Chemical Bonds

Class Overview

  • Announcements: Pre-quizzes.
  • Required Reading: Chapters 2 and 3.1.
  • Main Goals:
    • Understand how atoms form molecules through chemical bonds and the properties of these bonds in building macromolecules.
    • Explore the chemical properties of water and their support for life.
    • Examine the essential contributions of carbon to the structure and variety of organic molecules.

Atomic Structure and Electron Arrangement

  • Electron Orbitals:
    • Electrons are arranged in orbitals surrounding the nucleus.
    • Orbitals represent the region or space around the nucleus with the highest probability of finding an electron.

Periodic Table

The periodic table organizes elements by atomic number and properties.

  • Key Features:
    • Elements are arranged in periods (rows) and groups (columns).
    • Each element is represented by its symbol, atomic number, and atomic mass.

Valence Electrons and Chemical Interactions

  • Valence Electrons:

    • Valence electrons are responsible for chemical interactions and bond formation.

  • Energy Considerations:

    • Energy is the capacity to cause change.
    • Potential energy is the energy that matter has because of its location or structure.
    • Different atoms have different potential energies and reactivity based on the distance of their electrons from the nucleus.

Chemical Bonds

  • Covalent Bonds:

    • Form when atoms share electrons.
    • Can be single, double, or triple bonds, depending on the number of shared electron pairs.

  • Electronegativity:

    • Differences in electronegativity between atoms lead to polar and nonpolar covalent bonds.

  • Brainstorm Activity:

    • Examples of covalent bonds that can form with major elements like Hydrogen, Oxygen, Nitrogen, and Carbon.

  • Octet Rule:

    • Atoms are most stable when their outer shell is filled, typically accepting 8 electrons.
    • Valence: Hydrogen (valence = 1), Oxygen (valence = 2), Nitrogen (valence = 3), Carbon (valence = 4).

  • Ionic Bonds:

    • Ions are formed when atoms gain or lose electrons.
    • An ionic bond is an attraction between a positively charged ion (cation) and a negatively charged ion (anion).
    • Example: Formation of Sodium Chloride (NaCl) from Sodium (Na) and Chlorine (Cl).

Intermolecular Forces

  • Hydrogen Bonds and Van Der Waals Forces:
    • Occur within and between molecules.
    • Classified as "weak" but are essential to biology.

Intermolecular vs. Intramolecular Forces

  • Intermolecular Forces:

    • Forces between molecules.
    • Weak to moderate in strength.
    • Examples: Dispersion forces, dipole-dipole interactions, hydrogen bonding, and ion-dipole interactions.
    • Zero attraction is only possible with ideal gases.

  • Intramolecular Forces:

    • Forces within molecules.
    • Strong to very strong.
    • Examples: Ionic bonds and covalent bonds.

  • Force Strengths (kJ/mol):

    • Dispersion: 0−20-2
    • Dipole-Dipole: 2−52-5
    • Hydrogen Bonding: 5−105-10
    • Ion-Dipole: 10−2010-20
    • Ion-Ion: 100−400100-400
    • Covalent Bonds: 400−1000400-1000