Chemqueries: June 2020

Monday, 22 June 2020

What are the 7 types of Crystals


7-types of crystals:

On the basis of axial length in x,y, z-direction, and interfacial angles between them,unit cell can be classified into seven types which are called Seven Crystal System.
7- Crystal Habits
Axial Length
Interfacial Angles
Cubic
a = b = c        
α = β = γ = 90˚
Tetragonal
a = b c        
α = β = γ =90˚
Orthorhombic(Rhombic)
a ≠ b ≠ c        
α = β = γ =90˚
Monoclinic
a ≠ b ≠ c        
α = γ =90˚ ,  β 90˚
Triclinic
a ≠ b ≠ c        
α β γ 90˚
Hexagonal
a = b ≠ c        
α = β = 90 ˚ , γ =120˚
Rhombohedral
a = b = c        
α = β = γ 90˚
Where a,b,c is the length of x,y and z-axis respectively.
α,β,γ  is the interfacial angle between x-axis and y-axis, y-axis and z-axis, z-axis and x-axis respectively.

Note:

Most symmetric crystal -Cubic Crystal
Most unsymmetric crystal -Triclinic Crystal
To remember this crystal system we have derived a formula and i.e. 
            CUTE OUR MOTHER
CU-Cubic
TE-tetragonal
OUR-Orthorhombic
MO-Monoclinic
T-Triclinic
HE-Hexagonal
R-Rhombohedral

Saturday, 20 June 2020

Chemqueries: UNIT CELL

Chemqueries: UNIT CELL: What is unit cell? The smallest part of the complete space lattice which on repetition again and again in all the possible direction resu...

UNIT CELL

What is unit cell?

The smallest part of the complete space lattice which on repetition again and again in all the possible direction results in the formation of crystal lattice/space lattice is called a unit cell.

Contribution of a lattice point at a particular position:

location             Contribution
Body center       1
Face center        1/2
Edge center       1/4
Corner               1/8

Classification of the unit cell?

On the basis of the location of the lattice point within the unit cell, there may be two types of unit cells.

1st classification of unit cell

1.Primitive unit cell

In this type of unit cell lattice points are present only at corners.
For example SCC(Simple Cubic Unit Cell)
Lattice points at the corner
Coordination number(Z)=8*1/8=1

2.Non-Primitive unit cell

In this type of unit cell lattice points are present not only at corners but also at some other specific position. For example,
(a)BCC(Body center cubic unit cell)
Coordination number(Z)=Lattice point at corner+Lattice point at the body
                                        =(8*1/8)+1=2
(b)FCC(Face center cubic unit cell)
Coordination number(Z)=Lattice point at all corner+lattice point at each face
                                        =(8*1/8)+(6*1/2)
                                        =1+3=4
Where the coordination number(Z)is the total number of particles or atoms or lattice points per unit cell.

2nd classification of unit cell:

On the basis of axial length in x,y, z-direction, and interfacial angles unit cell can be classified into 7 types which are called seven crystal system or seven crystal habits and these are Cubic, Tetragonal, Orthorhombic(Rhombic), Monoclinic, Triclinic, Hexagonal, Rhombohedral.
For brief understanding about the above seven crystals, follow the link below:

Tuesday, 9 June 2020

Chemqueries: METAL CARBONYLS

Chemqueries: METAL CARBONYLS: What is metal carbonyls? Carbon monoxide is undoubtedly one of the most important and most widely studied ligand in organometallic chemist...

METAL CARBONYLS

What is metal carbonyls?
Carbon monoxide is undoubtedly one of the most important and most widely studied ligand in organometallic chemistry. Almost all of the transition metals from metal carbonyls (the complex containing only CO as ligands)and these homoleptic carbonyls are useful precursors for other organometallic compounds.
Though carbon monoxide is not considered as a very strong lewis base, yet it forms a strong bond to the metals in their complexes.
In most of the metal carbonyls, the metals are always in low oxidation state, most often in the oxidation state of zero but sometimes -1 or +1, and these carbonyls are often quite stable with respect to dissociation, substitution or oxidation.CO may bond to a single metal or it may act as a bridge between two or more metals. The number of CO ligands considered to the metal is generally in accordance with the 18-electron rule and this rule is followed by 99% of the metal carbonyls.
Classification of Metal Carbonyls:

1.Classification on the basis of ligands:

Metal carbonyls can be classified into two categories:

(i)Homoleptic carbonyl complexes: The complex in which the metal is bound to only CO as ligands are known as homoleptic carbonyl complexes.for example, Ni(CO)4, Cr(CO)6,Fe(CO)5,Co2(CO)8,Mn2(CO)10,Fe3(CO)12,Ir4(CO)12 etc.

(ii)Heteroleptic carbonyl complexes: The complexes in which a metal is bound to CO as well as other ligands such as PR3,PPh3,PF3,NO.RNC etc.For example, Ni(CO)3PPh3,Mo(CO)3(PF3)3,Cr(CO)3(NO)2 etc.

2.Classification on the basis of a number of metal atoms and the structures of Metal Carbonyls:

(i)Mononuclear Metal Carbonyls: These carbonyls contain only one metallic atom and these carbonyls do not contain any bridging CO ligand.For example Ni(CO)4,Cr(CO)6,Fe(CO)5 etc.

(ii)Polynuclear Metal Carbonyls: Polynuclear carbonyls contain only one or two metal atoms and these are classified as 

(a)Homonuclear Metal Carbonyls: These contain metal atoms of only one element.For example Fe2(CO)9,Mn2(CO)10,Co2(CO)8,Fe3(CO)12,Co4(CO)12,Rh4(CO)12,Ir4(CO)12 etc.
(b)Heteronuclear Metal Carbonyls: These carbonyls contain metals of different elements.For example,MnCo(CO)4
The polynuclear metal carbonyls are also classified as:
(a)Non-bridged Metal Carbonyls: These carbonyls contain terminal CO ligand and M-M bonds.For example,Co2(CO)8 (In solution),Mn2(CO)10,Ir4(CO)12 etc.
(b)Bridged Metal Carbonyls: These carbonyls contain bridged as well as terminal CO ligands and M-M bonds.For example,Fe2(CO)9,Co2(CO)8 (in solid state),Fe3(CO)12 etc.

Thursday, 4 June 2020