Overview
This lecture introduces the three main types of chemical bonds—non-polar covalent, polar covalent, and ionic—and explains how bonds form to minimize energy between atoms.
Why Atoms Form Bonds
- Atoms bond to achieve the lowest possible energy by balancing attractive and repulsive forces.
- The electrostatic force draws electrons toward protons in neighboring atoms, creating attraction.
- Bonding reduces the stress (energy) of separated atoms by bringing them closer together.
- Too close, the nuclei repel; too far, attraction weakens—an ideal distance forms, called bond length.
Types of Chemical Bonds
- Covalent bonds form when atoms share electrons, often between non-metals or metalloids.
- Non-polar covalent bonds occur when electrons are shared equally between atoms with similar or identical electronegativities (e.g., Cl2).
- Polar covalent bonds occur when shared electrons are more attracted to one atom due to differences in electronegativity (e.g., H2O).
- Ionic bonds form when one atom transfers electrons to another, creating positive and negative ions (e.g., NaCl).
- Ionic bonds are extremely polar, as they involve full charge separation between ions.
Bond Properties and Energies
- Bond length is the distance at minimum energy between two nuclei.
- The bond energy can be calculated for ionic bonds using Coulomb's law:
Energy = (Q1 × Q2)/(radius) × 2.31 × 10⁻¹⁹ J•nm.
- Negative bond energy indicates a stable, attractive interaction.
Physical Properties of Compounds
- Ionic compounds are crystalline solids, usually soluble in water, and their solutions conduct electricity.
- Covalent compounds are often softer solids, liquids, or gases, and usually do not conduct electricity in solution.
Key Terms & Definitions
- Bond length — distance between nuclei at minimum energy.
- Electronegativity — measure of an atom’s ability to attract shared electrons.
- Covalent bond — shared pair of electrons between atoms.
- Non-polar covalent bond — equal sharing of electrons.
- Polar covalent bond — unequal sharing of electrons, causing partial charges.
- Ionic bond — bond formed by transfer of electrons, creating oppositely charged ions.
- Coulomb's law — formula calculating the energy between two charges at a certain distance.
- Polarity — separation of electrical charges leading to partial positive/negative areas in a molecule.
Action Items / Next Steps
- Review periodic table electronegativity values.
- Prepare for upcoming lectures focused on molecular polarity.