Compounds & Bonding

Definitions of Compounds and Molecules

• Compounds:
  • A compound is formed when two or more elements are combined chemically.
  • The properties of a compound can be significantly different from the individual properties of the elements that comprise it.
• Molecules:
  • A molecule is formed when more than one atom is bonded together.
• Structural Analogy and Hierarchy:
  • Atoms join together to build molecules.
  • Elements combine to form compounds.
  • An atom is the basic building unit of an element, just as a molecule is the fundamental unit of a compound.

Chemical Formulas and Bond Formation

• Chemical Formulas:
  • A chemical formula uses element symbols and subscript numbers to depict the exact proportion of each atom in a molecule.
  • Example: Carbon Dioxide ($CO_2$):
    • $C$ represents a Carbon atom.
    • $O$ represents an Oxygen atom.
    • The subscript $2$ specifies that there are $2$ oxygen atoms bound to the single carbon atom.
• Mechanism of Bonding:
  • Bonds hold individual atoms together to form molecules.
  • Bonds are formed by the interaction of electrons present in the outermost energy level of an atom, known as valence electrons.

Types of Chemical Bonds

• Ionic Bonds:
  • Description: Strong attractions formed through ionic interactions between atoms.
  • Strength: Strong bond.
• Covalent Bonds:
  • Description: Bonds formed when electrons are shared between atoms, attracting both involved nuclei.
  • Strength: Strong bond.
• Hydrogen Bonds:
  • Description: Intermolecular or atomic attractions where electrons are not shared.
  • Strength: Weak attraction compared to ionic or covalent bonds.

Practical Examples and Summary

• Chemical Structure of Water:
  • Water molecules consist of $1$ oxygen atom and $2$ hydrogen atoms.
  • The chemical formula for water is $H_2O$.
  • Because the hydrogen and oxygen atoms within a water molecule share electrons, they are linked by covalent bonds.
• Key Conceptual Summary:
  • Molecules make up compounds, which are distinct elements joined together by bonds.
  • Ionic and covalent bonds hold atoms together tightly, whereas hydrogen bonds represent a weak attraction.