Effective atomic number

 

Effective atomic number

it was proposed by Sidwick, also known as Noble gas rule.

is defined as the resultant number of electrons with the metal atom or Ion after gaining electrons from donor atoms of ligands.

EAN = atomic number of the metal - number of electrons lost in ion formation + number of electrons gained from the donor atoms of the ligand.

Example-

1)   EAN for  [Co(NH₃)₆]³⁺

Solution:- Atomic no of Co =27

no. of electron lost by cobalt = 3

no of electrons gained from ligand =12 

 (since one NH₃ donates two electrons so, 6  NH₃ donates 12electrons) 

EAN = atomic number of the metal - number of electrons lost in ion formation + number of electrons gained from the donor atoms of the ligand.

therefore, EAN = 27-3+12 =36

2). EAN for [Ni(CO)₄]⁰      

Solution:- Atomic no of Ni =28

no. of electron lost by Ni = 0

no of electrons gained from ligand = 8   

(since one CO   donates two electrons so, 6 CO  donates 8electrons) 

EAN = atomic number of the metal - number of electrons lost in ion formation + number of electrons gained from the donor atoms of the ligand.

therefore, EAN = 28-0+8=36 

Limitations of valence bond theory

 Limitations of valence bond theory  

The valence bond theory was sadly successful in explaining qualitative only the geometry and magnetic properties of complexes however it has a number of limitations.  

these are as follow- 

• i) It involves a no. of assumptions such as electronic configuration, hybridization, overlapping etc. 

• ii) it does not give quality quantitative interpretation of magnetic data it does not explain the colour exhibited by coordination compound in does not give a quantitatively interpretation of the thermodynamic of kinetic stability is of coordination compound in does not make exact prediction regarding the tetrahedral and Square planar structure SOF 

• iii) it does not explain the colour exhibited by coordination compound  

• iv) it does not give a quantitatively interpretation of the thermodynamic of kinetic stability is of coordination compounds 

• V) it does not make exact prediction regarding the tetrahedral and Square planar structures of 4-coordinate complexes  

• Vi). It does not distinguish between weak and strong ligands. 

 Differences between inner orbital octahedral complexes and Outer orbital octahedral complexes 

Inner orbital octahedral complexes  or low spin complexes	Outer orbital octahedral complexes or high spin complexes
a. formed by hybridization of d2sp3 hybridisation. These are formed in the presence of strong ligands.   b. These complexes generally possess a smaller number of unpaired electrons i.e., they show either low or no magnetic moment.   c. These are less reactive i.e., more stable. Substitution reactions are difficult to occur.	a. formed by hybridisation of sp3d2 hybridisation. These are formed in presence of weak ligands.   b. These complexes generally possess greater number of unpaired electrons i.e., they show high magnetic moment.    c. These are reactive i.e., less stable. Substitution reactions are easy to occur.

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Limitations of Werner theory, Valance bond Theory

 

Limitations of Werner theory

 

 Werner was the first to describe the bonding feature in coordination compound but his theory could not explain followings aspects-

·    Certain elements possess the remarkable property of forming coordination compounds

·    The bonds in coordination compound have directional properties.

·    Coordination compounds have characteristic magnetic and optical properties

·    Could not explain the colour and electronic spectra of complex compound

·    Could not explain the pairing of electrons in the presence in the presence of some ligands

·    Could not explain the electrons distribution in the complexes

       many approaches have been forth to explain the nature of bonding in coordination compound. These are as

1). Valence bond theory (VBT)

2). crystal field theory (CFT)

3). ligand field theory (LFT)

4). Molecular orbital theory (MOT)

we will discuss about valence bond theory and Crystal field theory (as per CBSE syllabus)

Valance bond Theory

 Actually it is proposed by L.Pauling and J. L. Slater in 1935.it deals with the electronic structure of central metal ion in its ground state, kind of bonding, geometry and magnetic properties of complexes

This is based on the following assumptions –

·    Metal cation or atom should have empty (n-1) d ns np or ns np nd orbitals for the accommodation of electrons donated by the ligands

·       The Ligands have at least one sigma orbital containing a lone pair of electrons 

·    Empty orbitals of the metal cation or atom are hybridized and the empty hybrid orbitals overlap with the orbital of the ligand and as a result, coordinate or covalent bond is formed.it is represented by M←L.

_·    There are two types of ligand

(a) strong ligand - strong σ-donor example CO, CN^-, NO and

(b) weak ligand- weak σ-donor examples R^- Cl^- Br^- I^- H₂O

Note- generally NH₃ behaves as a weak ligand but in case of Cobalt ion it behaves as strong ligand.

·    Strong ligands have the tendency to pair up the electron in metal orbitals where as weak ligand have no such tendency. As a result of this there are two types of octahedral complex (d²sp³ or sp³d²) are formed

I)     Inner orbital complex- those complexes which is formed by using inner d-orbitals in

hybridization are called inner orbital complexes or low spin complexes.

II)   Outer orbital complex- those complexes which is formed by using outer d-orbitals

are called outer orbital complexes or high spin complexes or spin free complexes.

·   Tetrahedral complexes formed when sp³ hybridisation occurs.

·   Square planner complex also formed when dsp² hybridisation takes place.

·   Complexes having one or more unpaired electrons are called paramagnetic and the

complexes having no unpaired electrons are called diamagnetic

 Magnetic momentum (µ) = √n(n+2)  B.M. (Bohr Magnetons)

here n is no of unpaired electron

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Structural Isomerism in coordination compounds

 

Structural Isomerism-

·      structural isomers having same chemical formula but different structure.

·      This isomerism arises due to difference in structures of coordination compounds.

a). Linkage isomerism:

·      This type of isomerism occurs in complex compounds which contain ambidentate ligands like NO₂^-, SCN^-, CN^-

·      These ligands have two donor atoms but at a time only one atom is directly linked to the central metal atom of the complex.

Example

[Co (NH₃)₅N0₂] Cl₂                     <----->        [Co(NH₃)₅ONO]Cl₂

           Pentaamminenitrito-N-cobalt(III)          Pentaamminenitrito-O-cobalt(III)

                           chloride (yellow)                                  chloride (red)

b). Coordination position isomerism:

·      This type of isomerism is exhibited by polynuclear complexes by changing the position of ligands with respect to different metal atoms present in the complex

Example-

 [Co(NH₃)₆][Cr(CN)₆]  <------->  [Cr(NH₃)₆][Co(CN)₆]      

c). Ionisation isomerism :

·      this form of isomerism arises when the counter ion in a complex salt is itself a potential ligand and can displace a ligand which can become the counter ion.

Example-

[Co (NH₃)₅Br]SO₄       ------>  [Co (NH₃)₅SO₄]Br

 

d) solvate isomerism

·   This form of isomerism is known as hydrate isomerism when water is involved as a solvent.

·   This is similar to ionisation isomerism solvate isomer differ by whether or not a solvent molecule is directly bonded to the metal ion or merely present as free solvent molecules in the crystal lattice.

·    when different number of water molecules are present inside and outside the coordination sphere.

Example-

[Cr(H2O)₆] Cl₃          --------->[Cr(H₂O)₅Cl]C1₂·H₂O

दीपावली गोवर्धन पूजा एवं भाई दूज

"May the divine light of Diwali is spread into your life is prosperity happiness and good health"

"रोशन हो दीपक और सारा जग जगमगाए ले के साथ सीता मैया को राम जी हैं आए हर शहर लगे मनो अयोध्या हो आओ हरिद्वार हर गली हर मोड़ पर हम  दीप जलाएं "

                            

     

दिवाली देश का सबसे बड़ा त्योहार है इसे हम दीपावली के नाम से भी जानी जानते हैं इस दिन हर तरफ खुशी का माहौल होता है लोग रंग बिरंगी लाइटों से अपने अपने घरों को सजाते हैं और बच्चे युवा लोग मिलकर घरों के बाहर पटाखे छोड़ते हैं 

              लेकिन इस बार हमारे देश की विभिन्न राज्य  सरकारों ने पर्यावरण प्रदूषण को कम करने के क्रम में पटाखों पर रोक लगा दी है क्योंकि पटाखों से वायु प्रदूषण होता है इसलिए यह त्योहार इस बाहर  काफी महत्व  का हो गया है यह कदम  सरकारों का  काफी सराहनीय है  इसमें हमें सरकार को सहयोग देना चाहिए।

             वैसे यह त्योहार 5 दिन तक मनाया जाता है पहले दिन धनतेरस के रूप में जाना जाता है जिसे लक्ष्मी की पूजा करके मनाया जाता है लोग देवी को खुश करने के लिए आरती भक्ति गीत गाया जाता है आते हैं दूसरे दिन नरका चतुर्दशी यहां छोटी दीवाली के रूप में जाना जाता है जिसे भगवान कृष्ण की पूजा करके मनाया जाता है क्योंकि उन्होंने राक्षस राजा नरक सुर को मार डाला था तीसरे दिन मुख्य दिवाली दिवस के रूप में माना जाता है जिसे शाम को रिश्तेदारों दोस्तों पड़ोसियों और जल्दी फायरक्रैकर्स के बीच मिठाई और वह वितरित करते हुए देवी लक्ष्मी की पूजा करके मनाया जाता है चौथे दिन भगवान कृष्ण की पूजा करके गोवर्धन पूजा के रूप में जाना जाता है लोग अपने दरवाजे पर पूजा करके गोबर के गोवर्धन बनाते हैं  पांचवां दिन यम द्वितीया या भाई दोस्त रूप में जाना जाता है जिसे भाइयों और बहनों द्वारा मनाया जाता है बहनों ने अपने भाइयों को भाई दूज बनाने के लिए आमंत्रित करती है और यह त्यौहार सद्भावना का   त्योहार  है

  " आओ हम सब मिलकर  हमारे देश को समृद्ध एवं  विकसित बनाएं "

                        

                          

                                    

                                                  "जय हिंद ,जय भारत"