Ch 11. Group 1 (Alkali Metals)

2

Hvap (in kJ/mol) for Metals

3

Elemental Metals

Synthesis by electrolysis

2 KOH K (m) + ½ O2 (g) + H2O (l)

Sir Humphrey Davy, 1807 (K, Na)

Reactivities:

M (m) + H2O MOH (aq) + ½ H2 (g)

Li is rapid; Na to Cs is increasingly violent, explosive

4

Elemental properties

5

Pourbaix s-block

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Born-Haber approach

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Solution and lattice enthalpies

8

Exchange / Displacement Large ion salt + small ion salt is better than two salts with

large and small ions combined.

Example: Salt ΔHL sum

CsF 750

NaI 705 1455 kJ/mol

CsI 620

NaF 926 1546

This can help predict some reactions like displacements, ion exchange, thermal stability.

9

Crown ethers and cryptands

Formation constants with alkali metal cations

[M(OH2)n]+ + ether = [M(ether)]+ + n H2O Kf

10

Alkides, electrides2 Na(s) Na+ (solv) + Na- (solv)

Na+(solv) [Na(crypt)]+Na- (s) en = ethylenediammine, H2NCH2CH2NH2

en

N2

2,2,2 crypt

ΔHrxn = 2ΔHat(Na) + I(Na) – Ea(Na) + ΔHsolv, cation + ΔHsolv, anion

sodide anion

= 2(108) + 514 - 52 + ? + ?

? We know that ΔHhyd(Na+) = - 400 kJ/mol

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Electrides

[Cs(18-C-6)2]+e-

Cs(15-C-5)2 Cs+ is the green sphere, electride anion is pink

12

Li clusters

Ch 12. Group 2 (Alkaline Earths)

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Element properties

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Be compounds

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Organo Be compounds

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Organometallics synthesis

Hg(CH3)2 + Be (s) → Be(CH3)2 + Hg (l) transmetallation

BuLi + BeCl2 → Bu2Be + 2 LiCl (s) halogen exchange

BuCl + 2 Li(s) → BuLi + LiCl (s) lithiation

BuLi + C6H6 → LiC6H5 + C4H10

Mg(s) + RX → 2 RMgX insertion (Grignard) insertion

R2Be + 2 MgCl2(s)

BeCl2

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Thermal stability of metal carbonates

An important industrial reaction involves the thermolysis of metal carbonates to form metal oxides according to:

MCO3 (s) → MO (s) + CO2 (g) G must be negative for the reaction to proceed. At the lowest

reaction temp:

G = 0 and Tmin = H / S S is positive because gas is liberated. As T increases, G

becomes more negative (i.e. the reaction becomes more favorable). S depends mainly on S0{CO2(g)} and is almost independent of M.

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Thermal stability of metal carbonates

MCO3 (s) → MO (s) + CO2 (g)

Tmin almost directly proportional to H.

HL favors formation of the oxide (smaller anion) for smaller cations.

So Tmin for carbonates should increase with cation size.

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Carbonate stabilities

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Mg2+ chelation with EDTA

EDTA = ethylenediaminetetraacetate