Kids Research Express

Compound,  in chemistry, a substance composed of  atoms  of two or more  elements  in chemical combination, occurring in a fixed, definite proportion and arranged in a fixed, definite structure. A compound is often represented by its chemical formula. The formula for water is H 2 O, and for sodium chloride, NaCl. The formula weight of a compound can be determined from its formula. The molecular weight of a molecular compound can be determined from its molecular formula. Two or more distinct compounds that have the same molecular formula but different properties are called isomers. Formation and Decomposition of Compounds Compounds are formed from simpler substances by  chemical reaction . Some compounds can be formed directly from their constituent elements, e.g., water from hydrogen and oxygen: 2H 2  + O 2  → 2H 2 O. Other compounds are formed by reaction of an element with another compound; e.g., sodium hydroxide (NaOH) is formed (and hydrogen gas released) by the reaction

Synthetic elements,  in chemistry, radioactive elements that were not discovered occurring in nature but as artificially produced isotopes. They are  technetium  (at. no. 43), which was the first element to be synthesized,  promethium  (at. no. 61),  astatine  (at. no. 85),  francium  (at. no. 87), and the  transuranium elements  (at. no. 93 and beyond in the  periodic table ). Some of these elements have since been shown to exist in minute amounts in nature, usually as short-lived members of natural radioactive decay series (see  radioactivity ). The synthetic elements through at. no. 100 ( fermium ) are created by bombarding a heavy element, such as uranium or plutonium, with neutrons or alpha particles. The synthesis of the transfermium elements (elements with at. no. 101 or greater) is accomplished by the fusion of the nuclei of two lighter elements. Elements 101 through 106 were first produced by fusing the nuclei of slightly lighter elements, such as  californium , with those

Ununhexium, artificially produced radioactive chemical element ; symbol Uuh; at. no. 116; mass number of most stable isotope 292; m.p., b.p., sp. gr., and valence unknown. Situated in Group 16 of the periodic table, it is expected to have properties similar to those of polonium and tellurium . In 1999 a research team at the Lawrence Berkeley National Laboratory in Calif. bombarded lead-208 atoms with high-energy krypton-86 ions to create, apparently, ununoctium (element 118) atoms. The Uuo-293 isotope that they synthesized emitted an alpha particle to decay into Uuh-289, which has a life-life of about 0.6 millisecond, which then emitted an alpha particle to decay into ununquadium (element 114). Although the Berkeley laboratory retracted its claim for creating ununoctium in 2001, other research teams have since created ununhexium directly. No name has yet been adopted for element 116, which is therefore called ununhexium, from the Latin roots un for one and hex for six, under a con

Ununoctium (y'nənŏk`tēəm), artificially produced radioactive chemical element ; symbol Uuo; at. no. 118. Scientists from the Joint Institute for Nuclear Research in Dubna, Russia, and Lawrence Livermore National Laboratory in California collaborated in the discovery of ununoctium in experiments conducted in 2002 and 2005. They bombarded atoms of californium -249  with ions of calcium -48. Among the products of the bombardments were three atoms of ununoctium-294 (one atom in 2002 and two in 2005), each of which decayed in 0.9 milliseconds into an atom of ununhexium by emitting an alpha particle . No name has yet been adopted for element 118, which is therefore called ununoctium, from the Latin roots un for one and oct for eight, under a convention for neutral temporary names proposed by the International Union of Pure and Applied Chemistry (IUPAC) in 1980. In 1999 a research team at the Lawrence Berkeley National Laboratory in Calif. bombarded lead-208 atoms with high-energy k

Element Symbol Atomic Number Atomic Weight 1 Melting Point (Degrees Celsius) Boiling Point (Degrees Celsius) actinium Ac 89 227.0278 1050. 3200. ±300 aluminum Al 13 26.98154 660.37 2467. americium Am 95 (243) 1172. 2600. antimony Sb 51 121.75 630.74 1750. argon Ar 18 39.948 −189.2 −185.7 arsenic As 33 74.9216 817. (at 28 atmospheres) 613. (sublimates) astatine At 85 (210) 302. (est.) 337. (est.) barium Ba 56 137.33 725. 1640. berkelium Bk 97 (247) 1050. 2590. beryllium Be 4 9.01218 1278. ±5 2970. bismuth Bi 83 208.9804 271.3 1560. ±5 bohrium Bh 107 (262) — — boron B 5 10.81 2300. 2550. (sublimates) bromine Br 35 79.904 −7.2 58.78 cadmium Cd 48 112.41 320.9 765. calcium Ca 20 40.08 839. ±2 1484. californium Cf 98 (251) 900. 1470. carbon C 6 12.011 ∼3550. 4827. cerium Ce 58 140.12 799. 3426. cesium Cs 55 132.9054 28.40 669.3 chlorine Cl 17 35.453 −100.98 −34.6 chromium Cr 24 51.996 1857. ±20 2672. cobalt Co 27 58.9332 1495. 2870. copper Cu 29 63.546 1083.4 ±0.2

Element, in chemistry, a substance that cannot be decomposed into simpler substances by chemical means. A substance such as a compound can be decomposed into its constituent elements by means of a chemical reaction, but no further simplification can be achieved. An element can, however, be decomposed into simpler substances, such as protons and neutrons or various combinations of them, by the methods of particle physics, e.g., by bombardment of the nucleus. The Atom The smallest unit of a chemical element that has the properties of that element is called an atom . Many elements (e.g., helium) occur as single atoms. Other elements occur as molecules made up of more than one atom. Elements that ordinarily occur as diatomic molecules include hydrogen, nitrogen, oxygen, and the halogens, but oxygen also occurs as a triatomic form called ozone. Phosphorus usually occurs as a tetratomic molecule, and crystalline sulfur occurs as molecules containing eight atoms. Atomic Number a

Mass number, often represented by the symbol A, the total number of nucleons (neutrons and protons) in the nucleus of an atom . All atoms of a chemical element have the same atomic number (number of protons in the nucleus) but may have different mass numbers (from having different numbers of neutrons in the nucleus). Atoms of an element with the same mass number make up an isotope of the element. Different isotopes of the same element cannot have the same mass number, but isotopes of different elements often do have the same mass number, e.g., carbon-14 (6 protons and 8 neutrons) and nitrogen-14 (7 protons and 7 neutrons).