Exhaustive Lecture Notes: Chemical Bonds, Reactions, Water Chemistry, and pH Homeostasis

Valence Electrons

The electrons residing in the outermost electron shell of an atom that participate directly in chemical bonding.

Octet Rule

The principle that atoms gain, lose, or share electrons to achieve a fully satisfied outer shell of $8$ electrons (or $2$ electrons for the first shell), rendering them chemically stable.

Ionic Bond

A chemical bond formed by the complete transfer of one or more valence electrons from one atom to another, creating oppositely charged ions that attract each other.

Cation

A positively charged ion formed when an atom donates one or more valence electrons (e.g., $Na^+$).

Anion

A negatively charged ion formed when an atom accepts one or more valence electrons (e.g., $Cl^-$).

Electrolyte

Any substance containing free ions that dissociates in aqueous solution and conducts electrical currents.

Covalent Bond

A chemical bond formed when participating atoms share pairs of valence electrons that orbit around both atomic nuclei.

Nonpolar Covalent Bond

A covalent bond in which shared electron pairs are shared equally between participating atomic nuclei.

Polar Covalent Bond

A covalent bond in which shared electron pairs are shared unequally due to differences in atomic electronegativity, creating partial positive ($\delta^+$) and partial negative ($\delta^-$) charges.

Hydrogen Bond

A weak intermolecular attraction formed between a partial positive charge ($\delta^+$) on a hydrogen atom of a polar molecule and a partial negative charge ($\delta^-$) on an electronegative atom of an adjacent polar molecule.

Cohesion

The physical property of identical polar molecules sticking together via hydrogen bonding, creating surface tension in water.

Surfactant

A lipid-protein complex produced by specialized lung cells that reduces water cohesion in pulmonary alveoli to prevent alveolar collapse.

Metabolism

The sum total of all chemical reactions occurring within a living organism.

Potential Energy

Stored energy derived from an object's spatial position or chemical molecular structure (such as chemical bonds).

Kinetic Energy

Energy actively expressed in physical motion.

Exergonic Reaction

A chemical reaction that net-releases energy into its surroundings as chemical bonds are broken.

Endergonic Reaction

A chemical reaction that requires a net input of energy to synthesize new chemical bonds.

Catabolism

Chemical pathways that break down complex molecules into smaller components; typically exergonic.

Anabolism

Chemical pathways that build larger, complex structures from smaller individual units; typically endergonic.

Activation Energy

The initial energy input required to destabilize existing chemical bonds and initiate a chemical reaction.

Enzyme

A biological catalyst made of protein that lowers the required activation energy of a chemical reaction without being consumed or altered.

Synthesis Reaction

An anabolic reaction ($A + B \rightarrow AB$) where simple reactants combine to form a complex product.

Decomposition Reaction

A catabolic reaction ($AB \rightarrow A + B$) where a complex reactant breaks down into simpler products.

Exchange Reaction

A chemical reaction ($AB + CD \rightarrow AD + CB$) in which reactant components switch partners to form new combinations.

Oxidation

The loss of electrons, hydrogen atoms, and associated energy from a substance during a chemical reaction.

Reduction

The gain of electrons, hydrogen atoms, and associated energy by a substance during a chemical reaction.

Dehydration Synthesis

An anabolic process in which two smaller molecules are joined covalently by removing a molecule of water.

Hydrolysis

A catabolic process in which complex molecules are broken into smaller units by adding a water molecule.

Hydrophilic

Polar molecules or charged ionic substances that readily interact with and dissolve in water.

Hydrophobic

Nonpolar, uncharged molecules (such as fats and oils) that do not dissolve in or mix with water.

Acid

A substance that dissociates in solution to release hydrogen ions ($H^+$); acts as a proton donor ($pH < 7.0$).

Base

A substance that dissociates in solution to release hydroxide ions ($OH^-$) or accept protons ($pH > 7.0$).

Salt

An inorganic ionic compound that dissociates in water into cations other than $H^+$ and anions other than $OH^-$ (e.g., $NaCl$).

Normal Blood pH Range

The physiological arterial blood $pH$ parameter maintained between $7.35$ and $7.45$.

Buffer

A chemical compound or system that reversibly binds or releases $H^+$ ions to prevent drastic shifts in $pH$.