What Is A Molecule?

Key Notes:

Definition of a Molecule:

  • A molecule is a group of two or more atoms bonded together. These atoms can be of the same or different elements.
  • Molecules are the smallest unit of a chemical compound that can exist independently while retaining the chemical properties of that compound.

Types of Molecules:

  • Diatomic molecules: Composed of two atoms, usually of the same element (e.g., oxygen (O₂), nitrogen (N₂)).
  • Polyatomic molecules: Composed of three or more atoms, which may be the same or different elements (e.g., water (H₂O), carbon dioxide (CO₂)).

Atoms in Molecules:

  • Molecules are made up of atoms that are held together by chemical bonds, which can be covalent, ionic, or metallic bonds.
  • Covalent bonds: Formed when two atoms share electrons.
  • Ionic bonds: Formed when one atom gives up electrons to another atom, creating positive and negative ions that attract each other.

Molecular Formula:

  • A molecular formula represents the number and types of atoms in a molecule (e.g., H₂O for water, CO₂ for carbon dioxide).
  • It does not show the arrangement of atoms, which would require a structural formula.

Importance of Molecules:

  • Molecules make up all matter, including solids, liquids, and gases.
  • Biological molecules like proteins, DNA, and carbohydrates are essential for life processes.
  • Chemical reactions involve the breaking and forming of bonds between molecules.

Molecule vs Atom:

  • An atom is the smallest unit of an element, while a molecule is a combination of atoms.
  • Atoms can exist independently (e.g., noble gases like helium, neon), but molecules need at least two atoms to exist.

Properties of Molecules:

  • The properties of a molecule (such as its size, shape, and polarity) depend on the types of atoms involved and how they are bonded together.
  • For example, water molecules are polar, which means they have a slight electrical charge difference, allowing them to form hydrogen bonds.

Examples of Molecules:

  • Water (H₂O): Composed of two hydrogen atoms and one oxygen atom.
  • Carbon dioxide (CO₂): Composed of one carbon atom and two oxygen atoms.
  • Oxygen (O₂): Composed of two oxygen atoms.
  • Methane (CH₄): Composed of one carbon atom and four hydrogen atoms.

Let’s practice!