14 - Chemistry 1000 Lecture 14: The alkaline earth metals...

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Unformatted text preview: Chemistry 1000 Lecture 14: The alkaline earth metals Marc R. Roussel Group 2: The alkaline earth metals I Group 2, except maybe Be I Soft metals I Form M 2+ cations I Very negative reduction potentials: M 2+ (aq) + 2e- M (s) Element Be Mg Ca Sr Ba Ra E / V- 1 . 847- 2 . 356- 2 . 84- 2 . 89- 2 . 92- 2 . 92 I Chemistry often similar to alkali metals, but less reactive Example: Reaction with water: M (s) + 2H 2 O M(OH) 2 + H 2(g) = Often has to be done in hot water or with steam Why alkaline earth metals? The name alkaline earth was originally applied to the oxides of these metals. Earth is a term applied by early chemists to nonmetallic substances which are insoluble in water and remain stable when heated. The alkaline earth metal oxides have these properties. Alkaline means basic. The alkaline earth metal oxides, to the extent that they dissolve at all in water, make basic solutions: MO (s) + H 2 O (l) M(OH) 2 Ionic compounds I Alkaline earth metal compounds tend to be ionic, except for compounds of Be, which displays some peculiar chemistry. I Ionic compounds of the alkaline earth metals with monovalent anions (e.g. NO- 3 , Cl- ) tend to be soluble in water, except hydroxides and fluorides , which are at best slightly soluble. I Ionic compounds of the alkaline earth metals with divalent anions tend to be insoluble (MCO 3 , MSO 4 ) or only slightly soluble (MS) in water. Why MgCl 2 and not MgCl (revisited)? I The first ionization energy of magnesium is 737.7kJ/mol, while the second ionization energy is 1451kJ/mol. Why dont we see MgCl, which should be energetically easy to make? I Mg + would be a lot larger than Na + , perhaps similar in size to K + , so the lattice formation enthalpy of MgCl might be similar to that of KCl, which is- 717kJ / mol....
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This note was uploaded on 03/03/2012 for the course CHEM 1000 taught by Professor Marc during the Fall '06 term at Lethbridge College.

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14 - Chemistry 1000 Lecture 14: The alkaline earth metals...

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