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Friday, March 27, 2020

Ligands-definition-examples-types in co-ordination chemistry .

Ligand definition in co-ordination chemistry

In co-ordination chemistry, the cation to which one or more neutral molecules or ions are co-ordinated is called centralmetal cation, while the molecules or ions so attached are called Ligand.

For examples , CN^–, Cl^–, CO , H₂O NH₂–NH₂ etc.

Ligand examples in co-ordination chemistry

There are three types of ligands depending on the nature of charge are known . Such as cationic ligand, anionic ligand and neutral ligand.

Ligand types in co-ordination chemistry

There are different types of ligands are known depending on their function in co-ordination with the central metal ion in co-ordinationchemistry .

Such as ambident ligands , flexidentate ligands , classical ligands, non-classical ligands, chelating ligand, π-acid ligand etc.

Ambident ligands.

There are few ligands which contain more than one donor atom, but they can use only one donor atom at once in the formation of complex compound, these type of ligands are called Ambident ligands.

There are two types of ambident ligand, namely, mono dentate ambident ligand and bidentate ambident ligand.

When a mono dentate ambident ligand ( such as nitrite ion ) ,is attached with different central metal ion , it uses either ‘N’ atom or ‘ O ‘ atom as a donor atom .

Similarly, when a bidentate ambident ligand ( such as dithio oxalate ion ), is attached with different central metal ion, it uses either both the ‘O’ atom or both the ‘S ‘ atom together as a donor atom.

Flexidentate ligands

There are few ligands in co-ordination chemistry which have two or more donor atoms.

But ,they do not use their entire donor atom at once in the formation of co-ordination compound that is in co-ordination with central metal ion .

They use their different donor atom with different metal ion to form co-ordinate bond . Such types of ligands are called flexi dentate ligands.

For example, Cysteine, a tri-dentate ligand with three different donor atoms ( S, N, O ) act as a di dentate ligand in three different way [ when it uses S,N , N,O and S,O atom separately ]

So, Cysteine is a flexi dentate ligand.

Similarly, there are many other poly dentate ligands those are behaved as a flexi dentate ligand.

Such as, EDTA , a poly dentate ligand , but in some cases it uses as a penta dentate or tetra dentate ligand. So, EDTA is also a flexi dentate ligand.

There are another two types of ligands are known which are, classical ligands and non-classical ligands .

( I ) Classical ligands : Classical ligands are those ligands which can co-ordinate with the central metal ion by using their lone pair of electrons .

For examples CO , CN^– , F ^–, Cl ^– , OH ^–, H₂O , NH₃ etc .

(II ) Non-classical ligands : There are few ligands which uses their electron-pair of pi bond in the formation of co-ordinate bond with the central metal ion , these type of ligands are called Non-classical ligands.

For examples C₂H₄ , C₆H₆ , C₅H₅ – [ cyclo penta dienyl anion ] etc.

Summary :

Ligand definition in co-ordination chemistry
Ligand examples in co-ordination chemistry
Ligand types in co-ordination chemistry
What is ambidentate ligands ?
What is flexidentate ligands ?
What is classical ligands ?
What is non-classical ligands ?

Complex compound definition in chemistry .

Complex compounds-definition-examples-perfect-imperfect complex definition.

BY P GHOSH Complex compounds-definition-examples-perfect-imperfect complex definition. , HOME

Complex compounds or co-ordination compounds definition in chemistry

There are a large number of molecular compounds which maintain their identities even when dissolved in water or any other solvents and their physical and chemical properties are completely different from those of the constituents, are called complex compounds or co-ordination compounds.

For example, potassium ferro-cyanide, K₄[ Fe ( CN ) ₆ ] . Potassium ferro-cyanide is obtained by the reaction of Fe(CN )₂ and KCN.

Besides this, there are many other examples of complex compounds. Such as, [Co ( NH3 )₆ ] Cl₃ , [ Ni ( NH₃ )₆ ]Cl₂ , [Pt ( NH₃ )₂ Cl₄ ] , K₂[ Pt Cl₄ ] , K₂[ Hg I₄ ] etc.

What is imperfect complex ion or complex compound?

Complex ions or co-ordination entity that can not maintain their independence existence in solution and they are dissociated into their constituents ions partially,

those complex ions are called imperfect complex ion or complex compound.

For example, potassium tetracyanido cadmate(II) with molecular formula, k₂[Cd ( CN )₄ ]. k₂[Cd ( CN )₄ ] is dissociated in solution into K ⁺and [ Cd ( CN ) ₄ ] ^2- ion.

Then, [ Cd ( CN ) ₄ ] ^2- ion is further dissociated and released free central metal ion , Cd ²⁺ and Ligand CN ^{– .}

What is imperfect complex ion or complex compound ?

We can proved it by passing H₂S gas through this solution . If we passed H₂S gas through this solution, a yellow color precipitation of CdS is appeared which proved the existence of free Cd ²⁺ ion in solution.

What is perfect complex ion or complex compound ?

Complex ions or co-ordination entity that exhibit very much less degree of dissociation in solution and hence maintain their independence existence in solution completely,

those complex ions are called perfect complex ions or complex compounds.

For example, K₃[Cu ( CN )₄ ] complex compound is dissociated in solution into K ⁺and [ Cu ( CN )4 ]^3– complex ion.

What is perfect complex ion or complex compound ?

But if we passed H₂S gas through this solution, no precipitation is found. This means that, [ Cu ( CN )4 ]^3– complex ion remain unchanged in solution .That is, it is stable in nature.

Summary

Complex compounds or co-ordination compounds definition in chemistry.
Complex compounds or co-ordination compounds examples.
What is perfect complex ion or complex compound ?
What is imperfect complex ion or complex compound?

Double salts definition co-ordination chemistry.

Co-ordinate covalent bond-definition-examples-formation conditions.

BY P GHOSH Co-ordinate covalent bond-definition-examples-formation conditions. , HOME

Co-ordinate covalent bond definition in chemistry

If one of the two participating atom in a chemical attachment, provide one pair of electrons and both they complete their octet by sharing this electron pair, then the

power of the two participating atom for the attachment to each other, is called co-ordinate covalency.

Co-ordinate covalent bond definition in chemistry

The chemical bond which is created due to co-ordinate covalency is called co-ordinate bond.The co-ordinate bond is also called dative bond.

Although co-ordinate bond is also one type of covalent bond. But this bond is polar in nature. Because, the donor atom gets positive charge and the acceptor atom gets negative charge.

Like covalent bond, co-ordinate bond is also produced by the overlapping of two atomic orbital .

Since the atomic orbital has a specific direction , hence co-ordinate bonds are also have a specific direction.

What is co-ordinate covalency?

If one of the two participating atom in a chemical attachment, provide one pair of electrons and both they complete their octet by sharing this electron pair, then the

power of the two participating atom for the attachment to each other, is called co-ordinate covalency.

Co-ordinate covalent bond examples .

There are many examples of co-ordinate covalent bond or co-ordinate covalency .

Such as , NH₃.BF₃ , LiAlH₄ , NaBH₄, NH₄Cl, Al₂Cl₆ etc compounds contain co-ordinate covalent bond .

Formation of co-ordinate covalent compound, like NH₃.BF₃ is shown below .

The nitrogen atom in ammonia have one lone pair of electrons . On the other hand, the boron atom in BF₃molecule have incomplete octet.So B-atom have a tendency to gain two electrons for completion of its octet.

Hence, in reaction between ammonia and boron tri-fluoride, ‘N’-atom of ammonia molecule acts as electron donor and ‘B’-atom in BF₃acts as electron acceptor.

But both they complete their octet by sharing of electron pair equally . In this way , NH₃ and BF₃ molecule form a co-ordinate covalent bond to each other, resulting in the formation an adduct compound.

Now, the molecules or ions which give up electron pair, they are called Lewis base and the molecules or ions which accept electron pair, are called Lewis acid. Hence, here NH₃ acts as a Lewis base and BF₃ acts as a Lewis acid.

Co-ordinate covalent bond formation conditions

( I ) Between the two participating atoms, the donor atom must have one lone pair of electron.

( II ) The acceptor atom must have a vacant orbital so that the atom can accept the lone pair of electrons.

( III ) The complete displacement of electrons from donor atom to acceptor atom does not occur. Both the atom ( donor and acceptor ) shall be use the electron pair equally.

Characteristics of co-ordinate covalent compounds .

Co-ordinate covalent bond is one type of covalent bond. So the characteristics of co-ordinate covalent compounds are similar to that of covalent bond .

( I ) Co-ordinate covalent compounds may be solid, liquid or gaseous in room temperature .

( II ) Co-ordinate covalent compounds are polar in nature. Actually Co-ordinate covalent bond is more polar than covalent bond and less polar than ionic bond.

Consequently, the melting and boiling point of Co-ordinate covalent compounds are higher than covalent compounds but less than ionic compounds.

(III ) Co-ordinate covalent compounds have a co-ordinate covalent bond . But all other bonds are covalent bond.

Hence Co-ordinate covalent compounds are soluble in non-polar solvent ( benzene , carbon disulfide, carbon tetrachloride etc )but the solubility in polar solvent is very much less .

( IV ) Compounds with co-ordinate covalent bond does not ionize in aqueous solution as well as in melting condition.So they can not conduct electricity.

( V) Co-ordinate covalent bond is rigid and they have specific direction . So co-ordinate covalent compounds show isomerism properties .

Why does AlCl₃ exist as a diner ?

The chlorine atom in AlCl₃molecule have three lone pair of electrons . On the other hand, ‘Al’-atom have incomplete octet .

So ‘Al’-atom have a tendency to gain two electrons for completion of its octet.

Hence, Cl-atom of one AlCl₃ molecule donate electron to the Al-atom of another AlCl₃ molecule and form a co-ordinate bond.

But both they complete their octet by sharing of electron pair equally . In this way , two AlCl₃molecule form a co-ordinate covalent bond to each other, resulting in the formation of a dimer molecule Al₂Cl₆ .

Now, the molecules or ions which give up electron pair , they are called Lewis base and the molecules or ions which accept electron pair , are called Lewis acid.

Hence, here chlorine atom acts as a Lewis base and ‘Al’-atom acts as a Lewis acid.

Why BCl₃ trigonal planar but AlCl₃ tetrahedral?

Boron atom in BCl3 molecule is sp2 hybridized. Three half filled hybridized orbital of ‘B’-atom is overlapping with the three half filled p-orbital of ‘Cl’-atom ,resulting in the formation of trigonal planar BCl₃ molecule .

Boron atom can not attach with four chlorine atom due to its small size .Hence, the geometry of BCl₃ molecule is trigonal planar.

On the other hand, chlorine atom in AlCl₃molecule have three lone pair of electrons and ‘Al’-atom have incomplete octet. So ‘Al’-atom have a tendency to gain two electrons for completion of its octet.

Why BCl3 trigonal planar but AlCl3 tetrahedral ?

Hence, ‘Cl’-atom of one AlCl₃ molecule donate electron to the ‘Al’-atom of another AlCl₃ molecule.

In this way, two AlCl₃molecule form a co-ordinate covalent bond to each other, resulting in the formation of a dimer molecule Al₂Cl₆. For this reason, the shape of AlCl₃ molecule is tetrahedral.

Summary

Co-ordinate covalent bond definition in chemistry
What is co-ordinate covalency ?
Co-ordinate covalent bond examples .
Co-ordinate covalent bond formation conditions .
Characteristics of co-ordinate covalent compounds .
Why does AlCl3 exist as a diner ?
Why BCl3 trigonal planar but AlCl3 tetrahedral ?

Ionic bond definition examples properties.

Ionic bond-definition-example-properties and formation condition .

BY P GHOSH HOME , INORGANIC

Ionic bond definition in chemistry

Ionic bond or electro-valent bond is one type of chemical bond which is formed by the force of electrostatic attraction between cation and anion .

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Friday, March 27, 2020

Ligands-definition-examples-types in co-ordination chemistry .

Ligand definition in co-ordination chemistry