MOLECULES

 1.1.2 MOLECULES

A molecule is an electrically neutral group  of two or more atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their lack of electrical charge. However, in quantum physics, organic chemistry and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions.

In the kinetic theory of gases, the term molecule is often used for any gaseous particle regardless of its composition. According to this definition, noble gas atoms are considered molecules despite being composed of a single non-bonded atom.

• A molecule may be homonuclear, that is, it consists of atoms of a single chemical element, as with water (H2O).
• Atoms and complexes connected by Non-covalent bonds such as Hydrogen Bonds or Ionic Bonds are generally not considered single molecules
• Molecules as components of matter are common in organic substances( and therefore biochemistry).
• They also make up most of the oceans and atmosphere. However, the majority of Familiar Solid Substances on Earth, including most of the minerals that make up the Crust, Mantle, and Core of the Earth, Contain many Chemical Bonds, But are not made of identifiable molecules.
• Also, no typical molecule can be defined for ionic crystals (salts) and Covalent Crystals (Network Solid),although these are often composed of repeating unit cells that extend either in a plane (Suchas in Graphene) or three-dimensionally (Such as in Diamond. Quartz, or Sodium Chloride).
• The theme of Repeated Unit-Cellular-Structure also holds for most condensed phases with metallic bonding, which means that Solid metals are also not made of molecules.
• In glasses (Solids that exist in a vitreous disordered state), atoms may also be held together by chemical bonds without presence of any  definable molecule, but also without any of the regularity of repeating units that characterises crystals.

                                                    NEXT PAGE