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Hazardous Chemicals Handbook 2 Episode 2

Tham khảo tài liệu 'hazardous chemicals handbook 2 episode 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | METALS 29 Bromine is a dark red volatile liquid with a pungent odour. The vapour attacks the eyes and mucous membranes. It combines spontaneously and with deflagration with phosphorus arsenic and potassium and with many other elements when warmed. It bleaches litmus and turns starch paper orange yellow. Iodine is a dark grey solid which is easily vaporized to a deep blue violet vapour. It is sparing soluble in water but dissolves in aqueous potassium iodide to give a brown solution. It combines directly with many elements. Metals A metal is an electropositive element. There are over 70 metals in the earth s crust. Examples include copper gold iron platinum silver and tungsten. Chemically in solution a metal atom releases an electron to become a positive ion. In bulk metals are solids and tend to have high melting and boiling points an exception is mercury . They are lustrous relatively dense malleable ductile cohesive and highly conductive to both electricity and heat. Metals are crystalline in structure and the individual crystals contain positive metal ions. The outer valency electrons appear to be so loosely held that they are largely interspersed amongst the positive ions forming an electron cloud which holds the positive ions together. The mobility of this electron cloud accounts for the electrical conductivity. The crystal structure also explains the hardness and mechanical strength of metals whereas the elasticity is explained by the ability of the atoms and ions to slide easily over each other. Metals can be blended with other metals to produce alloys with specific properties and applications. Examples include Brass alloy of copper and zinc used for ship s propellers screws wind instruments. Bronze alloy of copper and tin used for coins medals statues church bells. Duralumin alloy of aluminium magnesium copper and manganese used for structural purposes e.g. in aircraft construction. Nichrome alloy of nickel iron and chromium used for heating elements. .