Covalent Bonding and Lewis dot model or Electron dot model

Covalent Bonding 

Definition: A chemical bond formed by mutual sharing of electrons between two atoms is called covalent bond
Covalent bond formed between two atoms:
·      If the electronegativity value difference is less than 1.7
·      Each atom contributes electrons equally for sharing.
·      The sharing takes in pairs
·      The shared electron pair belongs to both the bonded atoms. The sharing can involve in
1.    One pair of electrons, Single bond (-) formed
2.    Two pairs of electrons, double bond (=)
3.    Three pairs of electrons, Triple bond (≡) 

Lewis dot model or Electron dot model :


·      Electrons present in the outer shell only are used for bonding
·      The sharing of outer electrons results the covalent bond
·      The bonded atoms get octet configuration to get stability
·      Each valence electron of bonded atom is regarded as a point charge indicated as ‘dot’

Example 1: Hydrogen molecule (H2)
·      Hydrogen atom has a single electron in 1st orbit
·      It requires one more electron to attains stability
·      Each atom contributes one electron
·      Electron pair is shared between two hydrogen atoms.
·      A single bond is formed between hydrogen atoms


Example 2 : Oxygen Molecule (O2)
·      Oxygen atom has 6 valence electrons
·      Out of 6 valence electrons, 2 are unpaired
·      It requires 2 electrons to attains stability.
·      Two oxygen atoms share their unpaired electrons to get stability.
·      A double bond is formed between two oxygen atoms. 


Example 3: Nitrogen molecules (N2)
·      Nitrogen atom has 5 valence electrons
·      3 electrons are unpaired
·      It requires 3 electrons to attain stability
·      Two nitrogen atoms share their unpaired electrons to get stability
·      A triple bond is formed between two nitrogen atoms


 Example 4: Hydrogen chloride (HCl)
·      Hydrogen atom contains only one electron
·      Chlorine has 7 valence electrons in which one unpaired electron
·      The unpaired electron of chlorine is shared with hydrogen’s electron.
·      Both the atoms get stable configuration
·      A single bond is formed




·      Non-polar covalent bond
A covalent bond formed between similar atoms
Ex: H2,O2,N2,Cl2 etc..
·      Polar covalent bond
A covalent bond formed between dissimilar (different type) atoms.
             Ex: HCl, H2O, NH3 etc….


Characteristics of covalent compounds 

·      The compounds are gases or volatile liquids
·      These Possess low melting and boiling points
·      Usually non-polar compounds.
·      These are Soluble in non-polar solvents, like Alcohol, Benzene, etc.
·      These are Insoluble in water
·      They do not conduct electricity because lack of ions in solution.
·      Exhibit isomerism
·      Chemical reactions are slow, and often very slow between them. 


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