Post on 18-Jan-2016
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