Understanding Ionic and Covalent Chemical Bonding

Ionic Bonds

An ionic bond occurs when atoms of metallic elements (especially those located further to the left in the periodic table, groups 1, 2, and 3) meet with non-metallic atoms (elements on the right in the periodic table, especially groups 16 and 17). The electronegativity difference is greater than 1.7.

In this case, metal atoms donate electrons to nonmetal atoms, becoming positive and negative ions, respectively. These oppositely charged ions are attracted by strong electrical forces, binding them tightly and giving rise to an ionic compound. These electrical forces are called ionic bonds.

Properties of Ionic Compounds

• Solid at room temperature.
• High melting and boiling points.
• Good conductors when melted or dissolved in water.
• Brittle in solid state.
• Poor conductors of heat in solid state.
• Easily dissolve in water at room temperature.
• Three-dimensional structures (crystal lattices).

Covalent Bonds

Covalent bonds are the forces that hold together nonmetal atoms (elements located on the right of the periodic table, such as C, O, F, Cl). These atoms have many electrons in their outer level (valence electrons) and tend to gain electrons to acquire the stability of a noble gas electronic structure. Therefore, non-metallic atoms cannot transfer electrons to form ions of opposite signs.

In this case, the bond is formed by sharing a pair of electrons between two atoms, one from each atom. The shared electron pair is common to both atoms, allowing them to acquire a noble gas structure. This usually forms molecules: small groups of atoms linked by covalent bonds. The electronegativity difference is between 0 and 1.7.

Types of Covalent Bonds

• Polar Covalent: Forms when the electronegativity difference is greater than 0 but less than 1.7. This creates diatomic and polyatomic molecules (e.g., HCl).
• Coordinate (Dative) Covalent: Occurs when only one of the participating atoms provides the electrons. These are always polar (e.g., H₂SO₄ and HNO₃).
• Nonpolar Covalent: Formed by the union of atoms with the same electronegativity (difference = 0). This gives rise to homoatomic molecules (e.g., H₂, N₂, O₂).

Molecular Substances

Molecular substances consist of molecules linked to each other by intermolecular forces, which depend on molecular mass and density. They may exist as solids, liquids, or gases. They have lower melting and boiling points, are poor conductors of heat and electricity, and are soluble in water when polar, but insoluble when nonpolar. They are often soft and have low mechanical resistance (e.g., carbon dioxide, oxygen, water, and ethyl alcohol).

Network Covalent Substances

These substances form an indefinite number of units linked by covalent bonds. The structure consists of a large number of interconnected nuclei and electrons. They are characterized by existing only in the solid state, having extremely high melting and boiling points, being tough, and being insoluble. They do not conduct electricity (e.g., diamond, graphite, and quartz).