Chemical Level of Organization

INTRODUCTION CHAPTER 2 The Chemical Level of Organization

CHAPTER OBJECTIVES

  • Upon completion, you should be able to:

    • Describe the fundamental composition of matter.

    • Identify the three subatomic particles.

    • Identify the four most abundant elements in the body.

    • Explain the relationship between an atom’s number of electrons and its relative stability.

    • Distinguish between ionic bonds, covalent bonds, and hydrogen bonds.

    • Explain how energy is invested, stored, and released via chemical reactions crucial to life.

    • Explain the importance of inorganic compounds (water, salts, acids, bases) contributing to life.

    • Compare and contrast the four vital classes of organic compounds (proteins, carbohydrates, lipids, nucleic acids) based on composition and functional importance to human life.

SMALL CHEMICAL ELEMENTS

  • The elemental components that form the human body are basic chemical elements, with nucleotide bases being the foundation of genetic code directing growth and maintenance from conception to old age.

    • Approximately three billion of these base pairs exist in human DNA.

    • Human chemistry includes organic molecules and biochemicals produced by the body, as well as essential earth-derived elements (e.g., phosphorus, carbon, sodium, calcium).

    • All elements crucial to life originated from stars and participate in forming both inorganic and organic compounds.

    • Example of significant compounds: water, glucose, proteins.

  • Human DNA is structured as a double helix organized into 46 chromosomes, illustrated by Figure 2.1.

2.1 ELEMENTS AND ATOMS: THE BUILDING BLOCKS OF MATTER

LEARNING OBJECTIVES

  • By the end of this section, you should be able to:

    • Discuss the relationships between matter, mass, elements, compounds, atoms, and subatomic particles.

    • Distinguish between atomic number and mass number.

    • Identify the key distinction between isotopes of the same element.

    • Explain how electrons occupy electron shells and their contributions to an atom’s stability.

MATTER

  • Defined as anything occupying space and having mass.

    • Mass: Amount of matter in an object, unchanged regardless of location (e.g., Earth vs. space).

    • Weight: Mass affected by gravitational pull, varying in different gravitational fields (e.g., a pound of cheese on Earth vs. ounces on the moon).

ELEMENTS AND COMPOUNDS

  • Composition of all matter: one or more of 92 fundamental substances known as elements.

    • An element: A pure substance that cannot be created or broken down by ordinary chemical means.

    • Elements essential for life include oxygen (O), carbon (C), hydrogen (H), nitrogen (N), among others.

  • Elements combine to form compounds through chemical bonds.

    • A compound: Composed of two or more elements joined by bonds.

    • Example: Glucose (C6H12O6) consists of carbon, hydrogen, and oxygen in fixed ratios (6C, 12H, 6O).

ATOMS AND SUBATOMIC PARTICLES

  • An atom: The smallest quantity of an element retaining its unique properties.

  • Atoms consist of subatomic particles:

    • Protons: Positively charged particles determining the atomic number of an element; located in the nucleus.

    • Neutrons: Neutral particles found in the nucleus, contributing to mass.

    • Electrons: Negatively charged particles orbiting the nucleus, equal in number to protons in neutral atoms.

ATOMIC STRUCTURE AND ENERGY

  • Models of atoms:

    • Planetary model: Suggests electrons orbit the nucleus in fixed paths.

    • Electron cloud model: Electrons occupy a cloud-like space around the nucleus, not in fixed orbits.

  • Electrical charges:

    • Protons (p+) and electrons (e–) are equal in a neutral atom, balancing its overall charge.

ATOMIC NUMBER AND MASS NUMBER

  • Atomic number: Number of protons and identifies the element. Example: Carbon has an atomic number of 6.

  • Mass number: The total number of protons and neutrons in an atom, e.g., carbon’s mass number in its most common form is 12 (6 protons + 6 neutrons).

  • Isotopes: Variants of elements differing in neutron number. e.g., Carbon isotopes: 12C (6 protons, 6 neutrons), 13C (6 protons, 7 neutrons), 14C (6 protons, 8 neutrons).

THE PERIODIC TABLE

  • Elements organized by atomic number in the periodic table; columns indicate elements with similar properties (i.e., same number of valence electrons).

CHEMICAL BONDS
LEARNING OBJECTIVES

  • By the end of this section, you should be able to:

    • Explain the relationship between molecules and compounds.

    • Distinguish between ions, cations, and anions.

    • Identify the key differences between ionic and covalent bonds.

    • Distinguish between nonpolar and polar covalent bonds.

    • Explain how water molecules interact through hydrogen bonds.

TYPES OF CHEMICAL BONDS

  • Molecules: Stable grouping of two or more atoms held together by chemical bonds.

    • Same-element molecules: e.g. H2 (molecular hydrogen).

    • Different-element molecules: e.g. H2O (water), CH4 (methane).

  • Bonds are formed through different mechanisms:

    • Ionic bonds: Formed through attraction between oppositely charged ions (cations and anions).

    • Covalent bonds: Formed where atoms share electrons (stronger than ionic).

    • Types:

      • Nonpolar covalent bonds: Equal sharing of electrons; no charge regions.

      • Polar covalent bonds: Unequal sharing of electrons; partially charged regions.

    • Hydrogen bonds: Weak; occur between a hydrogen atom covalently bonded to an electronegative atom (commonly oxygen) and another electronegative atom.

      • Significant in water interactions and biological compounds.

CHEMICAL REACTIONS
LEARNING OBJECTIVES

  • By the end of this section, you should be able to:

    • Distinguish between kinetic and potential energy, and exergonic vs. endergonic chemical reactions.

    • Identify four forms of energy crucial in human functioning.

    • Describe three basic types of chemical reactions.

    • Identify factors influencing the rates of chemical reactions.

ENERGY IN CHEMICAL REACTIONS

  • Energy is crucial to chemical reactions, categorized into:

    • Kinetic energy: Energy of moving matter.

    • Potential energy: Stored energy, including chemical energy within molecular bond structures.

  • Types of reactions:

    • Exergonic: Release more energy than absorbed; e.g., catabolic breakdown of molecules.

    • Endergonic: Absorb more energy than released; require energy input.

  • Forms of energy:

    1. Mechanical

    2. Radiant

    3. Electrical

    4. Chemical (stored in bonds).

CHEMICAL REACTIONS AND THEIR PRINCIPLES

  • Chemical transformations involve reactants and products without loss of mass (law of conservation of mass).

  • Types of chemical reactions:

    • Synthesis: Join reactants, requiring energy.

    • Example: N + 3H → NH3 (ammonia), absorbing energy.

    • Decomposition: Breakdown of a compound, releasing energy.

    • Example: NH3 → N + 3H.

    • Exchange reactions: Both synthesis and decomposition occur.

FACTORS INFLUENCING CHEMICAL REACTION RATES

  • Critical to numerous body chemical reactions:

    • Reactants’ surface area and composition affect interaction speed.

    • Temperature: Higher temperatures enhance reaction rates by increasing particle movement.

    • Concentration and pressure affect the frequency of collisions.

    • Enzymes: Biological catalysts that speed reactions by lowering activation energy, allowing reactions to proceed at body temperature.

INORGANIC COMPOUNDS ESSENTIAL TO HUMAN FUNCTIONING
LEARNING OBJECTIVES

  • By the end of this section, identify:

    • Properties distinguishing inorganic and organic compounds.

    • Essential role of water in life and various bodily processes.

    • Functions of salts, acids, and bases.

    • Mechanisms regulating pH balance via buffers.

INORGANIC COMPOUNDS IN HUMAN CHEMISTRY

  • Inorganic compounds: Do not contain both carbon and hydrogen.

    • Water (H2O): Most abundant and essential to life ( 70% of human body weight).

      • Roles in lubrication, thermal regulation, transport, and cushioning.

    • Salts: Compounds that dissociate into ions besides H+ or OH– when dissolved; important for conducting electrical signals.

    • Acids: Substances that release H+ in solution (e.g., Hydrochloric acid).

    • Bases: Accept H+ or release OH–; help neutralize acids.

  • pH: A measure of acidity or alkalinity (normal blood pH: 7.35 - 7.45).

  • Buffers: Stabilize pH by neutralizing excess acids/bases (e.g., bicarbonate).

ORGANIC COMPOUNDS ESSENTIAL TO HUMAN FUNCTIONING
LEARNING OBJECTIVES

  • By the end of this section, identify:

    • Four major classes of organic compounds crucial in human health.

    • Carbon’s property for covalent bonding in organic structures.

    • Major function of carbohydrates and four types of lipids important in the body.

    • Structure/function of proteins and building blocks of nucleic acids (DNA, RNA, ATP).

  • Organic compounds: Contain carbon and hydrogen.

    • Carbohydrates: Composed of carbon, hydrogen, and oxygen.

    • Lipids: Diverse compounds mainly consisting of hydrocarbons; includes triglycerides, phospholipids, and steroids.

    • Proteins: Composed of amino acids; play roles in structure, transport, signaling, enzymes (which speed up reactions).

    • Nucleic Acids: DNA and RNA store and transmit genetic information, ATP fuels cellular activities.

CARBOHYDRATES

  • Include monosaccharides, disaccharides, and polysaccharides.

  • Monosaccharides: Simple sugars (e.g., glucose).

  • Disaccharides: Two sugars bonded (e.g., sucrose).

  • Polysaccharides: Multiple sugars (e.g., starch, glycogen, cellulose).

LIPIDS

  • Triglycerides: Made of glycerol and fatty acids; primary energizing lipids in the body.

    • Can be saturated or unsaturated.

  • Phospholipids: Form cell membranes; contain polar heads and nonpolar tails.

  • Steroids: Comprise four fused carbon rings; cholesterol is significant in cellular membranes and hormone production.

PROTEINS

  • Amino acids: 20 kinds forming proteins, linked by peptide bonds.

  • Structure includes primary, secondary, tertiary, and quaternary forms affecting function.

    • Enzymes: Catalyze biochemical reactions critical to all life processes.

NUCLEOTIDES AND NUCLEIC ACIDS

  • Nucleotides: Comprising phosphate groups, pentose sugars (deoxyribose/ribose), and nitrogen bases.

    • DNA: Stores genetic information

    • RNA: Transfers information necessary for protein synthesis.

    • ATP: Primary energy carrier in cells, utilized in various metabolic processes.