Friday, October 12, 2012

COVALENT BOND : ( chemical bonds )



               A bond between the two atoms are formed by the sharing of electrons. Which generally form between two non- metals. Example Nitrogen dioxide.

                Covalent compounds cannot dissociate into the water. So poor conductor of electricity in aqueous solution.

PROPERTIES OF COVALENT COMPOUNDS :

MOLECULAR FORM :
                   Covalent compound exist as a separate molecules. Because they are formed by neutral atoms and the force of attraction between these molecules is small.

STATE :
                   Due to weak inter molecular forces generally covalent compounds are liquid and gases. Some covalent substances are solid like iodine.

VOLATILITY :
                   They are volatile.

MELTING POINT AND BOILING POINT :
                   Generally they have low melting point and boiling point.

SOLUBILITY IN WATER :
                    Covalent compounds are generally in soluble in water.

SOLUBILITY IN THE ORGANIC COMPOUND :
                    Covalent compounds are non - electrolyte because they do not conduct electricity.

ELECTRICAL CONDUCTIVITY :
  •  Non polar covalent compounds do not conduct electricity.
  • Polar covalent compounds conduct small amount of electricity. 

IONIC BOND :




                          A bond between the two ions are formed from the transfer of one electron to another. Which is generally form between a metal and non-metal. For example NaCl. ( Sodium chloride ). This is often described as one atom giving electron to the other. In the case of NaCl , Sodium would give electron to chlorine.

                           Ionic compounds dissociate into their ions when they dissolve in water. It will react a good conductors of electricity in aqueous solution.

PROPERTIES OF IONIC COMPOUND:

STATE :
          Due to strong force of attraction, all ionic compounds are exist in solid state. At room temperature forming a crystal lattice structure.

THERMAL STABILITY :
            Ionic compounds have high melting point ( m.p) and boiling point (b.p )

CONDUCTANCE :
             They are strong electrolytes. In solid state they do not conduct electricity. In molten state and in aqueous solution they conduct electricity.

SOLUBILITY :
             Generally ionic compounds are soluble in water and  insoluble in organic compounds.

HARDNESS :
              They are very hard.

REACTIVITY :         
               Ionic compounds are very reactive .

THERMAL CONDUCTIVITY :
               Ionic compounds are low thermal conductivity.
  • Most of the ionic compounds are brittle and break under stress. Because ions produced by electron transfer attract each other by electrostatic attraction and this creates an ionic bond.

SINGLE BOND :


                A covalent bond formed by the mutual sharing of one electron pair between two atoms is called single bond. It is denoted by the single short line (-) In single bond formation each atom provide one electron. Usually single bond is sigma bond. But in diboron is pi bond .

Example :
      Single bond between the oxygen and each hydrogen in water molecule ( H2O ). Each of the covalent bond contains two electrons. One from hydrogen atom and one from oxygen atom. Both atoms share the electrons.

DELTA BOND :


              In chemistry delta bonds are the covalent chemical bond formed between the overlap of 4 d orbitals between two atoms. The Greek letter delta ( ) in their name refers to d orbitals. Some ruthenium and molybdenum compounds contain a quadruple bond, consisting of one sigma bond , two pi bond  and one delta bond.

Pi BOND :


    In chemistry pi bonds are the covalent chemical bonds formed between the two neighboring atoms unbounded P orbitals.
    An unbounded P orbitals electron in one atom forms an electron pair with the neighboring atoms unbound parallel P orbital electron. This electron pairs forms the pi bond. Double bond and triple bonds are usually made up of  single sigma bond and one or two Pi bonds. Pi bonds are generally denoted by the Greek letter ( ) . Pi bonds are usually weaker than the sigma bonds.    

SIGMA BOND :


                In chemistry sigma bonds are strongest type of covalent chemical bond. They are formed by direct overlapping between two adjacent atoms in the outer most orbitals. i.e Sigma bonds are the strongest type of covalent bonds due to direct overlap of orbitals and the electrons. In these bonds are sometimes reffered to as sigma electrons.Sigma bonds are most clearly defined for diatomic molecules using the language and tools of symmetry groups. Common forms of sigma bonds are S+S, Pz+Pz, S+Pz, and dz2+dz2.

                     Z ==> Defined as the axis of  bond.
sigma symbol is denoted by the Greek letter . 

Friday, October 5, 2012

Metallic Bond

                                 The reaction between molecules within metals are called alkali reactive force. It involve the sharing of free electrons among a lattice of metal atom.

PHYSICAL CHARACTERISTIC OF METALS :

  • Metals are strength, malleability, ductility, luster ( shiny appearance ) conduction of heat and electricity.
  • An alloy is a solution of metal , often used to make a metal rope, metal plates etc.
  • The electrons and the positive ions in the metal have a strong attractive force between them. So the metals have the high melting point Or boiling point.The principle is similar to that of ionic bonds.  
BONDING CHARACTERISTICS :
           The strength of metallic bond depends on three things.
  1. The number of electrons that becomes delocalized from the metal.
  2. The charge of the cation.
  3. The size of the cation.
  • Metals that are malleable can be beaten into thin sheets. For example aluminium foil.
  • Metals that are ductile can be drawn into wires. For example copper wire.

Intramolecular ( Strong )

Chemical Bonds:
  1. Ionic Bond
  2. Covalent Bond
  3. Metalic Bond 
Types of covalent bonds :
  • Sigma bond.
  •  Pi bond.
  •  Delta bond
  • Gamma bond
  • Single bond 
  • Double bond 
  • Triple bond
  • Quadruple bond 
  • Quintuple bond
  • Sextuple bond
  •  3c-4e  .   4c - 2e
  • Agostic bond 
  • Bent bond
  • Dipolar bond
  • Pi back bond
  • Hapticity
  • Antibonding
RESONANT BONDS :
  • Conjugation 
  • Hyper conjugation
  • Aromaticity
METALLIC BONDS :
  • Metal aromaticity.
INTRA MOLECULAR  - ( STRONG )
      
                            The force of attraction that exist between bonds within a molecule. They contain all types of chemical bond. They are stronger than inter-molecular forces.

TYPES OF INTRA MOLECULAR FORCES :                       

                            There are three main types of intramolecular forces distinguished by the types of atom and the behaviour of electrons.
  • Ionic bond
  • covalent bond
  • Metalic bond