Chemical Bonding - Ionic / Covalent Bonds

A chemical bond is a lasting attraction between atomsthat enables the formation of chemical compounds. The bond may result from the electrostatic force of attraction between atoms with opposite charges, or through the sharing of electrons as in the covalent bonds. 

Ionic bonding

Ionic bonding is a type of electrostatic interaction between atoms which have a large electronegativity difference. There is no precise value that distinguishes ionic from covalent bonding, but a difference of electronegativity of over 1.7 is likely to be ionic.

 Ionic bonding leads to separate positive and negative ions.

A typical feature of ionic bonds is that the species form into ionic crystals, in which no ion is specifically paired with any single other ion, in a specific directional bond. Rather, each species of ion is surrounded by ions of the opposite charge, and the spacing between it and each of the oppositely charged ions near it, is the same for all surrounding atoms of the same type. It is thus no longer possible to associate an ion with any specific other single ionized atom near it. 

Covalent bonding

Covalent bonding is a common type of bonding, in which two atoms share two valence electrons, one from each of the atoms.

In nonpolar covalent bonds, the electronegativity difference between the bonded atoms is small, typically 0 to 0.5.

A polar covalent bond is a covalent bond with a significant ionic character. This means that the two shared electrons are closer to one of the atoms than the other, creating an imbalance of charge. Such bonds occur between two atoms with moderately different electronegativities and the electronegativity difference between the two atoms in these bonds is 0.3 to 1.7.

Properties of Ionic, Covalent, and Polar Covalent Compounds