In-Depth Notes on The Chemical Foundation of Life

The Chemical Foundation of Life

• Fundamental Assumptions of Chemistry:
  • 1. All matter is composed of atoms.
  • 2. Atoms of a given element differ from those of other elements.
  • 3. Chemical compounds consist of atoms combined in specific ratios.
  • 4. Chemical reactions change only the way atoms are combined; the atoms themselves remain unchanged.

Elements and Body Weight

• Key elements in human body by percentage:
  • Oxygen: 65.0%
  • Carbon: 18.6%
  • Hydrogen: 9.7%
  • Nitrogen: 3.2%
  • Other elements like Calcium, Phosphorus, and Potassium contribute to lesser percentages.
• Together, these four elements make up 96.5% of total body weight.

Atomic Structure

• Atom: Smallest unit of matter with all chemical properties of an element.

  • Composed of two main regions:
  • Nucleus: Contains protons (positive charge) and neutrons (neutral).
  • Outermost region: Houses electrons (negative charge).

• Subatomic Particles:

  • Protons and neutrons have a mass close to 1 amu, electrons are 1836 times lighter than protons and neutrons.
  • Protons (+) and electrons (-) have equal charges, atoms are generally electrically neutral.

• Atomic Number (Z): Number of protons in the nucleus; defines the element.

• Mass Number (A): Total number of protons and neutrons in an atom.

Isotopes

• Isotopes: Atoms of the same element with different neutron numbers.
  • Example: Carbon-14 is used in dating fossils and tracing metabolic processes.
• Radioactive Isotopes: Decay and release energy; useful in medical diagnostics.

Periodic Table and Atomic Mass

• Elements organized by atomic mass and atomic number.
• Atomic Weight Calculation:
  • Average mass of an element's isotopes.
  • Formula: Atomic\,Weight = \sum (isotope\, abundance) \times (isotope\, mass)
• Different elements have unique positions based on their properties.

Electron Configuration

• Electrons are arranged in layers (shells) around the nucleus.
  • Higher energy levels can hold more electrons.
  • Each shell has subshells: s, p, d, and f.
• Valence Shell: Outermost shell influencing chemical bonding.
• Electron Configuration Rules:
  • Fill lowest energy orbitals first.
  • Each orbital can hold a maximum of 2 electrons.

Chemical Bonds

• Covalent Bonds: Atoms share electrons to achieve stable outer shells.

  • Example: Water (H2O) with two hydrogen atoms and one oxygen atom.
  • Polar Covalent Bonds: Unequal sharing of electrons leads to partial positive and negative charges.

• Ions: Charged atoms formed from gaining or losing electrons.

  • Cations: Positive ions that lose electrons.
  • Anions: Negative ions that gain electrons.

• Ionic Bonds: Electrostatic attractions between oppositely charged ions.

Properties of Water

• Water is critical for life and exhibits unique properties due to hydrogen bonding:

  • Cohesion: Water molecules stick to each other, leading to surface tension.
  • Adhesion: Water molecules stick to other surfaces, facilitating capillary action.
  • High specific heat: Water resists temperature change, stabilizing environments.
  • Solvent properties: Water dissolves ionic and polar substances.

• Hydrophobic vs Hydrophilic:

  • Hydrophilic substances have an affinity for water; hydrophobic substances do not.

Acids and Bases

• Acids: Increase H+ concentration in solution.
• Bases: Reduce H+ concentration in solution.
• pH Scale: Quantifies the acidity or basicity of a solution.
  • Neutral water has pH of 7.
  • Acidic solutions have a pH < 7; basic solutions have a pH > 7.

Importance of Carbon

• Carbon is the backbone of life, forming complex molecules through covalent bonds.
  • Carbon forms various structures: chains, branches, rings, and different isomers.
• Functional Groups: Distinctive groups responsible for the properties of organic molecules. Examples include hydroxyl, carboxyl, amino, and phosphate groups.

Summary

• Understanding the foundation of life involves grasping atomic theory, electron configurations, types of chemical bonds, and the unique properties of water and carbon compounds.
• These elements and interactions form the basis of biological systems and are crucial for the chemistry of life.