Chapter_11_Notes

Chapter_11_Notes - Alkaline Earth Metals Be, Mg, Ca, Sr,...

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1 Alkaline Earth Metals Shriver, Chapter 11 Be, Mg, Ca, Sr, Ba, Ra Origins and Preparation Beryllium-named for the mineral beryl (Be 3 Al 2 (SiO 3 ) 6 ). - basis of the gem emerald (with color from Cr 3+ impurity) - extracted by heating beryl with sodium hexafluorosilicate to form BeF 2 , then reduction with Mg Magnesium- named for the Greek word for a district in Greece called Magnesia - 8 th most abundant element in the earth’s crust - occurs naturally in minerals dolomite and magnesite - 3 rd most abundant element in sea water - obtained by extraction in sea water (brine), followed by electrolysis of MgCl 2 CaO + H 2 O Ca 2+ + 2 OH - Mg 2+ + 2 OH - Mg(OH) 2 Mg(OH) 2 + 2 HCl MgC 2 + 2 H 2 O Mg 2+ cathode, reduced to Mg Cl - anode, oxidized to Cl 2 - can also be extracted from dolomite CaMg(CO 3 ) 2 + heat MgO + CaO + 2 CO 2 MgO + CaO + FeSi + heat CaSiO 4 + Fe + Mg - highly reactive toward oxygen and water, and can also react with N 2 (glovebox not as inert as you might hope!) 3 Mg + N 2 Mg 3 N 2 Calcium- name from Latin calx (lime) - 5 th most abundant element in earth’s crust - 7 th most abundant element in the ocean - found in biominerals: bone, shell, teeth - used in cell signaling - extracted by electrolysis of CaCl 2 (by-product in Solvay process) Strontium- named after Scottish village of Strontian (where it was first found) - extracted by electrolysis of SrCl2 or reduction of SrO with Al 6 SrO + 2 Al 3 Sr + Sr 3 Al 2 O 6
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2 Barium- named for Greek word for heavy - extracted by electrolysis of BaCl 2 or reduction of BaO with Al Radium- named for Latin radius (ray) - discovered in 1936 by Marie Curie and her husband Pierre from extraction of U from pitchblende (decay product of U) - all isotopes of Ra are radioactive (25 known) - 1 st radioactive element to be made synthetically - very rare Uses of the alkaline earths Be: moderator for nuclear reactors (high neutron capture cross-section) forms light alloys (usually with Cu) for aerospace industry X-ray transparent windows for X-ray absorption spectroscopy uses limited because it is exceedingly poisonous, especially if inhaled acute Be disease (severe chemical pneumonia), displaces Mg 2+ from enzymes chronic Be disease (berylliosis), triggers immune response Mg: essential element in plants (e.g., chlorophyll, ATP) also in humans: recommended daily intake 0.3 g (average human body contains 25 g Mg) milk of magnesia: Mg(OH) 2 (slightly basic) Epsom salts: MgSO 4 •7H 2 O the lightest construction metal (one-third less dense than Al) fireworks, flares Grignard reagents (alkylating agents) Ca: biominerals (CaCO 3 ), cell signaling and muscle cells CaCO 3 used in Solvay process for Na 2 CO 3 lime (CaO), used in making cement, steel and paper preparation: CaCO 3 CaO + CO 2 , at 900 °C CaO + aluminosilicate calcium silicate, calcium aluminate (cement) (lime mortar known to Romans) cement mixed with sand and water to make concrete gypsum (CaSO 4
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Chapter_11_Notes - Alkaline Earth Metals Be, Mg, Ca, Sr,...

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