#chemical element

• Actinide — A metallic and radioactive chemical element belonging to the actinide (or actinoid) series, a stabilized structural group of 15 heavy elements located in the periodic table from actinium (atomic number 89) to lawrencium (atomic number 103). All these elements belong to the 'f' block (5f series) of transition metals, characterized by high nuclear instability, high density, and electrochemical properties closely correlated with those of actinium.
• Actinium — A radioactive, silvery-white metallic chemical element with atomic number 89 and symbol Ac, which initiates the actinide series in the periodic table. Discovered in 1899 by André-Louis Debierne, actinium is extremely rare in the Earth's crust, occurring in trace amounts within uranium ores. Structurally, it crystallizes in a face-centered cubic system, is highly reactive, and emits an intense bluish glow in the dark due to the ionization of the surrounding air.
• Actinium — The original neological form, Latin spelling, and official international English name for the chemical element 'actiniu' (symbol Ac, atomic number 89). This structural term defines the heavy radioactive metal in the 'f' block of the periodic table, used within global scientific literature and IUPAC standards to describe the properties of isotopes involved in nuclear fission processes or advanced oncological medical research.
• Actinium variant — An archaic graphic form or transliteration used in 19th-century science textbooks for the chemical element actinium; a Latinized literary name designating substances or compounds with specific radiant structural properties. In modern terminology, the term has been completely replaced by internationally standardized forms.
• Aluminum — A chemical element with atomic number 13 and symbol Al; it is a silvery-white, lightweight metal in the boron group, remarkable for its low density, malleability, high electrical and thermal conductivity, and excellent corrosion resistance due to a protective oxide layer.
• Americium — A synthetic, highly radioactive chemical element of the actinide series, with atomic number 95 and symbol Am. This silver-colored structural transuranium metal, originally obtained by bombarding plutonium with neutrons, is utilized in precision industrial applications, such as household smoke detectors and alpha radiation sources for laboratory analyses.
• Americium — A variant graphical form or unadapted direct borrowing from English or Latin for the radioactive transuranium chemical element with atomic number 95, named in standard Romanian 'americiu'. It sometimes appears in imported technical papers, international databases, or commercial chemical catalogs to indicate the atomic structure Am of the actinide series.
• Arsenic — A chemical element with atomic number 33 and symbol As, located in group 15 of the periodic table, classified as a metalloid with properties intermediate between metals and non-metals. It occurs in several allotropic forms (the most stable being grey arsenic, with a metallic luster), is a semiconductor used in microelectronics and optoelectronics, and, in compound forms, is historically recognized as an extremely dangerous cellular toxin with severe industrial uses.
• Arsenic — The common name given to arsenic trioxide or the element arsenic itself, recognized as an inorganic crystalline mineral compound of extreme toxicity, historically used as a potent poison, but also in infinitesimal doses in medical or metallurgical processes. When used as an adjective, it describes a substance or an acid derived directly from arsenic, capable of forming salts called arsenates.
• Astatine — A highly unstable radioactive chemical element of the halogen group, with atomic number 85 and symbol At; it is the rarest naturally occurring element in the Earth's crust, produced only transiently through the decay of uranium and thorium, and due to its extremely short half-life (a maximum of 8.1 hours for its most stable isotope), its physical properties are studied almost exclusively through artificial synthesis techniques in particle accelerators.
• Astatine — An alternative, synonymous, and tolerated name within the scientific community for the chemical element 'astatin'; it follows the classical terminological pattern of metals and metalloids (with the suffix '-ium'), occasionally used in textbooks or older technical translations to denote the element with atomic number 85.
• Nitrogen — A gaseous chemical element, colorless, odorless, and tasteless, with atomic number 7 and symbol N, constituting approximately 78% of the Earth's atmosphere by volume; it is a fundamental component of amino acids, proteins, and nucleic acids, essential for all living organisms and widely used in industry in liquid form as a cryogenic agent or within chemical fertilizers.