Lecture8_AlkaliMetals_bandw

This explains the low abundance of li compared to na

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Unformatted text preview: half-lives. – This explains the low abundance of Li compared to Na and K • Lithium is predominantly created by spallation (fragmentation) of heavier nuclei in interstellar space or through fission of heavier nuclei. – Spallation is a break-up (fission) of heavy nuclides into lighter ones by cosmic rays (energetic and charged subatomic particles). • Potassium-40 is radioactive (K-capture) with t½ = 1.3 ×109 years: 40 19 • 40K • K + e− → 40 18 Ar +ν 223Fr is important for geological dating. (t½ = 21.8 min) is the only naturally occurring isotope of this radioactive element. CHMB31H3 The Chemistry of Group 1 6 Chemical properties • • • • • Oxidation number +1 Very reactive metals, strong reductants Handling precautions Reactivity increases going down the group Combine directly with many elements of PSE giving binary compounds (hydrides, oxides, sulfides, carbides, nitrides, halides, etc.) • React with water (Li slowly, Na vigorously, K ‘firely’ while Rb & Cs explosively) releasing H2 and giving hydroxides which are the strongest Brønsted bases • Many alkali metal compounds are important in every day life and both in industry and laboratory. CHMB31H3 The Chemistry of Group 1 7 Reduction potentials • Keep in mind: ∆G0 = -zFE0cell & E0H+/H = 0 V M (s) + H+ M+ (aq) + 1/2 H2 (g) (galvanic cell) M (s) + H+ (reduction potential for M) M+ (aq) + 1/2 H2 (g) • 1st half-reaction for reduction potential broken into the Born Haber cycle (this is specific for each element M): ∆G = -zFE0 ≈ ∆H M+ (aq) + eM+ (aq) • −∆Hhyd M+ (g) −∆H EI M (g) M (s) −∆Ha M (s) 2nd half-reaction for reduction potential and its thermodynamics (always the same regardless of your M): 1/2 H2 (g) H+ (aq)...
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