Chemistry Foundations for Human Physiology: Atoms, Molecules, and Chemical Bonds

Chemistry Review for Human Physiology

Introduction

Understanding the basic principles of chemistry is essential for studying human physiology. Atoms, molecules, and chemical bonds form the foundation for the structure and function of cells, tissues, and organ systems in the human body.

Basic Chemical Concepts

States and Properties of Matter

• Matter is anything that occupies space and has mass. It exists in three primary states: solid, liquid, and gas.

• Mass is a measure of how much matter is present in a substance.

Atoms and Elements

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

• Element: A pure substance consisting of only one type of atom. Each element is defined by its number of protons.

• Molecule: Two or more atoms chemically bonded together (e.g., O2, H2O).

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

• Mixture: A combination of two or more substances that are not chemically bonded (e.g., air, saltwater).

Levels of Biological Organization

• Atoms combine to form molecules.

• Molecules form organelles (specialized structures within cells).

• Cells are the basic unit of life, composed of organelles.

• Tissues are groups of similar cells performing a common function.

• Organs consist of different types of tissues working together.

• Organ systems are groups of organs that perform related functions.

Structure of the Atom

Subatomic Particles

• Protons (p+): Positively charged particles located in the nucleus. The number of protons defines the atomic number and the element.

• Neutrons (n): Neutral particles (no charge) also found in the nucleus. The number of neutrons can vary, resulting in different isotopes of an element.

• Electrons (e-): Negatively charged particles that orbit the nucleus in energy levels (shells).

Atomic Number and Mass

• Atomic Number: The number of protons in an atom's nucleus.

• Atomic Mass: The sum of protons and neutrons in the nucleus.

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

Electron Shells and Stability

• Electrons are arranged in energy levels (shells) around the nucleus.

• The first shell holds up to 2 electrons; the second and third shells can hold up to 8 electrons each.

• Atoms are most stable when their outermost shell is full (the octet rule).

• Atoms may gain, lose, or share electrons to achieve a full outer shell, resulting in chemical bonding.

Chemical Bonds

Types of Chemical Bonds

• Ionic Bonds: Formed when electrons are transferred from one atom to another, creating charged ions that attract each other (e.g., NaCl).

• Covalent Bonds: Formed when two atoms share one or more pairs of electrons. Covalent bonds can be:

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

  • Polar Covalent: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

• Hydrogen Bonds: Weak attractions between the partial positive charge of a hydrogen atom and the partial negative charge of another atom (often oxygen or nitrogen). Important in water and biological molecules like DNA.

Examples of Chemical Bonds

• Water (H2O): Polar covalent bonds between hydrogen and oxygen; hydrogen bonds between water molecules.

• Sodium Chloride (NaCl): Ionic bond between sodium (Na+) and chloride (Cl-).

• Carbon Dioxide (CO2): Nonpolar covalent bonds between carbon and oxygen.

Chemical Formulas and Reactions

Chemical Formulas

• Use symbols to represent elements and subscripts to indicate the number of atoms (e.g., H2O, CO2).

Chemical Reactions

• Chemical reactions involve the formation, rearrangement, or breaking of chemical bonds.

• General format: Reactants → Products

• Law of Conservation of Mass: Matter is neither created nor destroyed in a chemical reaction.

• Reactions can be reversible.

Types of Chemical Reactions

• Synthesis (Anabolic) Reactions: Two or more simple substances combine to form a more complex substance. Example: $A + B \rightarrow AB$

• Decomposition (Catabolic) Reactions: A complex substance breaks down into two or more simpler substances. Example: $AB \rightarrow A + B$

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

Organic vs. Inorganic Molecules

• Organic Molecules: Contain carbon-carbon (C-C) or carbon-hydrogen (C-H) covalent bonds. Examples: glucose, proteins, lipids.

• Inorganic Molecules: Generally do not contain C-C or C-H bonds. Examples: water (H2O), carbon dioxide (CO2), salts.

Importance of Water in Physiology

• Water is the universal solvent in biological systems, facilitating chemical reactions and transport of substances.

• Its polarity allows it to dissolve many ionic and polar substances.

• Hydrogen bonding gives water unique properties essential for life, such as high heat capacity and surface tension.

Summary Table: Types of Chemical Bonds

Bond Type	How Formed	Example	Relative Strength
Ionic	Transfer of electrons; attraction between ions	NaCl	Strong (in dry state)
Covalent (Nonpolar)	Equal sharing of electrons	O2	Very strong
Covalent (Polar)	Unequal sharing of electrons	H2O	Very strong
Hydrogen	Attraction between partial charges	Between water molecules	Weak (individually)

Key Terms and Definitions

• Atom: Smallest unit of an element.

• Element: Substance made of only one kind of atom.

• Molecule: Two or more atoms bonded together.

• Compound: Molecule composed of atoms of different elements.

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

• Ionic Bond: Bond formed by transfer of electrons.

• Covalent Bond: Bond formed by sharing electrons.

• Hydrogen Bond: Weak bond between polar molecules.

• Organic Molecule: Contains C-C or C-H bonds.

• Inorganic Molecule: Lacks C-C or C-H bonds.

Additional info: Some explanations and examples have been expanded for clarity and completeness, as is standard in academic study guides.