Lecture on Electrons, Electron Shells, and Chemical Bonds

Electron Shells and Valence Electrons

• Electron Shells:
  • First shell: Maximum of 2 electrons
  • Second shell: Maximum of 8 electrons
  • Third shell: Maximum of 8 electrons
• Examples:
  • Helium: 2 electrons (full outer shell)
  • Neon: 8 electrons (full outer shell)
  • Argon: 8 electrons (full outer shell)
• Valence Electrons:
  • Column 1 (e.g., Hydrogen, Lithium, Sodium): 1 valence electron
  • Column 2 (e.g., Beryllium, Magnesium, Calcium): 2 valence electrons
  • Column 3 (e.g., Boron, Aluminum, Gallium): 3 valence electrons
  • Column 4 (e.g., Carbon): 4 valence electrons
  • Column 5 (e.g., Nitrogen): 5 valence electrons
  • Column 6 (e.g., Oxygen): 6 valence electrons
  • Column 7 (e.g., Fluorine): 7 valence electrons
  • Column 8 (e.g., Neon): 8 valence electrons (full valence shell)

Inert Elements

• Elements in Column 8 are inert (non-reactive) due to full outer electron shells.

Chemical Bonds

Covalent Bonds

• Definition: Two atoms share electrons, forming a covalent bond.
• Molecule Formation: Two or more atoms bonded together.
• Hydrogen and Carbon Example:
  • Hydrogen (atomic number 1): 1 electron, needs 1 more for stability.
  • Carbon (atomic number 6): 6 electrons, 4 valence electrons, needs 4 more for stability.
• CH₄ (Methane): Carbon shares electrons with four Hydrogens (single covalent bonds).
• Covalent Bonds: Strong, energy input required to form and broken bonds release energy.

Importance in Biology

• Energy from food molecules is from breaking covalent bonds (e.g., glucose).
• Glucose (C₆H₁₂O₆): Chemical formula of glucose, covalent bonds store energy.
• ATP (Adenosine Triphosphate): Energy currency of the cell formed by breaking glucose bonds.

Types of Covalent Bonds

• Single Covalent Bond: One pair of electrons shared (e.g., Methane, CH₄).
• Double Covalent Bond: Two pairs of electrons shared (e.g., glucose, O₂).
• Triple Covalent Bond: Three pairs of electrons shared (e.g., N₂).

Energy Considerations

• Double bonds require more energy than single bonds, triple bonds require the most.
• No quadruple bonds due to energy constraints.

Polar and Non-polar Covalent Bonds

• Non-polar: Equal sharing of electrons.
• Polar: Unequal sharing of electrons.
• Further explanation will be covered in a subsequent lecture on hydrogen bonds.