Comprehensive Midterm Chemistry: Molecular Structure, Gas Laws, and States of Matter

VSEPR Theory

The fundamental concept explaining molecular geometry.

Molecular Geometry

The spatial arrangement of atoms (e.g., Tetrahedral).

Electron-Domain Geometry

The spatial arrangement of electron groups (bonding/lone pairs).

Hybridization

The mixing of atomic orbitals ($s$, $p$, $d$) to form new orbitals.

sp, sp², sp³

Specific types of hybrid orbitals and their associated geometries.

Lone Pair

Non-bonding valence electrons on the central atom.

Bonding Pair

Electrons shared between two atoms.

Electronegativity

The ability of an atom to attract electrons in a bond.

Dipole Moment

A measure of net molecular polarity.

Polar Molecule

A molecule with a net dipole moment (asymmetrical).

Nonpolar Molecule

A molecule where dipole moments cancel (symmetrical).

Sigma ($\sigma$) Bond

Bond formed by head-to-head overlap (single bonds).

Pi ($\pi$) Bond

Bond formed by side-by-side overlap (in double/triple bonds).

Resonance Structure

Two or more equivalent Lewis structures for a single molecule.

Ideal Bond Angle

The theoretical angle for a specific geometry (e.g., $109.5^\circ$ for tetrahedral).

Trigonal Planar

Geometry with three electron domains (e.g., $\text{BF}_3$).

Trigonal Pyramidal

Geometry with one lone pair and three bonding pairs (e.g., $\text{NH}_3$).

Intermolecular Forces (IMFs)

Forces between molecules affecting physical properties.

London Dispersion Forces (LDF)

Weakest IMF; present in all substances; increases with molar mass.

Dipole-Dipole Forces

Forces between permanent dipoles of polar molecules.

Hydrogen Bonding

Strongest IMF; H bonded to N, O, or F.

Vapor Pressure

The pressure exerted by a vapor in equilibrium with its liquid or solid phase.

Boiling Point

The temperature at which vapor pressure equals external pressure.

Phase Change

The transition of matter from one state to another.

Sublimation

Solid directly to gas (Endothermic).

Deposition

Gas directly to solid (Exothermic).

Vaporization/Evaporation

Liquid to gas (Endothermic).

Condensation

Gas to liquid (Exothermic).

Melting/Fusion

Solid to liquid (Endothermic).

Freezing

Liquid to solid (Exothermic).

Viscosity

A liquid's resistance to flow.

Surface Tension

The energy required to increase the surface area of a liquid.

Crystalline Solid

A solid with a highly ordered, repeating structure (lattice).

Amorphous Solid

A solid lacking a well-defined crystal structure (e.g., glass).

Pressure (P)

Force exerted per unit area. Units: atm, $ ext{mmHg}$, Torr, $ ext{kPa}$.

Volume (V)

The amount of space occupied by the gas. Units: L, $ ext{mL}$.

Temperature (T)

A measure of the average kinetic energy of gas particles. *MUST be in Kelvin (K).*

Moles (n)

The amount of gas particles.

Boyle's Law

Inverse relationship between P and V (at constant T, n).

Charles's Law

Direct relationship between V and T (at constant P, n).

Ideal Gas Law

The equation relating all four variables: $PV=nRT$.

Ideal Gas Constant (R)

The numerical constant used in the Ideal Gas Law ($0.0821 rac{ ext{L} ext{atm}}{ ext{mol} ext{K}}$).

Absolute Zero

The theoretical temperature at which gas volume is zero ($0 ext{ K}$ or $-273.15^ ext{C}$).

Standard Temperature and Pressure (STP)

Defined conditions: $0^ ext{C}$ ($273.15 ext{ K}$) and $1 ext{ atm}$.

Dalton's Law of Partial Pressures

The total pressure of a gas mixture is the sum of the partial pressures.

Partial Pressure

The pressure exerted by an individual gas in a mixture.

Mole Fraction ($ ext{χ}$)

The ratio of the moles of a gas to the total moles in the mixture.

Kinetic Molecular Theory (KMT)

A model explaining gas behavior based on molecular motion.

Diffusion

The mixing of gases due to random molecular motion.

Effusion

The escape of gas through a tiny hole into a vacuum.

Real Gas

Gases that deviate from ideal behavior, especially at high pressure or low temperature.