INORGANIC CHEMISTRY

Inorganic chemistry is the branch of chemistry concerned with the properties and behavior of

inorganic compounds

*inorganic compounds are considered to be of a mineral, not biological, origin.

The Groups IA Elements

Content

• Introduction to group IA elements, general physical properties, appearance melting point and electrical conductivities of group IA.

• General chemical properties of alkali metals, reactions of group IA elements with water and relative reactivities descending the group.

• Compounds of the group IA elements – hydroxides, oxides, halides, hydrides and carbonates

• Manufacturing of sodium by electrolysis and its industrial applications

Introduction

• The alkali metals – lithium, sodium, potassium, rubidium, cesium and francium

Natural occurrences

• In nature : mineral and rocks (not found free in nature – easily oxidized)

• Na and K – common ; others – quite rare

• RadioactivityFr - heaviest element in group - highly radioactive - form by particle emission from

actiniumK and Cs – natural radioactive isotope

Element Mineral Compound

Lithium, Li Petalite

Spodumene

LiAlSi4O10

LiAlSi4O10

Sodium, Na

6th most abundant in the earth crust

Caustic Soda

Rock salt

Saltpeter

Trona

Mirabilite

Albite

NaOH

NaCl

NaNO3

Na2CO3.NaHCO3.2H2O

Na2SO4.10H2O

NaAlSi3O8

Potassium

8th most abundant in the earth crust

Potash

Sylvite

Carnalite

Orthoclase

K2CO3

KCl

KCl.MgCl2.6H2O

KAlSi3O8

Rubidium, Rb Lepiodolite impurities

Cesium, Cs Pollucite

Lepiodolite impurities

CsAl4Si9O26.H2O

Table 1.1 Occurrence of Group IA elements

Physical properties

• Silvery • Soft : can be cut with knife ; but Li is harder

- Na – soft (cold butter)

- Cs – slightly golden and melts in hand

- K – squeezed like clay or dough• Metals are soft and relatively low melting point

Reason : - one valence electron, ns1

- distance between the nucleus and valence electron is far

- the attraction between them is relatively weak

- weak metallic bonding cause the crystal structure to be deformed or broken down easily.

• Low densities : lowest molar mass in their period and largest atomic radii.

- Li floats on lightweight household oils

Element Mp Bp Density, g/mL

Standard Reduction Potential (SRP), V

First Ionization energy, KJ/mol

Lithium 180.5 1347 0.534 -3.05 520

Sodium 97.8 881 0.971 -2.71 496

Potassium 63.2 766 0.862 -2.92 419

Rubidium 39.0 688 1.53 -2.92 403

Cesium 28.5 705 1.87 -2.92 377

• Good electrical and thermal properties• Solubility

- Salts with small anions are very soluble in water- Salts with large and complex anions ; eg silicates and

aluminosilicates are not very soluble in water

Chemical properties

• Lowest ionization energy : single electron in the outer shell easily to remove

• Li – highest first ionization energy

– most easily to oxidize

Reason :

- atomic radii increase down a group

- Li+ ion is so small

- the charge density (charge to radius ratio) and polarizing power of

the Li cation will very high

- the strength of interactions of the Li cation with the water molecules

in solution is stronger

- Li hydrated cations interact so strongly with water molecules ;

• Very powerful reducing agents, extremely reactive and react vigorously with water

• Metal surface tarnishes rapidly – exposed to air, cold water and even ice

• SRP (-2.7 to -3.0) – strong tendency to form cations, 1+ ion in solution- SRP are small (and negative)Reason : elements are easily oxidized by losing one valence electron- Li – smallest SRP – least tendency to be reduced/greatest tendency to oxidized

• Reactivity : Li<Na<K<Rb<Cs (increased down a group)• Enthalpy of hydration

- for the ions are high, especially Li+ ion due to its small ionic radius.

- decreases down a group : Li, Na, K hydrated ; Rb and Cs rare hydrated

• Can reduce O2, Cl2, NH3, and H2 to form oxides, amides and hydrides• Formed ionic compound

• Anomalous behaviours of lithium.

Lithium Other Group 1 Metals

Form normal oxide, Li2O Na and K forms peroxide, and K, Rb and Cs form superoxide

Form Lithium nitride, Li3N Do not form M3N

Forms stable compounds with small anions. For example, LiH is stable up to 900 0C

NaH decomposes at 350 0C

Forms less stable compounds with large anions. For example, LiOH decomposes to Li2O

MOH (M = Na, K, Rb, Cs) is very stable

Strong tendency to form covalent compounds

Less or tendency to form covalent compounds

Reaction with water

• General reaction :

2M + 2H2O 2MOH + H2

• Alkali metals reduced the hydrogen in water to form hydroxide and hydrogen gas

• Reactivity towards water

- Li – react readily with vigorous bubbling - released hydrogen gas

- Na – react rapidly to produce heat

- K – causes the H2 to burst into flames and heat released

- Rb and Cs – explosive in water• Relative reactivity : increase down the group• Alkali metal : kept under anhydrous nonpolar liquids eg : mineral oil

and paraffin to prevent air oxidation

Compounds of the elements

a) Oxides

Oxide Properties Reaction Uses

oxide ; M2O

[O]2-

Li2O

White crystals

Basic oxide

Preparation :

4Li + O2 Li2O

(Lithium Oxide)

(limited oxygen)

Reaction:

Li2O + H2O 2LiOH

Peroxide

M2O2

[O2]2-

Na2O2

Basic oxide Preparation :

2Na + O2 Na2O2

Reaction:

Na2O2 + H2O 2NaOH + H2O2

Superoxide

MO2

[O2]-

KO2

RbO2

CsO2

Basic oxide Preparation:

K + O2 KO2

Reaction:

2KO2 + 2H2O 2KOH + H2O2 + O2

Compounds of the elements

b) Hydroxides

Hydroxide Properties Reaction Uses

Metal hydroxide

-Strong base

-Basicity increases down a group-White crystalline solid-water soluble-Become liquid when expose to air; except LiOH

Preparation:

2Na + 2H2O 2NaOH + H2

or from

Oxides or

Peroxides or

Superoxides

Reaction:

NaOH + HCl NaCl + H2O

Breathing equipment

NaOH – soap, bleach, sodium phosphate, and others

KOH – liquid soap, detergents, electrolyte in storage batteries, KOH aq – remove CO2 and SO2 from air

Compounds of the elements

c) Halides

Halides Properties Reaction Uses

Alkali metal

-White crystalline solid-Thermally stable-Soluble in water except LiF-LiCl, LiBr and LiI : soluble in alcohol and less polar solvent, ethoxyethane

Preparation:

1. 2M + Cl2 2MCl

2. NaOH + HCl NaCl + H2O

Reaction:

2NaCl + 2H2O 2NaOH + Cl2 + H2

1.NaCl + CO2 + H2O + NH3

NaHCO3 + NHCl

2. 2NaHCO3 Na2CO3 + H2O

Uses :

NaCl : glazing the earthenware, regenerating water softeners and salting out of soap

KCl : fertilizer and others

(chlor-alkali process)

Solvay process to produce Na2CO3

Compounds of the elements

d) Hydrides- H atom – tendency to accept electron to form 1s2

- The electron affinity of H lower than Halide; small amount of energy released when hydride ion formed.

- Addition of electron causes electron-electron repulsion that increases the size of anion- By gaining an electron, H becomes anion, H- called hydride- Hydride forms only with least electronegative or highly electropositive metals.

Hydrides Properties Reaction Uses

-white crystalline solid

-reactivity increases down a group

Preparation:

M + H2 2MX (300-700 0C)

LiH

NaH, KH

Most stable, melts at 700 0C, decomposes at 1000 0C

-unreactive O2 and Cl2Decompose at 400 0C

8LiH + Al2H6 2LiAlH4 + 6LiCl

2NaH 2Na + H2

LiAlH4 : versatile reducing agent

Hydrides Properties Reaction Uses

-base Reaction:

NaH + H2O H2 + NaOH

4NaH + (CH3)3BO3 NaBH4 + 3CH3ONa

2NaH + B2H6 2NaBH4

NaH – good reducing agent; descaling iron and making NaBH4

Compounds of the elements

e) Carbonates

Carbonate Properties Reaction Uses

-Nature : Na2C03 , K2CO3

-Thermally stable; except Li2CO3

-Soluble in water; except Li2CO3 slightly soluble

Li2CO3 Li2O + CO2

Dissolve in carbonic acid form hydrogen carbonate solution

Li2CO3 – porcelain enamels Li2CO3 and glass

K2CO3 – to produce KCN and K2CrO4

Na2CO3 – from solvay process

Hydrate Na2CO3

Reactions Summary

1. 4M + O2 2M2O limited O2

2. 4Li + O2 2Li2O Excess O2 (Litihium oxide)

3. 2Na + O2 Na2O2 sodium peroxide

4. M + O2 MO2 M = K, Rb, Cs ; excess O2 (superoxide)

5. 2M + H2 2MH Molten metals

6. 2M + X2 2MX X = halogen

7. 2M + H2O 2MOH + H2 K, Rb, Cs – react explosively

Manufacturing of Sodium by electrolysis and its application

- Sodium : commercially produced by electrolysis of molten NaCl in the Downs Cell

- Mixture of NaCl and NaCl2 is electrolysed instead of pure NaCl (melts at 801 0C)

- The presence of CaCl2 reduces the melting point of the mixture to 580 0C, the eutectic mixture

- Graphite electrode : anode- Cylindrical steel : cathode

- Two electrode separated by an iron screen : to prevent molten Na contact with Cl2 form in the electrolysis Process : molten Na produced at cathode and floats to the surface of the liquid mixture because pure Na has lower density than liquid salt mixture, NaCl-CaCl2

- Liquid Na drawn off the electrolytic chamber into container which cools the liquid and finally freezes as solid sodium

- Cl2 gas liberated at graphite anode and flow to the top of reaction chamber into tank.

  Fused NaCl contains sodium and chloride ions.

2NaCl 2Na+ + 2Cl-

ELECTROCHEMICAL CHANGES 

At cathode Na+ ions migrate to cathode where they are reduced to Na.

2Na+ + 2e- 2Na (Reduction) At anode Cl- ions migrate to anode and oxidised to form chlorine gas.

2Cl- Cl2 + 2e- (Oxidation)

Overall Reaction

2Na+ + 2e- 2Na

2Cl- Cl2 + 2e-

2Na+ + 2Cl- 2Na + Cl2

- Application of sodium :

- chemical industries eg : glass, rubber, pharmaceutical

- as reducing agent in metallurgy such as titanium

- to manufacture drugs and dye

- sodium arcs(luminous discharege of electric current crossing a gap between two electrodes) – highway lighting