9 Class Chemical Bonding and Reactions SCIENCE STUDY NOTES part 2

Chemical Bonding and Reactions

Covalent Compound

Covalent bonds are the bonds which are formed due to the equal sharing of electrons between two atoms.  These chemistry notes are provided by Chemistry Notes Info Organization www.ChemistryNotesInfo.com , This type of bonds (i.e. covalent bonds) is formed in atoms which carry four or more than four electrons in outermost shell, generally sharing of electrons happen in two ways –

1.     Equal Sharing – Covalent Bond

2.     One Side Sharing – Coordinate Bond

Covalent Compounds

                                      Compound which are formed as a result of covalent bonding and containing covalent bonds are known as Covalent Compounds.

Example: Hydrogen, Chlorine, Oxygen, Water, Ethanol etc.

Types of Covalent Bonds

Covalent Bonds are of three types which are as follows-

1.     Single Covalent Bonds

2.     Double Covalent Bonds

3.     Triple Covalent Bonds

Single Covalent Bonds

                                      Bonds which are formed due to sharing of single pair of electrons between two atoms are called single covalent bond. It is represented by single line (-)

Example: Formation of H₂ molecule, Formation of Cl₂ molecule.

i.                   Formation of Hydrogen (H₂) molecule:

                                                         In the outermost shell of hydrogen atom, it have single electron, which it share with another hydrogen atom to acquire inert configuration of helium so single bond is formed between these two hydrogen atoms and this single covalent bond is represented by single line (-)

ii.                 Formation of Chlorine Molecule (Cl₂) :

In the outermost shell of chlorine atom, it have seven electrons, it share its one valence electron with another chlorine atom to form chlorine molecule by single covalent bond.

Double Covalent Bonds

                                      Bonds which are formed due to sharing of double pair of electrons between two atoms are called double covalent bond. It is represented by double line (=)

Example: Formation of O₂ molecule.

i.                   Formation of Oxygen (O₂) molecule:

                                                          In the outermost shell of oxygen atom, it have six electrons, it share its two valence electrons with another oxygen atom to form oxygen molecule by double covalent bond.

Triple Covalent Bonds

                                      Bonds which are formed due to sharing of triple pair of electrons between two atoms are called triple covalent bond. It is represented by triple lines

Example: Formation of N₂ molecule.

i.                   Formation of Nitrogen (N₂) molecule:

                                                          In the outermost shell of nitrogen atom, it have five electrons, it share its three valence electrons with another nitrogen atom to form nitrogen molecule by triple covalent bond.

Characteristics of covalent compounds

1.     Crystal Structure:

                              Crystal structure of covalent compounds is formed from atoms or molecules. Crystal of covalent compounds are divided in three parts as –

i.                   These are crystals of covalent compounds whose molecule are very small and these molecules are held together by vander waals forces.

Example: Sulphur, Iodine.

ii.                 These are crystals of covalent compounds whose molecule are very large due to combination of every atom with other atom by covalent bonds.

Example:  Diamond, Silica.

iii.              These are crystals of covalent compounds whose have separate layers.

Example: Graphite.

2.     Physical Nature:

      Due to weaker force of attraction between the molecules of the covalent compounds, maximum covalent compounds are gases or liquids but some covalent compounds exist as solid like Urea, Sugar, Glucose, and Naphthalene.

3.     Solubility:

                Covalent compounds are not soluble in polar solvents like water but are soluble in non-polar solvent like alcohol, ether, carbon tetra chloride.

4.     Melting Point and Boiling Point ( MP and BP) :

                Melting and boiling points of covalent compounds are very low because very less energy is required to overcome the weak force of attraction between the neutral molecules in the covalent compound. But Diamond and Graphite are exception because they have very high melting and boiling points.

5.     Conductivity:

                   Covalent compounds do not have ions so they do not conduct electricity but some polar covalent compounds conduct very less electricity.

Polar Covalent Bond

                                    In the covalent compound if one is the more is more electronegative than other atom, then shared pair of electrons is attracted towards more electronegative atom so it acquire or obtain some partial negative charge which is represented by delta negative (d-) and other atom acquire some partial positive charge which is represented by delta positive (d+) therefore polar bond is form, which is known as Polar covalent bond.

Example : Hydrogen Chloride Molecule.

In HCl molecule, Chlorine is more electronegative than Hydrogen so chlorine acquires partial negative charge and hydrogen acquire partial positive charge.

Characteristics of Polar Covalent Compounds

i.                   Polar covalent compounds are approximately 80% covalent and 20% ionic so they so characteristics of both covalent and ionic (or electrovalent) compounds.

ii.                 In solution forms, polar covalent compounds are good conductor of electricity. Example: HCl

iii.              As compared to pure non-polar covalent compounds and electrovalent compounds, the melting point and boiling point of polar covalent compound are higher.

     9th Class Chemical Bonding and Reactions Part 1
     9th Class Chemical Bonding and Reactions Part 3