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Periodic Properties: Groups I and II Group I—The Alkali Metals Elements and Symbols Ion. Energy(kJ/mol) 2 nd Ion. En. Li = Lithium 520 7300 Na = Sodium 495 4560 K = Potassium 419 3052 Rb = Rubidium 403 2633 Cs = Cesium 376 2230 Reactivity with water
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Periodic Properties: Groups I and II • Group I—The Alkali Metals • Elements and Symbols Ion. Energy(kJ/mol) 2nd Ion. En. • Li = Lithium 520 7300 • Na = Sodium 495 4560 • K = Potassium 419 3052 • Rb = Rubidium 403 2633 • Cs = Cesium 376 2230 • Reactivity with water • These elements need to lose 1 e- to be like a Noble Gas • Losing electrons is called “oxidation” • Water can gain electrons (“reduction”) • 2 M0(s) + 2 H2O(l) ------> 2 MOH(aq) + H2(g) • Example: 2 Na0(s) + 2 H2O(l) ------> 2 NaOH(aq) + H2(g) • Reactions are violently exothermic • Basic solutions are formed
Reactions with Oxygen • 4Li + O2 2Li2O Lithium Oxide [O2- is called oxide;] • 2Na + O2 Na2O2 Sodium Peroxide [O22- is called peroxide] • K + O2 KO2Potassium Superoxide [O2- is called superoxide] • Rb + O2 RbO2Rubidium Superoxide • Cs + O2 CsO2Cesium Superoxide B. Group II—The Alkaline Earth Metals • Elements and Symbols Ion. Energy(kJ/mol) 2nd Ion. En. • Be = Beryllium 900 1757 • Mg = Magnesium 738 1450 • Ca = Calcium 590 1145 • Sr = Strontium 550 1064 • Ba = Barium 503 965 • Reactions with Oxygen • Much more predictable: 2 M0(s) + O2(g) ------> 2 MO(s) • 2 Ca0(s) + O2(g) ------> 2 CaO(s)
3. Reactivity with water • These elements need to lose 2 e- to be like a Noble Gas • M0(s) + 2 H2O(l) ------> M(OH)2(aq) + H2(g) • Example: Mg0(s) + 2 H2O(l) ------> Mg(OH)2(aq) + H2(g) • Reactions are slow, with some bubbling visible • Basic solutions are formed 4. Reactivity with Acid a. M0(s) + 2 HCl(aq) ------> 2 MCl2(aq) + H2(g) • Mg0(s) + 2 HCl(aq) ------> 2 MgCl2(aq) + H2(g) • Ionization Energy • The energy required to remove an e- from a gaseous element • X(g) + I.E. ------> X+(g) + e- • More reactive metals have lower Ionization Energies • Ionization Energy decreases down a Group—the electron being removed is farther from the nucleus, thus easier to remove • Ca (I.E. = 590 kJ/mol) is more reactive than Mg (I.E. = 738 kJ/mol) • K (I.E. = 419 kJ/mol) is more reactive than Li (I.E. = 520 kJ/mol)
Calcium Metal Reacting with Water to Form Bubbles of Hydrogen Gas
Metal Oxides and Water • The Alkali and Alkaline Earth Metals react with water to make it basic • 2 Na0(s) + 2 H2O(l) ------> 2 NaOH(aq) + H2(g) • Mg0(s) + 2 H2O(l) ------> Mg(OH)2(aq) + H2(g) • The oxides of these metals also react with water to make basic solutions • 2KO2(s) + 2H2O(l) ------> 2KOH(aq) + O2(g) + H2O2(aq) • MgO(s) + H2O(l) ------> Mg(OH)2(aq) E. Notes on Today’s Lab • Do the reactions in the hood: H2 is produced • Do Part A first (metal hardness); then use same piece for Part B (H2O rxn) DON’T THROW METALS IN TRASH: THEY CAN CATCH ON FIRE 2 M0(s) + 2 ROH(l) ------> 2 M+OR-(aq) + H2(g) • Use the Bunsen burner in the hood to burn the Magnesium • Phenolpthalein is red under basic conditions • Orange pH paper turns blue under basic conditions