MOST is UNESCO’s intergovernmental science programme on MOST n.8 PDF transformations. MOST works with governments, social and human science communities and civil societies to improve connections between knowledge and action, connections that are one key to positive social change. Within the United Nations Sustainable Development Goals, MOST contributes to development and the eradication of poverty, as well as to the achievement of UNESCO’s Global Priorities: Africa and Gender Equality.
Författare: East Journal.
Test questions from the PISA 2018 Field Trial. These are examples of the test the 15-year-olds took for the PISA 2018 Field Trial. A script-enabled browser is required for this page to function properly. The next generation of Creative Cloud is here. Cutting-edge photography tools so you can easily edit, organize, store, and share from anywhere.
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Aluminium or aluminum is a chemical element with symbol Al and atomic number 13. It is a silvery-white, soft, nonmagnetic and ductile metal in the boron group. Aluminium is remarkable for its low density and its ability to resist corrosion through the phenomenon of passivation. Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals. Of aluminium isotopes, only one is stable: 27Al. This is consistent with the fact aluminium’s atomic number is odd. It is the only isotope that has existed on Earth in its current form since the creation of the planet.
The remaining isotopes of aluminium, with mass numbers ranging from 21 to 43, all have half-lives well under an hour. Three metastable states are known, all with half-lives under a minute. An aluminium atom has 13 electrons, arranged in an electron configuration of 3s23p1, with three electrons beyond a stable noble gas configuration. A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53. In highly acidic solutions, aluminium reacts with water to form hydrogen, and in highly alkaline ones to form aluminates— protective passivation under these conditions is negligible.
However, because of its general resistance to corrosion, aluminium is one of the few metals that retains silvery reflectance in finely powdered form, making it an important component of silver-colored paints. 3 H2 This conversion is of interest for the production of hydrogen. However, commercial application of this fact has challenges in circumventing the passivating oxide layer, which inhibits the reaction, and in storing the energy required to regenerate the aluminium metal. All four trihalides are well known.
Aluminium hydrolysis as a function of pH. Aluminium forms one stable oxide with the chemical formula Al2O3. It can be found in nature in the mineral corundum. Aluminium oxide is also commonly called alumina. The pale yellow crystals consist of tetrahedral aluminium centers. It reacts with water or dilute acids to give methane.