Bio 107 - Chapter 2: Atoms and Molecules

Introduction to Matter

• Matter: Anything that takes up space and has mass.
• Mass vs. Weight: Mass is constant; weight varies with gravity.
• States of Matter: Solid, liquid, gas.

Elements and Atoms

• Elements: Substances that cannot be broken down into simpler substances by normal means.
  • 92 naturally occurring elements on Earth.
  • Most of the Earth’s mass is from oxygen, silicon, aluminum, and iron.
• CHNOPS: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur - 95% of human body weight.

Atomic Structure

• Atoms: Smallest unit of an element, maintaining its properties.
• Subatomic Particles:
  • Protons: Positive charge, found in nucleus.
  • Neutrons: No charge, found in nucleus.
  • Electrons: Negative charge, orbit nucleus in electron cloud.
• Atomic Mass: Sum of protons and neutrons.
• Atomic Number: Number of protons in an atom.

The Periodic Table

• Organization: Elements are arranged by atomic number.
  • Groups: Vertical columns.
  • Periods: Horizontal rows.
• Atomic Symbol: Letter(s) representing an element.

Isotopes

• Isotopes: Atoms of the same element with different numbers of neutrons.
  • Can become radioactive (e.g., Carbon-14).
  • Used in medical imaging like PET scans.

Electron Configuration

• Electrons and Orbitals: Electrons orbit the nucleus in energy levels (shells).
• Electron Shells: First shell holds 2 electrons, subsequent shells hold up to 8.
• Electron Distribution: Determines chemical reactivity and bonding.

Chemical Bonds

• Ionic Bonds: Transfer of electrons from one atom to another.
  • Example: Sodium chloride (table salt).
  • Formation leads to charged ions.
• Covalent Bonds: Sharing of electrons between atoms.
  • Can be polar or nonpolar depending on electron sharing.
• Hydrogen Bonds: Weak bonds important in biological systems, especially water.

Water and Its Properties

• Polar Molecule: Water molecules have partial positive and negative charges.
• Hydrogen Bonding: Causes water molecules to stick together (cohesive and adhesive properties).
• High Heat Capacity: Water absorbs heat without drastic temperature change.
• Solvent Properties: Water dissolves many substances (solution = solvent + solutes).
• Surface Tension: Water has a high surface tension, allowing some organisms to walk on it.
• Density: Ice is less dense than liquid water, causing it to float.

Acids, Bases, and pH

• Water Ionization: Forms hydrogen ions (H⁺) and hydroxide ions (OH⁻).
• pH Scale:
  • Acidic: High concentration of H⁺, low pH (0-6).
  • Neutral: pH 7.
  • Basic (Alkaline): High concentration of OH⁻, high pH (8-14).
• Buffers: Chemical systems that maintain pH balance in organisms (e.g., bicarbonate in blood).

Important Concepts

• Homeostasis: Maintaining stable internal conditions, including pH balance.
• Chemical Reactions: Energy changes involved in forming/breaking bonds.