What is EAN(effective atomic number) and how to calculate EAN ~ NEET chemistry

EAN ( Effective atomic number) represents the total number of electrons surrounding the nucleus of a metal atom in a metal complex.

It is the composition of the metal atom's and the bonding electrons from the surrounding electron donating atoms and molecules.

By the calculation of EAN we will find the stability of the complex .

Every complex trying to get inert gas configuration because inert gas configuration is a stable configuration.

3d metals complex trying to rich 36 electrons in its surrounding.

4d metals gets 54 electrons and 5d metals gets 86 electrons in its surrounding.

Quest. :--How to calculate. EAN?

Ans. :-- We caculate EAN by two methods :--

(1) By the help of NAM(neutral atom method.

(2) By the help of 18 electron rule.

Quest:--- what is formula of calculating EAN ?

(1) Formula for NAM method.

= total number of electron of central atom + total number of electron given by all the ligands ± charge

(2) Formula for 18 electron rule

= Total number of valence electron of central atom +total electron given by all the ligands ± charge

Note :--- Here charge is add when negative charge is present on complex where as charge is subtract when charge is positive on complex.
Atomic Number of element is equal to the total number of electron of central atom.
Atomic no. is equal to no of protons and no of electrons.

Some important points related to EAN calculation.

Each neutral donar site contribute 2 electron for the calculation of EAN.
2. Each ionic ligand contribute. electron according to thier. charge.

Some examples of ligands and their electron contribution in EAN calculation.

(i) 1 electron donar ligands:--- all halogens, OH-, CH-, oac-,H- , NC-, NCO-, OCN-, NH2^- , SH-, NO2^- , ONO-, ( sigma-C5H5) ,Alkyl, CN-

(ii) two electron donar ligands:-- H2O, NH3, CO, R-NH2, CS, Py, PR3, PF3, PCl3, CO3^2- , SO4^2- , S2-, O^2-, SO3^2- , O2^2- , NH2-, ox2-, carbine(:CH2) ,

(iii) three electron donar ligand:-- N^3- , PO4^3-, glycinato, acac-,

(iv) four electron donar ligand :-- en, bipy, DMG-

Example to see how to calculate EAN in coordination compound.

[Fe2(CO)9]

To calculating oxidation state of central metal ion. Oxidation state shows the charge of complex in its outer sphere. Sometimes this charge is cancelled by positive or negative ion.

If complex contain negative charge in its outer sphere than positive ion neutral this charge whereas positive charge neutral by negative ion.

In above example there is no charge in its outer sphere.

In above example Fe is a central atom. Atomic no of Fe is 26 so the total no of electron of central atom is 26.

Here CO( carbonyl group） is a neutral donar ligand. So, it's donate only two electron to central metal ion.

Applying neutral atom method formula of calculating EAN

= 26+ (2*5)±0 = 26+10. = 36

It follows EAN rule.

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