Lecture Exam #2 Review: Water, Carbon, and Biological Macromolecules

Water Molecule ($H_2O$)

A polar molecule composed of two hydrogen atoms covalently bonded to a single electronegative oxygen atom.

Polar Molecule

A molecule characterized by an uneven distribution of electrical charges across different regions of its structure.

Polar Covalent Bond in Water

A covalent bond between oxygen and hydrogen where shared electrons are pulled closer to the more electronegative oxygen atom.

Electronegativity of Oxygen

The strong intrinsic tendency of an oxygen atom to attract shared bonding electrons toward itself.

Partial Negative Charge ($\delta^-$) in Water

The localized negative charge that develops on the oxygen atom of water due to its higher electronegativity.

Partial Positive Charge ($\delta^+$) in Water

The localized positive charge that develops on each hydrogen atom of water due to unequal electron sharing.

Molecular Dipole of Water

The permanent vector sum of individual bond dipoles resulting in distinct positive and negative poles in a water molecule.

Bent Shape of Water

The angular molecular geometry of water with an approximate $104.5^\circ$ bond angle that prevents dipole cancellation.

Charge Asymmetry in Water

The non-uniform spatial distribution of electron density between the oxygen region and hydrogen regions of water.

Water Polarity

The foundational chemical state of water having opposite electrical charges on opposite ends of its molecular framework.

Dipole-Dipole Interaction in Water

The electrostatic attraction occurring between opposite permanent dipole poles of adjacent polar water molecules.

Hydrogen Bonding

A noncovalent attraction between a partially positive hydrogen atom of one polar molecule and an electronegative atom of another.

Hydrogen Bonding in Water

The intermolecular attraction where the partially positive hydrogen of one water molecule binds to the partially negative oxygen of another.

Hydrogen Bond Donor in Water

The water molecule that provides the partially positive hydrogen atom participating in a hydrogen bond.

Hydrogen Bond Acceptor in Water

The electronegative oxygen atom of a water molecule that accepts a hydrogen bond via its nonbonding electron pairs.

Transient Nature of Water Hydrogen Bonds

The dynamic property whereby hydrogen bonds in liquid water continually break and reform within trillionths of a second.

Hydrogen Bonding Network

The interconnected, fluctuating dynamic mesh of hydrogen bonds that unites molecules in liquid water.

Four Hydrogen Bonds per Water Molecule

The theoretical maximum number of hydrogen bonds a single water molecule can form simultaneously with surrounding water molecules.

Polarity Dependency of Hydrogen Bonding

The principle that hydrogen bond formation in water strictly requires the polar covalent nature and partial charges of water.

Intermolecular Forces in Water

The collective noncovalent hydrogen-bonding interactions that keep liquid water cohesive under physiological conditions.

Electrostatic Basis of Hydrogen Bonds

The physical attraction governed by Coulomb's law operating between opposite partial electrical charges in polar molecules.

Hydrogen Bond Strength

A bond energy that is substantially weaker than an intramolecular covalent bond but stronger than typical London dispersion forces.

Emergent Properties of Water

The four macro-level physical and chemical behaviors that arise directly from the hydrogen bonding of polar water molecules.

Cohesion of Water

The emergent property whereby water molecules are linked and held together by mutual hydrogen bonds.

Adhesion of Water

The emergent property whereby water molecules form hydrogen bonds with other different polar or charged substances.

Surface Tension of Water

A measure of the force required to stretch or break the surface of liquid water, elevated by collective cohesion.

Moderation of Temperature by Water

The emergent property enabling water to absorb or release large amounts of heat with only minor changes in its own temperature.

Heat Bank Function of Water

The capacity of massive aquatic reserves to absorb solar thermal energy during warm periods and release it during cooler periods.

Expansion Upon Freezing

The emergent property wherein water expands into a lower-density lattice upon transitioning from liquid to solid.

Ice Flotation Property

The consequence of water expanding upon freezing, making solid ice less dense than liquid water.

Versatility of Water as a Solvent

The emergent property allowing water to dissolve a wide array of polar and ionic compounds through dipole interactions.

Solvent of Life

An ecological and biochemical designation for water recognizing it as the universal fluid medium supporting all cellular life.

Capillary Action

The spontaneous upward flow of water through narrow conduits driven by the coordinated actions of cohesion and adhesion.

Four Major Emergent Properties

The collective set containing cohesive behavior, temperature moderation, expansion upon freezing, and solvent versatility.

Specific Heat

The quantity of heat that must be absorbed or lost for $1\,\text{g}$ of a substance to change its temperature by $1^\circ\text{C}$.

High Specific Heat of Water

The unusually high specific heat of water ($1\,\text{cal}/(\text{g}\cdot^\circ\text{C})$) resulting from extensive hydrogen bonding.

Heat Absorption and Hydrogen Bond Cleavage

The thermodynamic event where incoming heat energy is consumed to disrupt hydrogen bonds before accelerating molecular motion.

Heat Release and Hydrogen Bond Formation

The thermodynamic event where falling temperatures allow hydrogen bonds to form, releasing kinetic energy as heat.

Calorie ($\text{cal}$)

The metric heat measurement defined as the energy required to raise the temperature of $1\,\text{g}$ of water by $1^\circ\text{C}$.

Thermal Buffering by Water

The biological stabilization of internal cellular temperatures against external environmental temperature swings.

Kinetic Energy in Water Temperature Change

The vibrational and translational molecular motion that increases only after heat overcomes intermolecular hydrogen bonds.

Climate Stabilization by Oceans

The macro-scale environmental moderation of coastal weather systems by ocean waters absorbing and releasing heat.

Biological Importance of Water Specific Heat

The protection of enzymes and biochemical pathways from thermal denaturation within water-rich living organisms.

Resistance to Temperature Fluctuation

The tendency of water bodies to resist dramatic shifts in temperature when subjected to thermal gains or losses.

Specific Heat Comparison to Nonpolar Liquids

The observation that water possesses a significantly higher specific heat than nonpolar organic solvents like benzene.

Why Ice Floats

Solid water floats because hydrogen bonds stabilize molecules into a spacious crystalline lattice, reducing density below that of liquid water.

Density of Ice

The volumetric mass of solid ice which is approximately $10\%$ less than the volumetric mass of liquid water at $0^\circ\text{C}$.

Crystalline Lattice of Ice

The rigid three-dimensional open framework where each water molecule is hydrogen-bonded to four neighboring water molecules.

Hexagonal Ice Symmetry

The six-sided geometric arrangement assumed by water molecules locked into a frozen crystalline matrix.

Maximum Density of Water at $4^\circ\text{C}$

The specific temperature threshold at which liquid water achieves its highest density before expanding toward freezing.

Molecular Spacing in Ice vs Liquid Water

The condition where water molecules in ice are held farther apart in an ordered lattice than in closely packed liquid water.

Thermal Insulation by Ice Sheets

The protective barrier formed by floating surface ice that shields underlying aquatic ecosystems from sub-freezing air.

Ecological Benefit of Floating Ice

The survival mechanism that prevents aquatic habitats from freezing solid from the bottom up during winter.

Hydrogen Bond Stabilization in Ice

The immobilization of hydrogen bonds into rigid, unbreakable orientations when kinetic energy drops at the freezing point.

Liquid Water Packing

The higher-density state where transient hydrogen bonds continuously break, allowing water molecules to slip closely past one another.

Volume Expansion of Freezing Water

The physical enlargement of water's occupied space upon solidification that exerts mechanical pressure and reduces density.

Aqueous Solution

A homogeneous liquid mixture in which water serves as the solvent that dissolves one or more solutes.

Solution

A completely homogeneous liquid mixture consisting of two or more substances distributed at a molecular level.

Solvent

The dissolving agent of a solution that is typically present in the greatest abundance.

Solute

The substance that is dissolved by a solvent to produce a homogeneous chemical solution.

Hydration Shell

The concentric sphere of oriented water molecules that surrounds and isolates individual dissolved ions or polar molecules.

Dissolution of Ionic Solutes

The separation of ionic lattices by water's negative oxygen poles attracting cations and positive hydrogen poles attracting anions.

Dissolution of Polar Solutes

The solubilization of neutral molecules through the formation of hydrogen bonds between water and polar functional groups.

Water as a Universal Solvent

A traditional description emphasizing water's versatile capacity to dissolve a wider spectrum of chemical substances than any other liquid.

Sphere of Hydration

An alternate term for a hydration shell emphasizing the three-dimensional water shield surrounding a dissolved ion.

Electrostatic Dissolution Mechanism

The physical process wherein charge-charge attractions between water dipoles and solute charges overcome solute-solute cohesive bonds.

Cytoplasmic Aqueous Solution

The internal fluid environment of a biological cell where dissolved proteins, ions, and metabolites undergo biochemical reactions.

Solute Concentration in Water

The quantity of a dissolved chemical entity present within a specified volume of an aqueous solution.

Hydrophilic Substance

Any substance that possesses an electrical affinity for water and readily interacts with or dissolves in it.

Hydrophobic Substance

Any substance that lacks an affinity for water, repelling aqueous interactions and resisting dissolution.

Polar Basis of Hydrophilicity

The chemical property where polar covalent bonds enable molecules to form stabilizing hydrogen bonds with surrounding water.

Nonpolar Basis of Hydrophobicity

The chemical property where nonpolar covalent bonds prevent molecules from establishing favorable electrostatic interactions with water.

Hydrophobic Exclusion

The tendency of water molecules to hydrogen-bond with each other, effectively excluding and clustering nonpolar molecules together.

Hydrophilic Colloid

A suspension of large hydrophilic molecules, like gelatin or cotton, that absorb water without forming a true dissolved solution.

Ionic Compounds as Hydrophiles

Salts whose full ionic charges engage in energetically favorable electrostatic interactions with water dipoles.

Hydrocarbons as Hydrophobes

Molecules rich in nonpolar carbon-hydrogen bonds that separate from aqueous phases, exemplified by oils and fats.

Water Repulsion

The apparent physical pushing away of nonpolar substances driven by the self-association of cohesive water molecules.

Biological Consequence of Hydrophobicity

The structural segregation of nonpolar lipids into membranes and hydrophobic protein cores away from aqueous cytoplasm.

Hydrophilic Solutes

Small polar compounds such as sugars and amino acids that dissolve freely within aqueous biological fluids.

Acid

A substance that increases the hydrogen ion ($H^+$) concentration of an aqueous solution.

Hydrogen Ion ($H^+$)

A single proton stripped of its electron, released when an acid dissociates in an aqueous medium.

Hydronium Ion ($H_3O^+$)

The chemical species formed when a dissociated hydrogen ion associates with a neutral water molecule.

Proton Donor

The classical Bronsted-Lowry functional definition identifying any chemical compound that transfers a proton ($H^+$) to a solution.

Strong Acid

An acid that dissociates completely into hydrogen ions and conjugate anions when dissolved in water.

Weak Acid

An acid that dissociates only partially and reversibly in aqueous solution, establishing a dynamic chemical equilibrium.

Acid Dissociation Reaction

The chemical process whereby an acidic molecule cleaves to liberate a free hydrogen ion into the solvent.

Hydrochloric Acid ($HCl$)

A classic example of a strong inorganic acid that dissociates fully into $H^+$ and $Cl^-$ ions in water.

Elevated $[H^+]$

The chemical hallmark of an acidic solution where the concentration of hydrogen ions surpasses that of hydroxide ions.

Acidic Chemical Shift

The alteration of solution chemistry resulting in lowered pH and protonation of exposed basic chemical groups.

Acidic Solution

An aqueous system exhibiting a pH value below 7 that contains a higher concentration of $H^+$ than $OH^-$.

Base

A substance that reduces the hydrogen ion ($H^+$) concentration of an aqueous solution.

Hydroxide Ion ($OH^-$)

A negatively charged polyatomic ion liberated by basic dissociation or formed by water deprotonation.

Proton Acceptor

The Bronsted-Lowry functional definition characterizing any chemical species that binds and removes free $H^+$ from solution.

Strong Base

A base that dissociates directly and completely in water to yield stoichiometric quantities of hydroxide ions.

Weak Base

A base that accepts protons reversibly, establishing an equilibrium without fully ionizing in water.

Sodium Hydroxide ($NaOH$)

A typical strong inorganic base that ionizes fully in water into sodium cations ($Na^+$) and hydroxide anions ($OH^-$).

Ammonia ($NH_3$) as a Base

A weak base that decreases $[H^+]$ by using an unshared electron pair to bind a proton, forming an ammonium ion ($NH_4^+$).

Reduction of Free $[H^+]$

The primary operational mechanism of a base, achieved either by direct proton binding or by providing $OH^-$ to form water.

Basic Solution

An aqueous system exhibiting a pH value above 7 where the concentration of $OH^-$ exceeds the concentration of $H^+$.

Alkaline Solution

A standard alternative biological term denoting any aqueous solution that behaves as a chemical base.