Electron deficiency:

Electron deficiency If there are too few valence electrons in compound. For the connection between atom to be Described as Covalent bonds electron deficient bond are often better described as 3, canter 2,electron bond.
The boran is an example of compounds that are deficient in electrons.

Electron theory of chemical bonding :

          G.N Lewis and W kossel working independently used the knowledge of electronic configuration.
To explain why atoms joined to form molecules. They visualised that noble gas atoms had a stable electronic Configuration ns2 np6. Except He who is 1s2 while atoms of all other elements had electronic configuration of an unstable or incomplete shell of valence.

The electronic theory of chemical bonding was brought forward in 1916.
This states that atoms in the formation of chemical bonds interact by losing electrons gain or sharing. So as to Achieve a stable noble gas configuration. Thus molecules are formed by redistribution of electrons between
Two or more atoms .

We say atoms respond to the acquisition of two duplet electrons.Thus molecules are formed or eight electron octet structure H LI And Be atoms tend to acquire a duplet and all other atom  tend to attain the octet configuration.

Types Of Chemical Bonds:

1: Ionic bond
2: Covalent bond
3: Coordinate covalent bond
4: Metallic bond
5 : Vander walls and long range bond

 Ionic Bond:

      An ionic bond is the result of electrostatics attraction between positively charged cations and negatively Charged anions. Which can be formed by the transfer of one or more electrons from one atom or group of atoms to another.

One atom loses from one or more electrons to form a cation and the other gain one or more electron to become an anion. So as to attain the nearest noble gas electronic configuration. Ionic bonding occur mostly the
Element with low ionization electron negativity and high electron affinities. Find chlorine-based sodium reaction to form sodium chloride.

             Na  1/2 cl2    →      NaCl

In this reaction we can picture three major transformations sodium atom loses one electron to form sodium ions NA to attain the noble gas neon electronic configuration. The energy required for the formation of NA Ions from Na in the gas phase is 496 kg/mol. Which is simply the first ionization of Na.

             Na   →        Na and e

The chlorine atom gains an electron to form chlorine ions to attain the noble gas argon electronic configuration and releases energy 349kj/mole.


  It is often said that NaCl is a stable compound because both Na and Cl ion in NaCl have the stable electronic configuration of a noble gas.

However the energy data cited above show that the completion of noble gas shells cannot account for the stability of NaCl.

Electron deficiency:

  Electron deficiency occurs when compound has too few valence electrons to be identified as covalent bonds for the relation between atoms.Deficient electron bonds are often better described as 2-electron bond 3-center bonds.

Covalent Bond:

      A chemical bond formed by the mutual sharing of electron between two atoms is called covalent bond.

Each atom contributes one electron of its valence shell to be shared electron pair. The pairing of electron according to Lewis should lead to a noble gas configuration. The mutually shared pair of electrons is considered to be possessed by both the atom in common. Which would contribute to the electronic configuration of each atom in the the molecules.

The sharing of electrons by two atoms in a covalent bond is energetically favourable. If two isolated atoms form covalent bond, energy is released.

Because the electrons exchanged tend  to lie between the two nuclei bound. 

Both nuclei draw the mutual electrons. At the same time the nucleoli of two atoms also repel each other as do the two electrons. The repulsion of the nucleoli is off set by this attraction. It is the net attractive force between the shared electron together .

Covalent bond;

The attractive force between atoms create by sharing of an electron pair is called Covalent bond.

Lewis structure.

A share electron pair can be represent either by two dots or by a line between the two bonded atoms. Although lewis used only dots modern structure generally use line to represent share electron pairs.Such structure are called Lewis structure.

Atoms of the same electronegativities  or low having one valence electron. Each contributes an electron to the shared pair and both atoms acquires the stable electronic configuration. Resulting a stable H2 molecules.

            H+H → H+ H

In Cl2 molecules shared electron pair and both the chlorine atoms achieve a stable octet. Thus each cl acquire the stable electronic configuration of the noble gas organ.

        Cl+Cl → Cl -Cl.

Non bonding:

Note that each Cl atom has pairs of electrons that are not involve in bonding. These electron are called non bonding.

Certain atom may share more then one pair of electron to achieve an octet. Two atoms form a single covalent bond. When they share one pair of electron a double covalent bond when they share three electron pairs.

     O+O → O::O
     N+N → N:::N
     H+H → H:H

Lewis dot formula:

Lewis dot formula Can also be use to represent atoms covalently bond in a molecule or poly-atomic ion.

The covalent bonds are of two types:

  1. polar 
  2. non polar

Non polar:

A covalent bond between two like atoms. Such as H-H Cl-Cl in which the electron pair is shared equally between the two nucleoli is called a non polar.

Polar covalent bond:

A covalent bond between two unlike atoms. Such as H-Cl,H-BR. In which the electron pair is shared unequally and the bonded atom acquire a partial positive and negative charge is called a polar covalent bond.

BF3 has polar bond but the BF3  molecules is non polar whose geometry is trigonal planner.

The three bond moments are of equal magnitude. They point to corner of an equilateral triangle. The bond moment cancels due to the molecule’s symmetry.

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