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Saturday, April 17, 2021
Corundum (Al2O3) type Structure:
This type structure is exhibited by oxides of trivalent metals for examples Fe2O3, Al2O3, Cr2O3, Mn2O3 etc.
General formula is M2O3:
In Corundum Structure:
O-2 = ions forms HCP unit
cell:
M+3 = Occupied 2/3 (66.66%) of octahedral voids (OV): and
33.33% OV are empty and TVs are 100% empty.
In Hexagonal close packing
(HCP): Formula determination:
O-2
= HCP = O6
M+3=2/3 x 6 = M4
=M4O6 or M2O3
What are the normal spinel structures?
Rutile (TiO2) type Structure:
This type of structure is represented by TiO2 and other example are includes MnO2 , SnO2 , MgF2, NiF2 etc
In Rutile structure:
O-2 = ions forms hexagonal cubic
packing (HCP).
M+4 =Tetravalent cations are occupied 50 % (1/2) of octahedral voids (OV) while all the tetrahedral voids (TO) are empty.
HCP= Lattice points (LP) = O-2=
6
M+4 ions
= OV (50%) =6 x 1/2 = 3
M3O6
= MO2
It means
each HCP unit cell certain three (M+4 ) and six (O-2 )ions
What are the normal spinel structures?
Pervoskite (ABO3) type structure:
ABQ3 is a proto type solid where A is
a divalent
cation and B is a tetravalent cation.
A+2 = Divalent cations
B+4 =Tetravalent cations
In Pervoskite structure:
A+2 = placed at corner of cubic unit cell
O-2 = placed at all the face centre
That
means A+2 and O-2 ions combinelly form CCP/FCC
like structure and
B+4 = Tetravalent cations occupy the central octahedral voids (25% of
total OV) i.e centre of the centre of the unit cell so general formula is ABO3
Other
examples are BaTiO3, SrTiO3
What are the normal spinel structures?
Tuesday, February 16, 2021
Both CO2 and N2O are linear but dipole moment of CO2 is zero but for N2O it is non-zero, why?
The answer lies in the structure of these molecules, CO2 is symmetrical molecule while N2O is unsymmetrical, thus for N2O, dipoles do not cancel each other, leaving the molecule with a resultant dipole, while the bond moment of CO2 cancel each other, so CO2 has no net dipole moment.
Related
Questions:
Question(1): Why aqueous solution of AlCl3 is acidic in nature ?
Question(2): What happen when aq AlCl3 react with Acid or Base?
Question(3): Although anhydrous aluminium chloride is
covalent but its aqueous solution is ionic in nature. Why?
Question(4): Arrange in increasing order of extent of hydrolysis [ CCI4, MgCI2,
AICI3, PCl5, SiCI4].
Question(5): Although Sulphur contain vacant d-orbital but SF6 does not undergo
hydrolysis. Why ?
Question(6): CCl4 can not be hydrolysed but SiCl4 can be. Why?
Question(7): What
are the hydrolysis products of urea ?
Question(8): Why
SF6 is inert where as SF4 is highly reactive towards H20
?.
Question(9): Why
SF6 behave inert towards hydrolysis?
Question(10): Why PCl3 hydrolysed while NCl3 can not be hydrolysed?
Question(11): Why hydrolysis
of NCl3 gives NH4OH and HOCl, while PCl3 on hydrolysis gives H3PO3 and HCl?