Nucleus

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Nucleus (atomic structure), in atomic structure, the positively charged central mass of an atom about which the orbital electrons revolve. The nucleus is composed of nucleons, that is, protons and neutrons, and its mass accounts for nearly the entire mass of the atom.

See Elementary Particles; Neutron; Proton.

See also: Nuclear Energy; Electron

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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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Converting Food to Usable Energy

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Cellular respiration is a complex series of chemical reactions that harvests the energy trapped in the bonds of glucose sugar molecules and converts it into a chemical form that can be stored for later use. Humans and other animals obtain glucose sugar molecules from food, such as the fruits and grains shown here, while plants create glucose sugars in the process of photosynthesis. Essential to the survival of most organisms on Earth, cellular respiration yields the energy that makes our bodies function properly.
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