Chapter 2: Basic Chemistry – Study Guide (Sections 2.1–2.4)

Chapter 2: Basic Chemistry

2.1 Basic Atomic Structure

This section introduces the fundamental building blocks of matter and their relevance to anatomy and physiology.

• Atom: The smallest unit of an element that retains the properties of that element. Atoms consist of a nucleus (containing protons and neutrons) and electrons orbiting the nucleus.

• Proton: A positively charged particle found in the nucleus of an atom.

• Neutron: An uncharged particle found in the nucleus of an atom.

• Electron: A negatively charged particle that orbits the nucleus in energy shells.

• Element: A pure substance made of only one kind of atom (e.g., Oxygen, Carbon).

• Compound: A substance formed from two or more different elements chemically combined in fixed proportions (e.g., H2O).

• Molecule: Two or more atoms bonded together (can be the same or different elements).

• Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Valence Number: The number of electrons in the outermost shell, determining chemical reactivity.

• Electrolyte: A substance that dissociates into ions in solution and conducts electricity (e.g., NaCl in water).

Example: Carbon-14 is an isotope of carbon used in medical imaging and dating of biological materials.

2.2 Medical Uses of Isotopes

• Radioactive isotopes are used in diagnostic imaging (e.g., Technetium-99m in SPECT scans).

• Therapeutic uses include treatment of cancer (e.g., Iodine-131 for thyroid disorders).

2.3 Major Elements of the Body

The human body is primarily composed of a few key elements:

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Other important elements: Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg), Iron (Fe)

2.4 Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds.

• Ionic Bond: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other. Example: NaCl (sodium chloride)

• Polar Covalent Bond: Electrons are shared unequally between atoms, creating partial charges. Example: H2O (water)

• Nonpolar Covalent Bond: Electrons are shared equally between atoms. Example: O2 (oxygen gas)

• Hydrogen Bond: A weak attraction between a hydrogen atom (already covalently bonded to another atom) and an electronegative atom (like oxygen or nitrogen) in another molecule. Example: Between water molecules

Bond Strength:

• Strongest: Covalent bonds

• Weakest: Hydrogen bonds

2.5 Types of Chemical Reactions

• Synthesis Reaction: Two or more substances combine to form a more complex product. $A + B \rightarrow AB$

• Decomposition Reaction: A complex molecule breaks down into simpler substances. $AB \rightarrow A + B$

• Exchange Reaction: Parts of two molecules are exchanged to form two new compounds. $AB + CD \rightarrow AD + CB$

• Reversible Reaction: The reaction can proceed in both directions. $A + B \rightleftharpoons AB$

2.6 Enzymes

• Enzyme: A biological catalyst that speeds up chemical reactions without being consumed.

• Role in Chemical Reactions: Enzymes lower the activation energy required for reactions, increasing reaction rates.

• Components of Enzymes:

  • Apoenzyme: The protein portion

  • Cofactor: Non-protein component (may be a metal ion or coenzyme)

  • Active Site: The region where the substrate binds and the reaction occurs

Example: Amylase is an enzyme that catalyzes the breakdown of starch into sugars.

2.7 Properties and Functions of Water

• Excellent solvent for ionic and polar substances

• High heat capacity helps regulate body temperature

• Participates in chemical reactions (hydrolysis and dehydration synthesis)

• Provides cushioning and lubrication (e.g., cerebrospinal fluid, synovial fluid)

2.8 The pH Scale

The pH scale measures the concentration of hydrogen ions (H+) in a solution, indicating its acidity or alkalinity.

• pH Scale: Ranges from 0 (most acidic) to 14 (most basic); 7 is neutral.

• Acid: Substance that releases H+ ions in solution (pH < 7).

• Base: Substance that accepts H+ ions or releases OH- ions (pH > 7).

Equation:

$pH = -\log_{10}[H^+]$

2.9 pH of Body Fluids

Body Fluid	Normal pH Range
Blood	7.35 – 7.45
Gastric Juice	1.5 – 3.5
Urine	4.5 – 8.0
Saliva	6.35 – 6.85
Bile	7.6 – 8.6
Pancreatic Juice	7.5 – 8.8

Additional info: Table values inferred from standard physiology references.

2.10 Buffer Systems and Blood pH

• Buffer System: A solution that resists changes in pH when acids or bases are added.

• Primary Buffer System in Blood: The bicarbonate buffer system.

• How Buffers Work: Buffers can absorb excess H+ or OH- to maintain pH stability.

Example: The bicarbonate buffer system:

$CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$

• If blood becomes too acidic, bicarbonate (HCO3-) binds excess H+ to form carbonic acid (H2CO3), which can be converted to CO2 and exhaled.

• If blood becomes too basic, carbonic acid dissociates to release H+, lowering pH.

Other Buffer Systems: Phosphate buffer system, protein buffer system (e.g., hemoglobin in red blood cells).