Introduction to chemical bonding - Types of chemical bonds

Types of chemical bond

Chemical bonding organic chemistry can be classified into

a)     Ionic Bonds

b)     Covalent bonds

c)     Coordinate bonds

d)     Metallic bonds

e)     Hydrogen bonds

(a)- Ionic bond: 

It is chemical bond formed between metals and nonmetals or chemical bond formed between electropositive elements and electronegative elements. For example, the formation of sodium chloride salt. It is an electrostatic attraction between positive and negative ions.

₁₇Cl   1s² 2s² 2p^{6 3s2} 3p⁵                  

₁₁Na    1s², 2s² 2p^6, 3s¹                                

The sodium loss one electron and become positive ion and chloride accept electron and become negative ion then electrostatic attraction between these two oppositely charged ions is formed.

          Na⁺ +   Cl^-                        NaCl (attraction between cation and anion)

 

Ionic bond is formed if the difference in electronegativity between the two atoms is greater than 2

 

Properties of Ionic compounds       

• Ionic compounds have high melting point.
• Ionic compounds are soluble in water

(b)- Covalent bond: 

It is chemical bond formed between formed between nonmetal and nonmetal. It is sharing of electrons between atoms with close electronegativity values

                            

                       (Share of electrons between carbon and hydrogen)

                            

  Types of covalent bond:

Covalent bond can be divided into two types

1.        Pure covalent bond (Non polar covalent bond): equal sharing of electrons

2.        Polar covalent bond: Unequal sharing of electrons

The type of the bond Ionic, pure covalent or polar covalent is determined according to the difference in electronegativity between the two atoms as follow:

a.     If the difference in electronegativity 0-0.3, then there will be equal sharing and the bond is Pure covalent bond

b.     If the difference in electronegativity 0.3-2, then there will be unequal sharing and the bond is Polar covalent bond

c.      If the difference in electronegativity is greater than 2, then the bond will be ionic bond.

 

Properties of covalent compounds   

• The covalent compounds have low melting point.
• The bond in the organic compounds is covalent bonds.
• Covalent compounds usually are insoluble in water but soluble in organic solvents

 

(c)- Coordinate bond: 

Coordinate bond formed between two atoms (or atom and molecule) in which one is donator and the other is acceptor. For example the bond between F^- and BF₃ where the F^- is considered the donor species because it has higher electron density (electron rich species), while BF₃ has empty orbital to which they can accept electrons (electron deficient) and also it is non octet compound (B atom is surrounded only by 6 electrons - three bond only).

The donating atom called donor(or Lewis base) and the receiving atom called acceptor(or Lewis acid)

 Order of strength of bonds

Ionic bond > Coordinate bond > Covalent bond

 

(d)- Metallic bond:

Metallic bonds is the bond formed between metal and metal

It is the force of attraction that holds the metal atoms together in a metallic lattice.

It results from the fact that the valence electrons in metals become delocalized.

The more the number of valence electrons the more stronger is the metallic bond formed, that is the metallic bond of metals of group 3 is more stronger than metals of group 2 and the later is stronger than group 1.

 

(e)- Hydrogen bond:

-         It is bond occurs between molecules that have hydrogen atom bonded to high electronegative atom (F, N, O).

-         As the electronegativity of the atom bonded to hydrogen increase the strength of hydrogen bond increase.

-         Types of hydrogen bonds:

(i)- Intermolecular hydrogen bond:

Ø It is hydrogen bond that occurs between two or more molecules of the same type.

Ø Compounds that can form intermolecular hydrogen bond have high boiling point.

Ø Examples hydrogen bond in alcohols and hydrogen bond in water

   

 

(ii)-Intramolecular hydrogen bond:

It is hydrogen bond that occur inside the same molecule

 

 Compounds that can form intramolecular hydrogen bond have low boiling point.

Example : the imtramolecular hydrogen bond in methyl salicyalte