Overview
This lecture explains why and how chemical bonds form between atoms, describes the main types of bonds, and highlights how their properties relate to energy, polarity, and atomic structure.
Why Atoms Form Bonds
- Atoms bond to lower their total energy by balancing attractive and repulsive forces.
- The attractive force is due to electrons of one atom being drawn to the protons of another (electrostatic force).
- The ideal distance where attractive and repulsive forces balance is the bond length, representing minimum energy.
Types of Chemical Bonds
- Covalent bonds form when atoms share electrons, typically between non-metals or metalloids.
- If electrons are shared equally, the bond is a non-polar covalent bond (e.g., Cl2).
- If electrons are shared unequally due to different electronegativities, the bond is a polar covalent bond (e.g., H2O).
- Ionic bonds form from the transfer of electrons from a metal to a non-metal, producing positive and negative ions that attract.
Electronegativity and Polarity
- Electronegativity is the ability of an atom to attract shared electrons in a bond.
- Large differences in electronegativity create polar covalent or ionic bonds.
- Polarity refers to the separation of charge in a molecule due to uneven electron distribution.
Calculating Bond Energy
- Coulomb’s law calculates the energy in ionic bonds:
Energy = (2.31 × 10⁻¹⁹ J·nm) × (charge₁ × charge₂) / bond distance (in nm)
- Ionic bonds are highly polar due to complete separation of charge.
Properties of Ionic vs. Covalent Compounds
- Ionic compounds are usually crystalline solids, dissolve in water, and conduct electricity in solution.
- Covalent compounds can be gases, liquids, or softer solids, are often insoluble in water, and their solutions do not conduct electricity.
Key Terms & Definitions
- Bond length — the distance between two nuclei where energy is minimized.
- Covalent bond — a bond formed by sharing electrons between atoms.
- Electronegativity — an atom's ability to attract shared electrons.
- Polar covalent bond — a covalent bond with unequal electron sharing and partial charge separation.
- Non-polar covalent bond — a covalent bond with equal or nearly equal electron sharing.
- Ionic bond — a bond formed by the transfer of electrons, producing positive and negative ions.
- Polarity — separation of electrical charge within a molecule.
- Coulomb's law — formula used to calculate the energy between two ions.
Action Items / Next Steps
- Review a table of electronegativities for common elements.
- Prepare for an upcoming episode on molecular polarity.