Lecture Notes: Atoms, Molecules, and Water

Overview

• Focus on atoms and molecules.
• Detailed discussion on water due to its importance in anatomy and physiology.
• Understanding these concepts aids comprehension of cell functions.

Atoms and Atomic Theory

• Atomic Theory of Matter: Matter is composed of atoms.
• Subatomic Particles:
  • Protons: Charge +1
  • Neutrons: Neutral charge (0)
  • Electrons: Charge -1
• Atom Structure:
  • Example: Hydrogen atom.
  • Nucleus contains protons and neutrons.
  • Electron cloud surrounds the nucleus.

Molecules

• Definition: Two or more atoms bonded together.
• Bonding and Electrons:
  • Electrons play a key role in bonding.
  • Example: Hydrogen molecule (H₂) involves electron sharing.
• Chemical Shorthand:
  • Subscripts indicate the number of each atom in a molecule (e.g., H₂O, CO₂).

Water Molecule

• Composition: Two hydrogen atoms and one oxygen atom (H₂O).
• Polar Covalent Bonds:
  • Bonds formed by unequal sharing of electrons.
  • Electrons spend more time around oxygen, creating a partial negative charge.
  • Hydrogen atoms have a partial positive charge.
• Polarity:
  • Molecules with charged regions are polar; water is a polar molecule.

Types of Bonds

• Polar Covalent Bonds: Hold atoms together within a molecule.
• Hydrogen Bonds:
  • Occur between molecules, particularly polar molecules like water.
  • Involve attraction between partial charges of different molecules.
  • Crucial in biology due to the high number of bonds in substances like water.

Importance of Water

• Body Composition: 60-70% of body weight is water.
  • Found inside cells (intracellular) and outside cells (extracellular).
• Life-Supporting Properties:
  • Moderates temperature via heat capacity.
  • Lubricates joints and membranes.
  • Acts as a solvent and is involved in chemical reactions.

Heat Capacity and Evaporation

• Process:
  • Heat applied to water breaks hydrogen bonds, allowing evaporation.
  • This process cools the body as heat is transferred from the body to water molecules.

Water as a Solvent

• Polar Solvent: Dissolves charged or polar substances.
  • Examples: Salt (NaCl) dissolves as water molecules orient based on charge.
• Like Dissolves Like:
  • Polar molecules dissolve in polar solvents (e.g., water).
  • Non-polar molecules dissolve in non-polar solvents (e.g., oil).

Electrolytes

• Definition: Charged particles in fluid.
• Distribution:
  • Sodium ions: More outside cells.
  • Potassium ions: More inside cells.
  • Chloride ions: More outside cells.
  • Proteins: More inside cells.

Hydrophilic vs. Hydrophobic

• Hydrophilic: Water-loving, typically polar or charged (e.g., sugars, ions).
• Hydrophobic: Water-fearing, typically non-polar (e.g., oils, fats).
• Continuum: Molecules can range between being hydrophilic and hydrophobic.

Membrane Transport

• Barrier Passage:
  • Hydrophilic (polar) molecules cannot pass through hydrophobic barriers without assistance.
  • Hydrophobic (non-polar) molecules can pass through hydrophobic barriers.
• Cell Membranes:
  • Separates intracellular from extracellular fluid.
  • Allows selective passage based on polarity.

Review Questions

• Water's Role:
  • Found mostly in intracellular fluid.
  • Hydrogen bonds facilitate evaporation and cooling.
• Lubrication Examples:
  • Membranes around heart and joints.
• Dissolution and Polarity:
  • Verify understanding of which substances dissolve in which solvents based on their polarity.

Reminder:

• Understand key differences between hydrophilic and hydrophobic interactions.
• Know the distribution of electrolytes for understanding physiological processes.