Atomic Mass Unit

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Atomic mass unit or amu, in chemistry and physics, unit defined as exactly 1-12 the mass of an atom of carbon-12, the isotope of carbon with six protons and six neutrons in its nucleus. One amu is equal to approximately 1.66 × 10−24 grams.

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Beryllium

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. Beryllium, symbol Be, gray, brittle metallic element, with an atomic number of 4. It is in group 2 (or IIa) of the periodic table (see Periodic Law ). Beryllium was named for its chief mineral, beryl , an aluminum beryllium silicate. It was discovered as an oxide, now known as beryllia, in 1797 by French chemist Louis Nicolas Vauquelin. The free element was first isolated in 1828 independently by Friedrich Wöhler and Antonine Alexandre Brutus Bussy. Because the soluble compounds are sweet-tasting, the new element was first called glucinium, a reference to the sugar glucose . PROPERTIES AND OCCURRENCE Beryllium, one of the alkaline earth metals , ranks about 51st in natural abundance among the elements in the earth's crust. Its atomic weight is 9.012. Beryllium melts at about 1287° C (about 2349° F), boils at about 3000° C (about 5432° F), and has a specific gravity of 1.85. Beryllium has a high strength per unit weight. It tarnishes only slightly in air, becoming covered with a
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Electricity and Magnetism

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. Many similarities exist between electric and magnetic phenomena. A magnet has two opposite poles, referred to as north and south. Opposite magnetic poles attract each other, and similar magnetic poles repel each other, exactly as happens with electric charges. The force with which magnetic poles attract or repel each other depends on the strength of the poles and the distance between them. This relationship is similar to the Coulomb’s inverse square law for electric charges. See also Magnetism . The similarities between electric and magnetic phenomena indicate that electricity and magnetism are related. Electricity produces magnetic effects and magnetism produces electric effects. The relationship between electricity and magnetism is called electromagnetism. See also Quantum Electrodynamics . Magnetic Effects of Electricity It has been noted that an electric field exists around any electric charge. If electric charges are moving, they constitute an electric current. The magnetic eff
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Periodic Law

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. Periodic Law, in chemistry, law stating that many of the physical and chemical properties of the elements tend to recur in a systematic manner with increasing atomic number. Progressing from the lightest to the heaviest atoms, certain properties of the elements approximate those of precursors at regular intervals of 2, 8, 18, and 32. For example, the 2nd element (helium) is similar in its chemical behavior to the 10th (neon), as well as to the 18th (argon), the 36th (krypton), the 54th (xenon), and the 86th (radon). The chemical family called the halogens, composed of elements 9 (fluorine), 17 (chlorine), 35 (bromine), 53 (iodine), and 85 (astatine), is an extremely reactive family. See Periodic Table of Elements
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