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

Chapter 2: Chemistry and Measurements

Definitions of Key Terms

This section introduces fundamental chemical concepts and terminology essential for understanding matter and its interactions.

• Atom: The smallest unit of an element that retains the properties of that element.

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

• Neutron: A neutral subatomic particle found in the nucleus of an atom.

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

• Element: A pure substance consisting of only one type of atom.

• Compound: A substance formed when two or more elements are chemically bonded together.

• Molecule: Two or more atoms bonded together, representing the smallest unit of a compound.

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

• Base: A substance that releases hydroxide ions (OH-) or accepts hydrogen ions in solution.

• 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 of an atom, determining its bonding capacity.

• Electrolyte: A substance that produces ions when dissolved in water, conducting electricity.

Medical Uses of Isotopes

Isotopes are used in medicine for diagnosis and treatment due to their unique radioactive properties.

• Diagnostic Imaging: Technetium-99m is used in nuclear medicine scans.

• Treatment: Iodine-131 is used to treat thyroid disorders.

• Tracer Studies: Radioactive isotopes help track biochemical processes in the body.

Major Elements of the Human Body

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

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Calcium (Ca)

• Phosphorus (P)

These elements are essential for life and make up over 98% of the body's mass.

Types of 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 (e.g., NaCl).

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

• Nonpolar Covalent Bond: Electrons are shared equally between atoms (e.g., O2).

• Hydrogen Bond: A weak attraction between a hydrogen atom (in a polar molecule) and an electronegative atom (e.g., between water molecules).

Strength Comparison:

• Strongest: Ionic and covalent bonds (especially nonpolar covalent)

• Weakest: Hydrogen bonds

Molecular Examples:

• NaCl: Ionic bond

• H2O: Polar covalent bond

• O2: Nonpolar covalent bond

• Water molecules: Hydrogen bonds between molecules

Types of Chemical Reactions

Chemical reactions involve the transformation of substances through breaking and forming bonds.

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

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

• Exchange Reaction: Parts of two compounds are exchanged. Example: $AB + CD \rightarrow AD + CB$

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

Enzymes and Their Role in Chemical Reactions

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: Region where substrate binds and reaction occurs.

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

Functions of Water

Water is vital for life and has several important functions 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: Reduces friction in joints and tissues.

The pH Scale

The pH scale measures the acidity or alkalinity of a solution, ranging from 0 (most acidic) to 14 (most basic).

• Acidic: pH < 7

• Neutral: pH = 7

• Basic (Alkaline): pH > 7

Formula:

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

pH of Body Fluids

Body fluids have characteristic pH values essential for physiological function.

Fluid	Typical pH
Blood	7.35–7.45
Urine	4.6–8.0
Gastric Juice	1.0–3.0
Saliva	6.5–7.5
Bile	7.6–8.6

Additional info: Values inferred from standard physiology references.

Buffer Systems and Blood pH

Buffer systems help maintain stable pH in body fluids, especially blood.

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

• Example: The bicarbonate buffer system in blood.

• Primary Buffer System: Bicarbonate (HCO3-)/Carbonic Acid (H2CO3) system.

How Buffer Systems Work:

• When blood pH drops (more acidic), bicarbonate ions neutralize excess H+:

• $\text{HCO}_3^- + \text{H}^+ \rightarrow \text{H}_2\text{CO}_3$

• When blood pH rises (more basic), carbonic acid releases H+:

• $\text{H}_2\text{CO}_3 \rightarrow \text{HCO}_3^- + \text{H}^+$

Example: The bicarbonate buffer system maintains blood pH within the narrow range necessary for life.

Additional info: The phosphate and protein buffer systems also contribute, but bicarbonate is primary in blood.