Science / Periodic Table of Elements / Boron (B): Atomic number: 5, Atomic mass: 10.81 g.mol -1, Electronegativity: 2.0, Density: 2.3 g.cm-3 at 20°C, Melting point: 2076 °C, Boiling point: 3927 °C, Vanderwaals radius: 0.098 nm, Ionic radius: 0.027 nm, Isotopes: 2, Electronic shell: [ He ] 2s22p1, Energy of first ionisation: 800.5 kJ.mol -1, Energy of second ionisation: 2426.5 kJ.mol -1, Energy of third ionisation: 3658.7 kJ.mol -1, Discovered by: Sir Humphry Davy and J.L Gay-Lussac in 1808. Boron is a non metallic element and the only non-metal of the group 13 of the periodic table the elements. Boron is electron-deficient, possessing a vacant p-orbital. It has several forms, the most common of which is amorphous boron, a dark powder, unreactive to oxygen, water, acids and alkalis. It reacts with metals to form borides. At standard temperatures boron is a poor electrical conductor but is a good conductor at high temperatures. Applications: The most economically important compound of boron is sodium tetraborate decahydrate Na2B4O7 ?· 10H2O, or borax, used for insulating fiberglass and sodium perborate bleach. Boric acid is an important compound used in textile products. Compounds of boron are used in organic synthesis, in the manufacture of a particular type of glasses, and as wood preservatives. Boron filaments are used for advanced aerospace structures, due to their high-strength and light weight. An early use of borax was to make perborate, the beaching agent once widely used in household detergents. Boron compound also came into the average home in the guise of food preservatives, expecialy for margarine and fish. Boron in the environment: Boron is not present in nature in elemental form. It is found combined in borax, boric acid, kernite, ulexite, colemanite and borates. Vulcanic spring waters sometime contains boric acids. Borates are mined in US, Tibet, Chile and Turkey, with world production being about 2 million tonnes per year.
Health / Health Insurance / Section 1915(B) Waivers: Waivers that states could obtain from the federal government that allowed them to restrict a Medicaid beneficiary's choice of providers by using a primary care case manager or other arrangement. MORE
Entertainment / Photography / Bulb (B): Letter on the shutter dial indicating that the shutter will stay open while the release is depressed. MORE