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

Basic Chemistry

Key Definitions

This section introduces fundamental chemical concepts essential for understanding anatomy and physiology at the molecular level.

• Atom: The smallest unit of an element that retains the properties of that element. Atoms consist of protons, neutrons, and electrons.

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

• Neutron: A subatomic particle with no charge, also located in the nucleus.

• Electron: A negatively charged subatomic particle that orbits the nucleus.

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

• Compound: A substance formed when two or more different elements combine chemically (e.g., H2O).

• Molecule: Two or more atoms held together by chemical bonds (can be the same or different elements).

• Acid: A substance that releases hydrogen ions (H+) in solution; proton donor.

• Base: A substance that accepts hydrogen ions or releases hydroxide ions (OH-); proton acceptor.

• Ion: An atom or molecule with a net electric charge due to 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).

Medical Uses of Isotopes

Isotopes have important applications in medicine, particularly as tracers and in diagnostic imaging.

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

• Iodine-131 is used to diagnose and treat thyroid disorders.

• Carbon-14 is used in metabolic studies.

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)

Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds. The type of bond affects the properties of the substance.

• 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 an electronegative atom) and another electronegative atom. Example: Between water molecules.

Strength of Bonds:

• Strongest: Covalent bonds

• Intermediate: Ionic bonds (strong in solid state, weaker in solution)

• Weakest: Hydrogen bonds

Types of Chemical Reactions

Chemical reactions involve the making or breaking of bonds between atoms.

• Synthesis (Anabolic) Reactions: Two or more atoms/molecules combine to form a larger molecule. Example: $A + B \rightarrow AB$

• Decomposition (Catabolic) Reactions: A molecule is broken down into smaller components. Example: $AB \rightarrow A + B$

• Exchange (Displacement) Reactions: Parts of molecules are exchanged. Example: $AB + CD \rightarrow AD + CB$

• Reversible Reactions: Can proceed in both directions. Example: $A + B \rightleftharpoons AB$

Enzymes and Their Role

Enzymes are biological catalysts that speed up chemical reactions in the body without being consumed.

• Function: Lower the activation energy required for reactions.

• Components:

  • 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 catalyzes the breakdown of starch into sugars.

Functions of Water

Water is vital for life and has several key roles in the body:

• Solvent: Dissolves many substances for transport and reactions.

• Temperature Regulation: High heat capacity helps maintain body temperature.

• Chemical Reactivity: Participates in hydrolysis and dehydration reactions.

• Lubrication and Cushioning: Protects organs and joints.

The pH Scale

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

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

• Formula: $\text{pH} = -\log_{10}[H^+]$

• Body Fluid pH Values:

  • Blood: 7.35–7.45 (slightly basic)

  • Gastric Juice: 1.5–3.5 (acidic)

  • Urine: 4.5–8.0 (varies)

  • Saliva: 6.35–6.85

Buffer Systems and Blood pH

Buffers help maintain stable pH in body fluids, especially blood.

• Buffer: A substance that minimizes changes in pH by binding or releasing H+ ions.

• Primary Buffer System in Blood: Bicarbonate buffer system.

• Example of Buffer Action: If blood becomes too acidic, bicarbonate ions ($HCO_3^-$) bind excess H+ to form carbonic acid ($H_2CO_3$), which can then be converted to CO2 and exhaled.

Buffer System	Main Components	Location
Bicarbonate	$H_2CO_3 / HCO_3^-$	Blood plasma
Phosphate	$H_2PO_4^- / HPO_4^{2-}$	Intracellular fluid, kidneys
Protein	Hemoglobin, plasma proteins	Blood, cells

Summary: The bicarbonate buffer system is the primary mechanism for controlling blood pH, working in conjunction with respiratory and renal systems.