Molecule

A molecule is an electrically neutral particle composed of two or more atoms held together by chemical covalent bonds (shared pairs of electrons) ¹.

Classification

• Diatomic / Polyatomic Elements: Composed of atoms of the same element bonded together (e.g., $\text{H}_2$, $\text{O}_2$, $\text{N}_2$, $\text{Cl}_2$, $\text{P}_4$).
• Molecular Compounds: Composed of atoms of two or more different elements chemically bonded (e.g., $\text{H}_2\text{O}$, $\text{CO}_2$, $\text{CH}_4$, $\text{NH}_3$).

    Hydrogen (H2)                Water (H2O)
   Element Molecule            Compound Molecule
      (H) : (H)                      (O)
                                    /   \
  Single Covalent Pair            (H)   (H)

Bonding and Physical Properties

Simple molecular substances exhibit distinct physical characteristics due to their dual-bonding nature ¹:

1. Intramolecular Bonds: Very strong covalent bonds holding atoms together inside each molecule.
2. Intermolecular Forces: Weak attractive forces between separate molecules.

Because little thermal energy is needed to separate molecules from one another, simple molecular substances have low melting and boiling points. Many are volatile liquids or gases under room conditions.

Related

• Atom - Individual chemical building block of molecules.
• Particle - Microscopic entity class encompassing molecules.
• Kinetic Particle Theory - Dynamic behavior of molecular particles in states of matter.
• Volatile - Substances with weak intermolecular attractions evaporating readily.
• Pure Substance - Chemical matter containing only one type of molecule or atom.
• Chemistry - Central science of chemical bonds and molecular behavior.