1. Alkali Metals C t tContent1.1 Occurrence1.2 Properties Group

I IA1.3 Synthesis1.4 Technical Applications1.5 Flame Colouration

3Li

I, IA resp.

C1.6 Solubility of the Salts1.7 Complexes with Crown Ethers1 8 Compounds Formed with Oxygen 19

11Na

1.8 Compounds Formed with Oxygen1.9 Salts of the Oxoacids1.10 Biological Aspects

19K37RbRb55Cs87

„Alkali metals“

87Fr

Slide 1Inorganic Chemistry IProf. Dr. T. Jüstel

„

1.1 OccurrenceAb dAbundanceLi: 2.0.10-3%, Na: 2.7%, K 2.4%, Rb: 9.0.10-3%, Cs: 3.10-4%

Lithium (lithos) LiAl[SiO3]2 Spodumene: chain silicateGreek: stone LiAl[Si2O5]2 Petalite: phyllosilicate

S di ( ) N Cl R k lSodium (neter) NaCl Rock saltEgypt.: soda NaNO3 Chile saltpetre

Na2SO4 Glauber’s saltNa[AlSi3O8] Albite

Potassium (potasse) KCl SylviteFrench: potash KMgCl3

.6H2O Carnallite

Rubidium (rubidus) Accompanies the other alkali metalsG k d dGreek: deep red

Caesium (caesius) Accompanies the other alkali metalsG k k bl C Al[SiO ] P ll

Slide 2Inorganic Chemistry IProf. Dr. T. Jüstel

Greek: sky blue CsAl[SiO3] Pollux

1.2 PropertiesAll M b f th G A Hi hl R ti M t l d E hibitAll Members of the Group Are Highly Reactive Metals and Exhibitan Oxidation State of +I

Li N K Rb CLi Na K Rb CsAtomic number 3 11 19 37 55Electronic [He] [Ne] [Ar] [Kr] [Xe]configuration 2s1 3s1 4s1 5s1 6s1configuration 2s1 3s1 4s1 5s1 6s1

Electronegativity 1.0 1.0 0.9 0.9 0.9Ionisation energy [eV] 5.4 5.1 4.3 4.2 3.9Ionic radius Me+ forIonic radius Me forCN 6 [pm] 90 116 152 166 181Melting point Tm [°C] 181 98 63 39 28Boiling point Tb [°C] 1347 883 759 688 668g p b [ ]Density [g/cm3] 0.53 0.97 0.86 1.53 1.87Flame colouring crimson red yellow pale violet red violet blue violet• Combustion of the metals leads to oxides, peroxides or superoxides, depending on the size

of the cation• Lithium forms Li3N together with N2• The alkaline character of the hydroxides increases with increasing atomic number

All lk li t l t lli i b d t d bi t l t t (CN 8)Slide 3Inorganic Chemistry I

Prof. Dr. T. Jüstel

• All alkali metals crystallise in a body-centred cubic crystal structure (CN 8)

1.3 Synthesisf S i C i i iBy Means of Fused-Salt Electrolysis or by Chemical Reduction via Extremely

Strong Reducing AgentsLithiumFused-salt electrolysis of LiCl/KCl (eutectic blend)Li+ + e- Li(l) (E0 = - 3.04 V Lithium possesses the most negative standard potential of all

elements)

SodiumFused-salt electrolysis of NaCl (Downs-cell) Cathode: Na+(dissolved) + e- Na(s)Anode: 2 Cl-(dissolved) Cl2(g) + 2 e-

PotassiumReduction of molten KCl with Na

Rubidium, CaesiumBy chemical reductionCs Cr O (s) + Zr(s) 2 Cs(g) + 2 ZrO (s) + Cr O (s)

Slide 4Inorganic Chemistry IProf. Dr. T. Jüstel

Cs2Cr2O7(s) + Zr(s) 2 Cs(g) + 2 ZrO2(s) + Cr2O3(s)

1.4 ApplicationLithiLithium• Li-salts are important reagents in medicine• 6Li2H and 6LiD serve as explosive core in fusion weapons

El t f ll t h d Pb Al d M• Element of alloys to harden Pb, Al and Mg• Li-ion batteries

SodiumSodium• Important reducing agent• Starting material for the synthesis of Na2O2, NaNH2, NaH, NaCN, Na/Pb…..• Cooling agent in fast breeder reactorsg g• Low and high pressure Na discharge

lamps (589.0 + 589.6 nm)

P t iPotassium• KCl, K2SO4 and KNO3 as fertilizer

CaesiumCaesium• Photoelectric effect photocell• 137Cs (t1/2 = 30 a) is a ß-radiator (512 keV)

radiation source in medicine

Slide 5Inorganic Chemistry IProf. Dr. T. Jüstel

1.5 Flame ColourationTh l E it ti f El t C L d t th E i i f Vi ibl Li ht dThermal Excitation of Electrons Can Lead to the Emission of Visible Light and Thus to a Coloured Flame

Element Colour of FlameElement Colour of FlameLi Crimson redNa Yellow K Pale violet np1

Rb Red violetCs Blue violetCa Brick red Sr Red

p

1Ene

rgy T -h

Sr RedBa Pale greenB Green Pb Pale blue

ns1

As Pale blue Sb Pale blueCd RedC G t bl

In case of alkali metals, the outer electron ns1 is thermally excited. Upon relaxation to the ground state a photon (h) is emitting which energyCu Green to blue

Y Redstate a photon (h) is emitting which energy corresponds to the difference between the first excited and the ground state.

Slide 6Inorganic Chemistry IProf. Dr. T. Jüstel

1.6 Solubility of the SaltsTh S l bilit f th Alk li M t l S lt I D d t th R ti f (K+)/ (A )The Solubility of the Alkali Metal Salts Is Dependent on the Ratio of r(K+)/r(A-)

Equilibrium reaction: LiI(s) + CsF(s) ⇌ LiF(s) + CsI(s)L tti th l [kJ/ l] 759 756 1047 608 H0 140 kJ/ lLattice enthalpy [kJ/mol] -759 -756 -1047 -608 H0 = -140 kJ/mol

Solubility of alkali metal fluorides and iodidesSolubility of alkali metal fluorides and iodides (rokt.(F-) = 119 pm, rokt.(I-) = 206 pm)

RbFKF

Poorly soluble salts of the larger alkalimetals (Me = K, Rb, Cs) are those composed

10

CsIRbIKI

LiI NaICsF

RbFKF

at 2

0°C

( , , ) pof big anions:

Perchlorate MeClO40 1

1CsI

NaF

bilit

y (m

ol/l)

4Tetraphenylborate Me[B(C6H5)4]Hexanitrocobaltate Me3[Co(NO2)6]

80 100 120 140 160 1800.01

0.1

LiFSol

ub

( ti ) ( ) i t h d l di ti

Slide 7Inorganic Chemistry IProf. Dr. T. Jüstel

r(cation) (pm) in octahedral coordination

1.7 Complexes with Crown EthersTh S l bilit f Alk li M t l S lt i O i S l t C N t bl B I dThe Solubility of Alkali Metal Salts in Organic Solvents Can Notably Be Increased Through the Addition of Complexing Agents Crown Ethers

Complex of potassium ionwith 18-crown-6

OO

O

OO O

O

O

with 18-crown-6

O OOO O

O

O

12-crown-4 15-crown-5 18-crown-6

• These cyclic polyethers form highly stable complexes with alkali metal cationsThese cyclic polyethers form highly stable complexes with alkali metal cations

• Alkali metal salts, such as KMnO4, dissolve in non-polar solvents, e.g. CHCl3(trichloromethane), as soon as small amounts of crown ether are added.

• Even elemental Na can be dissolved using 18-crown-6, whereby Na anions(!) are formed:2 Na(s) + C20H36O6(l) [Na(C20H36O6)]+Na-(s)

Slide 8Inorganic Chemistry IProf. Dr. T. Jüstel

1.8 Compounds Formed with OxygenTh W kl P l i i Alk li M t l C ti A Abl t St bili E LThe Weakly Polarising Alkali Metal Cations Are Able to Stabilise Even Large Anions, f.i. Oxygen. The Reaction Therewith Leads to the Formation of Peroxides and Superoxides, with the Exception of Lithium

Metal Product of reaction with O2 Magnetism ColourLi Li2O diamagnetic whiteNa Na2O2 diamagnetic whiteNa Na2O2 diamagnetic whiteK, Rb, Cs KO2, RbO2, CsO2 paramagnetic orange

All oxo compounds react violently with H2O under formation of hydroxides:p y 2 yLi2O(s) + H2O(l) 2 LiOH(s)Na2O2(s) + 2 H2O(l) 2 NaOH(s) + H2O2(l)2 KO2(s) + 2 H2O(l) 2 KOH(s) + H2O2(l) + O2(g)2 2 2 2 2

Reaction with CO2 leads to carbonates:Li2O(s) + CO2(g) Li2CO3(s)2 Na2O2(s) + 2 CO2(g) 2 Na2CO3(s) + O2(g)4 KO2(s) + 2 CO2(g) K2CO3(s) + 3 O2(g)K2CO3(s) + H2O(l) + CO2(g) 2 KHCO3(s)

O i CO O i i iSlide 9Inorganic Chemistry I

Prof. Dr. T. Jüstel

KO2 is used as CO2 and H2O absorber in diving gear

1.8 Compounds Formed with OxygenO id A F d U th R ti f S id With O OOzonides Are Formed Upon the Reaction of Superoxides With Ozone O3

Synthesis: 2 MeO2 + O3 2 MeO3 + O2 (Me = K, Rb, Cs)

Decomposition: 2 MeO3 2 MeO2 + O2 (Me = K, Rb, Cs)

The O3- anion possesses 19 valence electrons an is thus paramagnetic!

O. O. -

O O O O

The bond order of the O-O bond is 1.5

Slide 10Inorganic Chemistry IProf. Dr. T. Jüstel

1.9 Salts of the OxoacidsS lt f C b i A id (C b t d H d C b t )Salts of Carbonic Acid (Carbonates and Hydrogen Carbonates)Me2CO3 2 Li+(aq) + CO2(g) + H2O(l) 2 H+(aq) + Li2CO3(s) “insoluble”

Na2CO3 “soda”K CO “ t h”K2CO3 “potash”

MeHCO3 2 NaHCO3(s) Na2CO3(s) + H2O(l) + CO2(g) sherbet powder and baking soda

Salts of Phosphoric Acid (Phosphates, Hydrogen Phosph. and Dihydrogen Phosph.)Me3PO4 “alkaline salts”Me HPOMe2HPO4MeH2PO4 “acidic salts”

Salts of Nitric Acid (Nitrates)Salts of Nitric Acid (Nitrates)MeNO3 NaNO3 “Chile saltpetre”

KNO3 “saltpetre”

Salts of Sulphuric Acid (Sulphates and Hydrogen Sulphates)Me2SO4 Na2SO4

.10H2O “Glauber’s salt” laxativeMeHSO “acidic salts”

Slide 11Inorganic Chemistry IProf. Dr. T. Jüstel

MeHSO4 acidic salts

1.10 Biological Aspectsi iLithium

Treatment of mental illnesses (e.g. bipolar disorder) Li interferes with the metabolism in the human brain (hindrance of a enzymatic

2conversion whereby Mg2+ ions play a major role) Diagonal relationship Li/Mg

Sodium/Potassium• Maintenance of membrane potentials (~ 60 mV) vie concentration gradients of Na+ and K+

across the cell membranes signal line, renal function• Transport of ions takes place through ion channels

Na+ [mmol/l] K+ [mmol/l] Na+Na+[ ] [ ]

Red blood cells 11 92Blood plasma 160 10 Na+

Na+

Na+K+

K+K+

K+

K+K+

Rubidium, CaesiumAre of no known biological importance

Na+K+ K+

Na+

Slide 12Inorganic Chemistry IProf. Dr. T. Jüstel