CHEMICAL BOND- COVALENT BOND

CHEMICAL BOND-  COVALENT BOND

Atoms form a covalently bonded molecule by sharing 1, 2 or 3 pairs of valence electrons.

The larger the number of electron pairs shared between 2 atoms, the stronger the covalent bond.

  Covalent bond may form between 
                            atoms of the same element 
                                   OR
                     atoms of different elements.

Covalent bonds are the most common chemical bonds in the body 
 and the compounds that result from them form most of the bodys structure.



SINGLE COVALENT BOND

When 2 atoms share 1 electron pair.

eg

H-H


A nucleide of hydrogen forms, when 2 hydrogen atoms share their single valence electrons.

            -this allows both atoms to have a full valence shell at least part of the time.


DOUBLE COVALENT BOND

When 2 atoms share 2 pair of electrons

eg. oxygen molecule

oxygen=8
2,6

O=O  O2
2,4,2,2,4,2


TRIPLE COVALENT BOND 

When 2 atoms share 3 pairs of electrons

eg. nitrogen molecule

N =7
2,5

N ≡ N
2,2,3,3,2

STRUCTURAL FORMULA

Number of lines between the chemical symbols for 2 atoms indicates whether the bond is single (-)
                                              double (=)
                                            or triple (≡)   covalent bond.

eg.

H -H
O = O
N  ≡ N


COVALENT BONDS BETWEEN ATOMS OF DIFFERENT ELEMENTS

eg.  The gas methane CH4

    - contains covalent bond formed between the atoms of 2 different elements
1 Carbon  and 4 Hydrogen atoms

The valence shell of the carbon atom can hold 8 electrons , 
          but has only 4 of its own.

C-4; 2,2

The single electron shell of hydrogen atom can hold 2 electrons
         but each hydrogen atom has only one electron of its own.
H-1

A methane molecule contains 4 separate single covalent bonds.

Each hydrogen atom shares 1 pair of electron with carbon atom.

POLAR COVALENT BOND

The sharing of electrons between 2 atoms is un equal.

The nucleus of 1 atom attracts the shared electron more strongly than the nucleus of another atom

The resulting molecule has a partial negative charge near the atom that attracts electrons more strongly.

This atom has greater  ELECTRONEGATIVITY    - the POWER TO ATTRACT ELECTRONS TO ITSELF

At least 1 other atom in the molecule then will have a partial positive charge
     

SYMBOL FOR THE PARTIAL CHARGES

Lowercase Greek delta with a minus  δ− or plus sign δ+

eg.

Bond between hydrogen and oxygen  in a molecule of water

In this molecule

the nucleus of the oxygen atom attracts the electrons more strongly than the nucleus of hydrogen atoms, 
so the oxygen atom is said to have greater electronegativity.


NON POLAR COVALENT BONDS

2 atoms share the electrons equally 

1 atom doesnot attract the shared electrons more strongly than the other atom.

eg. CH4- Methane

The bonds between cabon and hydrogen atoms are non polar as 4 C-H bonds in a methane molecule.