SSS 1: CHEMICAL COMBINATION (BONDING)

Chemical bond

Chemical bonding is the formation of a chemical bond between two or more atoms to hold them together as a stable molecule resulting in a chemical compound.

Chemical bond is the force of attraction that holds atoms or ions together in a molecule or compound.

      When atoms bond, they form molecules or compounds with lower energy and greater stability.

          Types of Chemical Bonding 

1. Electrovalent (Ionic) Bonding 

2. Covalent Bonding

3. Metallic bonding 

        Electrovalent (Ionic) Bonding

This is the type of bonding formed when one or more electrons are transferred from a metal atom to a non-metal atom.

       The metal becomes a positive ion (cation), while the non-metal becomes a negative ion (anion).

The electrostatic attraction between the oppositely charged ions forms the bond.

e.g. NaCl, MgO etc

Example : Formation of sodium chloride

(NaCl)

 Before bonding                  After bonding

       ₁₁Na    +     ₁₇Cl         →          NaCl

      2,8,1             2,8,7

      Properties of Ionic Compounds

1. High melting and boiling points

2. Conduct electricity when molten or dissolved in water

3. Usually soluble in water

4. Crystalline solids

                 Covalent Bonding 

This is the type of bonding that is formed when atoms of the same or different elements share electrons to achieve stability. The two atoms donate valence electrons to be shared. e.g. Hydrogen molecule (H₂), Chlorine molecule (Cl₂), Oxygen molecule (O₂), water molecule (H₂O)

            Types of covalent bonding 

There are two types of covalent bonding namely:

1. Ordinary covalent bonding

2. Coordinate covalent (Dative) bonding

             Ordinary covalent bonding

Examples:

Formation of a molecule of hydrogen gas

H  +  H → H₂

Formation of a molecule of chlorine gas

Cl + Cl →Cl₂

Formation of a molecule of water

             2H    +    O  →   H₂O

    

            Forms of Covalent Bonds

The different forms of covalent bonds are:

1. Single bond

One pair of shared electrons (H–H)

2. Double bond

Two pairs of shared electrons (O=O)

3. Triple bond

Three pairs of shared electrons (N≡N)

Properties of Covalent Compounds

1. They are usually gases or liquids with low melting and boiling points

2. They are poor conductors of electricity

3. They are often insoluble in water

   Coordinate covalent (Dative) Bonding 

     A coordinate covalent bond is a type of covalent bond in which both electrons shared in the bond are donated by one atom.

Example:

I. Formation of ammonium ion (NH₄⁺)

                 NH₃ + H⁺ → NH₄⁺

II. Formation of Hydronium Ion (H₃O⁺)

              H₂O + H⁺ → H₃O⁺

III. Formation of Ammonia Boron Trifluoride (NH₃→BF₃)

                      Metallic Bonding 

Metallic bond is found in metals, where positive metal ions are surrounded by a ‘sea’ of delocalized electrons.

    The attraction between the metal ions and free electrons holds the structure together.

      Properties of Metallic Bonding

1. Good conductors of heat and electricity

2. Malleable and ductile

3. Have high melting and boiling points

Differences Between Ionic and Covalent Bonds