ionic radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure, aluminium atoms (when not affected by atoms of other elements) form a face-centered cubic crystal system by metallic bonding provided by atoms' outermost electrons; hence, aluminium (at these conditions) is a metal. This crystal system is shared by some other metals, such as lead and copper; the size of a unit cell of aluminium is comparable to that of those other metals.
No elements with odd atomic numbers have more than two stable isotopes; even-numbered elements have multiple stable isotopes, with tin (element 50) having the highest number of stable isotopes of all elements, ten.
Al is essentially the only isotope representing the element on Earth, which makes aluminium a mononuclidic element and practically equates its standard atomic weight to that of the isotope. Such a low standard atomic weight of aluminium has effects on the properties of the element.
Most other metals have greater standard atomic weights: for instance, that of iron is 55.8; copper 63.5; lead 207.2.
26Al is produced from argon in the Earth's atmosphere by spallation from cosmic ray protons and used in radiodating. The ratio of 26Al to 10Be has been used to study transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales.
The energy released by the decay of 26Al may have been responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.
Al has a half-life of 7.17×105 y, β+ decay δ=1.17 to 26
Mg, electron capture (ε) to 26
Mg, or gamma radiation (γ) δ=1.8086.
- 27Al is the only stable isotope, 13 protons and 14 neutrons.
Al has 13 protons and 29 neutrons.
The aluminides are those naturally occurring minerals with a high atomic % aluminum.
In the image on the right of a flake of native aluminum, the scale bar = 1 mm.
"Aluminium is the third most abundant element (after oxygen and silicon) in the Earth's crust, and the most abundant metal there. It makes up about 8% by mass of the crust, though it is less common in the mantle below."
The image at the top of this lecture is one of two images exhibiting native aluminum.
This flake was discovered, "During a field trip to the NW Rila Mountain in the early 1960s, one of us (V.A.) investigated the desilicated pegmatite apophysis and, from the phlogopite zone (Fig. 1c), collected a rock specimen with a protruding metallic flake visible to the naked eye (Fig. 2) [from which the above image was cropped]."
The designation for native aluminum is Al0 as indicated in, "Here we present data for a unique Al0 flake protruding from the phlogopite matrix of a rock specimen collected from a desilicated pegmatite vein."
The second image of native aluminum is shown on the right of this section. The sample is from a mud volcano in the Caspian Sea near Baku, Azerbaidzhan.
The type locality for native aluminum is the Tolbachik volcano, Kamchatka, Russia.
Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments; instead, aluminum is found combined in over 270 different minerals.
"As Andean glaciers recede, there has been an increase in seasonal discharge and in catchments with the least glacierized area and a decrease in total annual discharge [...] Dry season examinations, including this study, are particularly important because during this period glacial melt provides up to 40% of the total discharge in the Cordillera Blanca (Mark et al., 2005). The dry season thus provides the greatest potential opportunity to evaluate water quality deterioration related to glacial retreat. [...] In the Cordillera Blanca, the exposure of fresh sulfide-rich lithologies by retreating glaciers (Wilson et al., 1967) is thus integral to the biogeochemistry of proglacial streams. [...] the dry season geochemistry of trace and minor elements was examined in the proglacial Rio Quilcay from within 1 km of its glacier origins to 12 km downstream."
The "Rio Quilcay [is] a glacial-fed tributary to the Upper Rio Santa in the uppermost 12 km at elevations ranging from approximately 4800 to ~3800 m.a.s.l. [...] The sampled region of the Rio Quilcay receives glacial melt directly and indirectly from two proglacial lakes: Cuchillacocha and Tulpacocha. Geology in this region of the Cordillera Blanca includes pyrite schists and phyllite and pyrite-bearing quartzite intruded by a central granodiorite-tonalite batholith all overlain by clastic sediments deposited during glacial retreat (Wilson et al., 1967). Sulfide-rich lithologies are prevalent especially in the north-eastern high-altitude regions of the Cordillera Blanca (e.g. the Rio Quilcay Valley) with fresh exposures resulting from glacial scour (Wilson et al., 1967). Many headwaters in the Cordillera Blanca, including the Rio Quilcay and its tributaries, have ochreous precipitates"
"Aluminum, Ca, Fe, K, Mn, Na, and Si were determined using an Optima 3000 DV Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) using five calibration standards that bracketed the range of concentrations within the samples, excepting the three highest samples which were diluted 1:10 before analyses. Cobalt, Cu, Ni, Pb and Zn were determined on a Perkin–Elmer Sciex Elan 6000Ⓡ Inductively Coupled Plasma-Mass Spectromenter (ICP-MS) also using five calibration standards, however with no sample dilution. All element results were drift corrected. Sulfate and NO3- were determined using a Dionex DX-120 ion chromatograph (IC). Only SO42- is reported because other anions fall near detections limits (DLs) in the higher elevation samples, or represent less than 5% of the charge balance in the pH < 4 streams."
It "is likely that both the sulfide-rich lithology underlying the Rio Quilcay and the near-glacier sample locations enhanced sulfide weathering, and generated exceptionally high cation loads."
"Elevated dissolved Al, Fe and Cu concentrations (6.1mg/L, 21.4 mg/L, 6.1 lg/L) were observed at site 11, 0.3 km immediately downstream of a moraine. Concentrations of these elements increased by more than four times the concentrations at site 10. Concentration gains were likely associated with glacier melt rapidly weathering minerals within the moraine (Brown, 2002)."
"Tributary C also influenced the chemical composition of the stream immediately below its inflow at site 13. In fact, Fe reached the second highest concentration reported (12.8 mg/L) and dissolved Al, Mn, Co, Cu, Ni and Zn concentrations also increased above their upstream values. Tributary C overlays a region with enhanced sulfide mineral oxidation [image at the right]. Evidence for this includes a major cation: SO42- equivalent ratio of 1, and abundant algal mats covered with yellow and orange precipitates (Bigham et al., 1996). In addition, dissolved Al and Zn increased an additional 270% and 160% relative to site 13–14, respectively, and after the inflow of tributary D."
No known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals.
"The aluminium abundance was derived from the resonance line at 394.4nm, and Al is underabundant by ∼ −0.7 dex with respect to iron." "These abundances are the LTE values; no NLTE corrections, as prescribed by Baumüller and Gehren (1997) and Baumüller et al. (1998), have been applied. The prescribed NLTE corrections for Teff = 6500K, log g = 4.0, [Fe/H] = –3.0 are –0.11 ... for ... Al .... If we assume these values to apply for our lower-gravity star [CS 29497-030], then Al follows iron". The elemental abundance ratios for CS 29497-030 of aluminum are [Al/H] = -3.37, [Al/Fe] = -0.67.
Both Al I absorption lines at 394.401±8.5 and 396.152±6.5 have been measured for Sirius.
The oxides and sulfates are the most useful compounds of aluminium.
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