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The Chemical Foundation of Life - Chapter 2

Introduction- Atoms are the building blocks of molecules in the universe, which include air, soil, water, rocks, and cells of all living organisms.

  • Important elements in living organisms include:

    • Carbon (C)

    • Hydrogen (H)

    • Nitrogen (N)

    • Oxygen (O)

    • Sulfur (S)

    • Phosphorus (P)

  • These elements form nucleic acids, proteins, carbohydrates, and lipids, which are fundamental components of living matter.

  • Understanding physics and chemistry is crucial for grasping biological processes:

    • Example: The flow of blood follows physics laws regulating fluid flow.

  • Chemical reactions, such as the breakdown of food into ATP, follow chemical laws.

  • Properties of water and hydrogen bond formation facilitate living processes.

  • Understanding acids and bases is vital for biological processes such as digestion.

2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks

Key Definitions

  • Matter: Any substance that occupies space and has mass.

  • Elements: Unique forms of matter with specific chemical and physical properties that cannot break down into smaller substances by ordinary reactions.

  • Total Elements: 118 elements known, with 98 occurring naturally; remaining are unstable and synthesized in laboratories.

  • Chemical Symbols: Elements are designated with unique symbols (e.g., C for carbon, Na for sodium).

  • Elements abundant in living organisms:

    • Oxygen (O): 65% in humans, 21% in the atmosphere, 46% in Earth's crust.

    • Carbon (C): 18% in humans, trace in atmosphere, trace in Earth's crust.

    • Hydrogen (H): 10% in humans, trace in atmosphere, 0.1% in Earth's crust.

    • Nitrogen (N): 3% in humans, 78% in atmosphere, trace in Earth's crust.

Structure of the Atom

  • Atom: Smallest unit of matter retaining element's properties; composed of:

    • Nucleus: Central part containing protons and neutrons.

    • Electrons: Orbit around the nucleus.

  • Atomic Mass Unit (amu): Established mass for protons/neutrons at approximately 1.67 \times 10^{-24} grams.

  • Charge of Subatomic Particles:

    • Protons: +1 charge, mass 1 amu, located in nucleus.

    • Neutrons: 0 charge, mass 1 amu, located in nucleus.

    • Electrons: -1 charge, weight 9.11 \times 10^{-28} grams, negligible mass; located in orbitals.

Atomic Number and Mass

  • Atomic Number: Number of protons in an atom; determines the element.

  • Mass Number: Total number of protons and neutrons; isotopes differ in neutron count but have the same atomic number.

  • Isotopes: Forms of an element with the same number of protons but different numbers of neutrons (e.g., Carbon-12 and Carbon-14).

Radioactive Isotopes

  • Radioisotopes: Unstable isotopes that emit radiation during decay (e.g., Carbon-14 decays to Nitrogen-14). Used in carbon dating for age estimation of organic materials.

    • Half-life: Time taken for half the quantity to decay; for Carbon-14, it is approximately 5,730 years.

The Periodic Table

  • Periodic Table: Organizes elements by increasing atomic number; elements are grouped by chemical properties.

  • Displays:

    • Atomic mass and number for each element.

Chemical Bonds and Molecules

  • Molecules: Formed by bonding between atoms; can be covalent or ionic.

    • Covalent Bonds: Sharing of electrons between atoms.

    • Ionic Bonds: Formed through electron transfer resulting in charged ions (cations lose electrons, anions gain).

    • Hydrogen Bonds: Weak attraction between polar molecules, crucial for water properties and macromolecule structures.

Electron Configuration and Stability

  • Electrons fill orbits in a specific manner leading to stable electron configurations (octet rule).

    • Valence Shell: Outermost shell; an element is more stable with a filled outer shell (usually eight electrons).

  • Elements interact through giving, taking, or sharing electrons to achieve stability.

Bonding Overview

  • Understanding that different groups of elements have varying tendencies for electron interactions helps predict chemical behavior.

2.2 Water

Importance of Water

  • Water is crucial for life, comprising 60-70% of the human body.

  • Properties attributed to water's polarity and hydrogen bonding include:

    • High heat capacity: Water absorbs/release heat slowly, stabilizing temperature.

    • High heat of vaporization: Significant energy needed for water to vaporize, allows organisms to cool through evaporation.

    • Solvent properties: Water dissolves polar and ionic substances, termed hydrophilic substances.

    • Cohesion and adhesion: Cohesion contributes to surface tension; adhesion enables capillary action necessary for plant water transport.

pH, Acids, and Buffers

  • pH: A measure of hydrogen ion concentration; scale ranges from 0 (acidic) to 14 (basic).

  • Buffers: Substances that help maintain pH by absorbing excess H+ or OH− to stabilize conditions for life.

2.3 Carbon

Role of Carbon

  • Carbon forms the backbone of macromolecules such as:

    • Proteins

    • Nucleic acids (RNA and DNA)

    • Carbohydrates

    • Lipids

  • Carbon has unique properties that allow it to bond covalently with many different elements, primarily forming chains and rings in organic molecules.

  • Hydrocarbons: Molecules of only carbon and hydrogen, which are used as fuels.

  • Functional Groups: Atoms or clusters of atoms, such as hydroxyl, carboxyl, amino, phosphate, etc., that attach to the carbon backbone and confer specific properties/functions on the macromolecules.

Isomers

  • Isomers: Molecules with the same formula but different structures (e.g., structural isomers, geometric isomers).

  • Enantiomers: Mirror-image structures important in biological systems (e.g., L-dopa and D-dopa).

Summary of Chapter 2

  • Life is built from atoms and molecules, governed by chemical properties and interactions.

  • Water is essential for maintaining life processes and biochemical reactions.

  • Carbon compounds form the foundation of macromolecules in living organisms.

Key Terms

  • Acid, Atom, Atomic Mass, Atomic Number, Balanced Chemical Equation, Base, Buffer, Calorie, Capillary Action, Cation, Chemical Bond, Chemical Reaction, Cohesion, Compound, Covalent Bond, Dissociation, Electron, Electron Configuration, Functional Group, Hydrocarbon, Isomer, Ionic Bond, Molecule, Neutron, pH, Solvent, and Valence Shell.

This comprehensive elaboration encapsulates the essential concepts and detailed explanations regarding the chemical foundation of life as described in Chapter 2 of the study material. Students can utilize these structured notes for an in-depth understanding of chemistry's role in biology, particularly in the functioning and interactions of living organisms.