CHEMICAL BONDS IT'S TYPES

Force of attraction which hold two atoms together is called chemical bond.                                         
Example: H + H ------> H2 + heat                                                                                                     

why atoms form bond?                                                                                                                     
There are two main reasons due to which atom form bond.                                                       

Reason No 1: When two atoms combine to form a bond then heat is released, so the form substance become more stable at low energy.Thus atom form bond to acquire more stability at low energy.                                                                                                                                                             
Reason No 2: Atom form bonf=d to acquire the noble gas electrinic configuration in the valance shell.In noble gasses hilium has first valance shell and it has two noble gasses have eight electrons (octet) in valance shell.Generally noble gasses are stable and do not form bond like other elements.Thus ataom of other element form bond to acquire noble gas electronic configuration two electrons for the first valance shell and eight electrons for the other valance shells.                             

Types of Chemical Bond:

Different types of chemical bond are given below.
                                                                       
1)Ionic or Equivalent Bond
Bond form by transfer of one or more electron from the valance shell of one atom to the valance shell of other atom is called ionic bond.
or
Electrostatic force of attraction between cations and anions is called ionic bond.                               

Explanation:

Ionic bond is formed between metal andnon metal atoms if difference of electronagativity between them is more than 1.7.Metal atoms has low ionization potential and low electronagativity so they give electrons easily.Non metal atom has hugh electronagativity and high electro affinity so they gain electron easily.Thus in ionic bond metal give electron to acquire noble gas electronic configuration and change into cations and non metal  atom gain electron to acquire noble gas eletronic configuration and change into anions.Then the force of attraction take place between cation and anion that combine them together and is called ionic bond.

Example: Formation of Nacl sodium give one electron and chlorine gain one electron and both acquire noble gasses electronic configuration.                                                                         

Reaction: Na + Cl -----> NaCl   DH = -788 kJ/mol

Thus an anion bond does not form during formation of cation and anion but bond is formed when cation and anion combine to give a cystal.

Crystal Energy or Lattice Energy.

Amount of energy released when 1 mole of cation and anion are arrange in crystal lattice to form a crystal energy lattice energy.                                                                                                   

 Properties of Ionic Compound
1) Ionic compound are crystalline solids.
2) They have high melting point.
3) They have no molecules and are represented by emprical formula.
4) They have indefinite growth.
5) They are generally soluble in water.
6) They are not conductor of electricity in solid state but good conductor in solution form or molten state are called electrolytic conductors.

2) Covalent Bond:

Bond form by mutual sharing of electron between two atom s is called covalent bond.

Explanation:
Covalent bond is formed between two non metal atoms.Unpaired electron in the valance shell of atoms take part in covalent bond formation.In a covalent bond both the atoms of bond share electron to form bond.Electron pair of bond is called share pair or bond pair and it attracted by nuclei of both the atoms of a bond and is counted in both atoms.Thus in a covalent bond atoms acquire noble gas electronic configuration in the valance shell by the sharing of electrons.Covalent bond is represented by a solid line(----).This line represents shared pair of electrons.

H + H -------> H---H

Typs of Covalent Bond

There are three types of covalent bond.

1)Single Covalent Bond
Bond form by sharing of one pair of electrons between two atoms is called single covalent bond.A single covalent bond is formed if each atom of the bond shares one electron.

2)  Double Covalent Bond
Bond formed by sharing of three pair of electrons between two atoms is called double covalent bond.A double covalent bond id formed if each atom of the bond shares two electrons.

3)  Triple Covalent Bond
Bond formed by sharing of three pair of electrons between two atoms is called triple covalent bond.A triple covalent bond is formed if each atom of the bond share three electrons.

Properties Of Covalent Compound:
Covalent compounds are generally gasses and liquid.They exist in a molecules and are reprented by molecular formula.They are generally insoluble in water bur soluble in oganic solvent like sprit , benzene, ether etc.They are generally non conductors or bad conductors of electricity.

3)Co-ordinate Covalent Bond oR Dative Covalent Bond
Bond in which shared pair of electrons is denoted by one atom and accepted by other atom is called co-ordinate covalent bond or dative covalent bond.

Explanation
Atom of group IIIA like Al do not complete octet in valane shell after using all electrons of valance shell in bond formation.On the other hand atoms of group VA , VIA , VIIA like N , P , O , S , F , Cl , Br etc have lone pair of electrons in their valance shell after bond formation. A new bond is formed between two such atoms in which one atom has incomplete  octet and other which has lone pair of electrons.Atoms with lone pair donates its lone pai in sharing and the atom with incomplete octet accept that lone pair  to form bond called co-ordinate bond.