Chemical Bonding Types and Molecular Structures Explained

Chemical Bonding and Matter Fundamentals

Octet Rule

The formation of compounds tends toward atoms gaining electrons to achieve 8 electrons in their outermost shell.

Molecules

Molecules are formed by a set of atoms. Generally, small molecules are called diatomic (having 2 atoms), or triatomic, etc. Molecules are formed by atoms of the same element or consist of different atoms.

Crystals (General Structure)

Crystals are formed by a variable number of atoms, ions, or molecules, usually large, arranged in a regular, multi-dimensional lattice structure.

Ionic Bond

An ionic bond forms between a metal and a non-metal. Atoms tend to gain or lose electrons to achieve a stable configuration:

• Metals tend to lose electrons to form positive ions (cations).
• Non-metals tend to gain electrons to form negative ions (anions).

Oppositely charged ions attract each other and are held together by electrical forces. When a very large number of positive ions interact with a large number of negative ions, an ionic crystal forms.

Properties:

• They are solid at ambient temperature and are tough.
• They are soluble in H₂O.
• They do not conduct electricity in the solid state because the ions are fixed in the crystal structure, but they do conduct when molten or dissolved.

Covalent Bonds

This union occurs between two atoms of non-metallic elements, involving electron sharing.

Types of Covalent Compounds and Properties

Molecular Substances:

• They are formed by molecules. The atoms within the molecules are tightly bound, but the forces between molecules are very weak.
• This explains why most of these substances are gases or volatile liquids at ambient temperature.
• They do not conduct heat or electricity and are poorly soluble in water.

Covalent Crystals:

• Unions occur in all directions, forming crystal lattices.
• They are solid, very hard, and have very elevated melting points.
• They do not conduct heat or electricity and are soluble in H₂O.

Metallic Bond

When positive ions produced by a metal share a cloud of electrons. The ions are packed closely, causing a three-dimensional network whose geometry depends on the size of the ions.

Properties:

• They are solid at ambient temperature (except mercury).
• They are good conductors of heat and electricity due to the existence of free electrons that can move within the network.
• They are malleable and ductile.
• They possess a metallic luster, but when exposed to air, they react by altering their appearance and properties due to the formation of oxides (noble metals like gold do not do this).

The Mole Concept

The mole is an amount of substance that contains as many elementary units as there are atoms in 12 grams of Carbon-12.