Ionic Versus Covalent Chemical Bonds Explained

Ionic Versus Covalent Chemical Bonds

Ionic Bonds

The ionic bond forms between elements with very different electronegativities. This involves the transfer of electrons from the less electronegative element to the most electronegative one. This process forms respective positive ions (cations, which lose electrons) and negative ions (anions, which gain electrons).

This type of bond typically occurs between elements at opposite ends of the periodic table: specifically, between highly electronegative elements (nonmetals) and less electronegative elements (metals).

Properties of Ionic Compounds

1. High melting and boiling temperatures.
2. Solid at room temperature.
3. The crystal lattice is very stable, making it very difficult to break.
4. They are hard (scratch resistant). They do not conduct electricity in solid form because the ions in the crystal lattice are in fixed positions and cannot move freely to conduct current.
5. They are generally soluble in water. When dissolved, the ions are free to move and can conduct electricity. They also conduct electricity when melted, as ions are released from their fixed positions.

Covalent Bonds

The covalent bond exists between elements with high and very similar electronegativities. In these cases, neither atom is significantly more likely than the other to lose or gain electrons. The way the octet rule is satisfied is through the sharing of electrons between two atoms. Each shared pair of electrons forms a bond.

This type of binding occurs between highly electronegative elements (nonmetals). The shared electrons are located between the atoms that share them.

Properties of Covalent Compounds

1. Low melting temperatures. At room temperature, they exist as gases, volatile liquids, or solids with low melting points.
2. The boiling temperatures are also low.
3. They do not conduct electricity in any physical state because the bonding electrons are strongly localized and attracted by the nuclei of the sharing atoms.
4. They are very poor conductors of heat.
5. Most are poorly soluble in water. When dissolved, they do not form ions because the covalent bond is not broken, and therefore, they do not conduct electricity when dissolved.