Chapter 4 Section 2: Covalent Bonding

Introduction

• Focus on covalent molecules, including Buckminster fullerene (buckyballs).
• Buckyballs consist of 60 carbon atoms covalently bonded into a sphere, resembling a soccer ball.
• Named after architect Buckminster Fuller, known for geodesic spheres.

Learning Objective

• Describe the formation of covalent bonds.

Covalent Bonds

• Definition: Form due to the attraction and sharing of a pair of electrons between two atoms.
  • Different from ionic bonds, which involve electrostatic attraction between charged particles.
  • No charged particles involved in covalent bonds.

Characteristics of Covalent Compounds

• Lower melting and boiling points compared to ionic compounds.
• Often liquids or gases at room temperature.
• Example: Water is a covalent compound.
• Weaker bonds than ionic compounds.
• Many are insoluble in water and poor conductors of electricity.
  • No ions or charged particles present.
  • Applies in solid, liquid, gas, or dissolved states.
  • The smallest unit is a molecule, not an ion.

Formation of Covalent Bonds

• Typically form between non-metal ions with similar electron affinities or ionization energies.
• Occur mainly in the non-metal part of the periodic table.
• Atoms share electrons equally.

Diagram Explanation

• Shows the relationship between distance between two nuclei (hydrogen atoms) and energy.
  • X-axis: Internuclear distance (picometers).
  • Y-axis: Energy (joules).
• Zero point chosen where nuclei are infinitely far apart.
  • No interaction and energy of the system is zero.

Energy and Interaction

• As atoms approach, energy decreases due to electron density distribution.
• Increased overlap of S orbitals leads to shared electrons and lower energy.
• Energy reaches a minimum at the most stable internuclear distance (bond length).
• Repulsive force between nuclei prevents further proximity.

Energy Changes and Bonds

• Formation of a bond releases energy (exothermic process).
• Breaking a bond requires energy (endothermic process).
• Important to track energy changes in physical and chemical changes.
  • Formation releases energy to surroundings.
  • Breaking bonds requires input of energy to return to an unbonded state.