Ionic and Covalent Bonding: Properties and Structures

Ionic Bonds

Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions. Ionic bonds form when a metal and a non-metal exchange electrons. Positive ions are called cations and negative ions are called anions.

Ionic Substances

All ionic compounds form crystals that consist of lattices of positive and negative ions packed together in a regular way. The lattice is held together by the strong electrostatic attractions between the ions. Ionic compounds form crystals because the ions are arranged in a regular and repeated pattern, known as a Giant Ionic Lattice.

Properties of Ionic Substances

• High Melting and Boiling Points: Ionic bonds are very strong. Significant energy is required to break the strong electrostatic forces of attraction holding the lattice together.
• Electrical Conductivity: Ionic substances do not conduct electricity when solid because ions are in a fixed position. However, they do conduct when liquid (molten) or dissolved, as the ions are free to move.

Covalent Bonds

Covalent bonds are chemical bonds between two non-metal atoms (e.g., water). A covalent bond is formed when two atoms share electrons to complete their outer shell. They generally have low melting and boiling points.

Covalent Compounds

Most covalent substances do not conduct electricity because there are no free ions or electrons to carry a charge. Note: While some covalent structures are simple, others form giant networks.

Allotropes of Carbon

Allotropes are different forms of the same element. Carbon has several notable allotropes:

• Graphite: Each atom is covalently bonded to three others, forming rings of six atoms in layers. These layers are held together by weak forces. It is a Giant Covalent Structure that is soft, has a high melting/boiling point, and conducts electricity.
• Diamond: Each atom is covalently bonded to four others. It is a Giant Covalent Structure that is very hard, has a high melting/boiling point, and does not conduct electricity.
• Fullerene: A Simple Molecular Structure. It has lower melting/boiling points as only intermolecular forces are broken. It is not as hard as diamond and does not conduct electricity.