How do atoms combine to form molecules and compounds?

Atoms combine to form molecules and compounds primarily by interacting through their outermost valence electrons. This process occurs because atoms tend to distribute their electrons and nuclei in arrangements that result in a lower total energy state than they would have individually.1

There are three primary ways atoms form bonds:

• Ionic bonds: Electrons are transferred from one atom to another. This creates positively and negatively charged ions, which are then held together by the electrostatic force of attraction.23
• Covalent bonds: Atoms share pairs of electrons. In simple models, these electrons are treated as being shared between two nuclei; more advanced molecular-orbital theory describes these electrons as being distributed across the entire molecule.23
• Metallic bonds: In metals, atoms release outer electrons that float freely, effectively creating a "sea" of electrons shared by all atoms in the material.2

Additionally, atoms and molecules can interact through weaker forces, such as polar attractions, hydrogen bonds, and van der Waals forces, which do not involve the direct exchange or sharing of electrons in the same manner as primary chemical bonds.2