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Saturday, April 17, 2021

Crystal lattice Structure of Oxides:


Related Questions:




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


Related Questions:

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, NiFetc 

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


Related Questions:

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

Related Questions:

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?

Question(12): NCl3 and PCl3 on hydrolysis give different kinds of products. These is because of