Notes on Chemical Bonds

Introduction: Relationships and Bonds

• Humans, like chemicals, are all about bonds.
• Relationships vary: acquaintances, colleagues, friends, casual, committed, married.
• Different relationships have different requirements.
• Balance of distance in relationships is important. Too much distance can lead to disconnection; too little can lead to being overwhelmed.
• Atoms are similar to humans in that they form bonds, which require different types of energy and aim for low stress situations.

Why Atoms Form Bonds

• Atoms seek to reduce their overall energy.
• Achieve lowest energy by balancing attractive and repulsive forces.
• Atoms attract each other due to electrostatic force: opposites attract, like charges repel.
• When atoms are too close, their nuclei repel each other, increasing energy.

Bond Length

• The ideal distance where attractive and repulsive forces balance is called bond length.
• Example: Chlorine gas (Cl2), bond length = 0.00199 nanometers, energy minimum = -239 kJ/mol.

Types of Chemical Bonds

Covalent Bonds

• Formed when electrons are shared between atoms.
• Electrons spend most time between the nuclei of the bonded atoms.
• Electronegativity: strength of an atom's pull on shared electrons.
  • Example: Hydrogen (2.1) vs. Oxygen (3.5).
  • Unequal sharing leads to polarity.

Polar Covalent Bonds

• Electrons are attracted more to one atom, creating a slight negative charge on one end and a slight positive charge on the other (e.g., H2O).

Nonpolar Covalent Bonds

• Electrons are shared evenly (e.g., Cl2).
• Example of nearly equal electronegativity: Hydrogen (2.1) and Sulfur (2.5).

Ionic Bonds

• Formed by transfer of electrons from one atom to another (metal to nonmetal).
• Example: Sodium (Na) and Chloride (Cl).
• Atoms become ions: sodium becomes Na⁺ and chloride becomes Cl⁻.
• Ionic bonds are strong due to the attraction between opposite charges.
• Coulomb's Law: Used to calculate energy in ionic bonds.
  • Formula: Energy = (Product of charges) / (Distance)
  • Example Calculation: NaCl bond energy = -8.37 x 10^-19 joules.

Properties of Bonds

• Ionic Compounds:
  • Crystalline solids (e.g., table salt).
  • Generally soluble in water, conduct electricity when dissolved.
• Covalent Compounds:
  • Softer solids, liquids, or gases (e.g., Cl2).
  • Often not soluble in water, solutions do not conduct electricity.

Conclusion

• Chemical bonds form to minimize energy between atoms or ions:
  • Covalent bonds: share electrons (evenly or unevenly).
  • Ionic bonds: transfer of electrons.
• Understanding polarity is crucial for differentiating between bond types.

Acknowledgments

• Episode written by E.D. Gonzalez; edited by Blake de Pastino.
• Chemistry consultant: Dr. Heiko Langner.
• Filmed, edited, directed by Nicholas Jenkins; sound design by Michael Aranda; graphics by Thought Cafe.