Chemistry: Molecular Orbitals, Gas Laws, and Thermodynamics Key Concepts

MO Theory

Electrons are delocalized over the whole molecule and explain bond order + magnetism.

Localized Molecular Orbitals

No. They extend across the entire molecule.

σ, σ, π, and π

σ and π = bonding orbitals; σ and π = antibonding (higher energy).

Bond Order Formula

(bonding electrons - antibonding electrons)/2.

Paramagnetic vs Diamagnetic

Paramagnetic = unpaired electrons. Diamagnetic = all paired.

KMT: Temperature and KE

Higher temperature = higher kinetic energy = faster particles.

KMT: Mass and Speed

Lighter gases move faster at the same KE.

5 Postulates of KMT

Tiny particles, constant motion, no IMFs, elastic collisions, KE depends on T.

Boyle's Law

P increases → V decreases (inverse).

Charles' Law

V increases → T increases (direct).

Amonton's Law

P increases → T increases (direct).

Avogadro's Law

V increases → n increases (direct).

Dalton's Law

Total pressure = sum of partial pressures.

Ideal Gas Law

PV = nRT.

STP Conditions

1 atm and 273 K.

Nonideal Gases

High pressure + low temperature.

Three States of Matter

Solid = strong IMFs, liquid = moderate IMFs, gas = weak IMFs + high KE.

Normal Boiling Point

Temperature where vapor pressure = 1 atm.

Triple Point and Critical Point

Triple = all 3 phases coexist. Critical = liquid and gas indistinguishable.

Endothermic Phase Changes

Melting, vaporization, sublimation.

Exothermic Phase Changes

Freezing, condensation, deposition.

Four Types of IMFs

Dispersion, dipole-dipole, hydrogen bonding, ion-dipole.

IMFs and Boiling Point

Stronger IMFs = higher boiling point.

Polarity Rule

Asymmetry + polar bonds = polar molecule.

Solution, Solute, Solvent

Solution = mixture; solute = dissolved; solvent = dissolving medium.

Like Dissolves Like

Polar dissolves polar; nonpolar dissolves nonpolar.

Miscible vs Immiscible

Miscible = mix; immiscible = separate layers.

Beer's Law

A = a b c (absorbance = absorptivity × path length × concentration).

Standard Curve

The concentration of an unknown solution.

Dilution Formula

M1V1 = M2V2.

Molarity

mol of solute / L of solution.

Energy Equations

E = hν; λν = c; E = hc/λ.

Heat Equations

q = m c s ΔT; q = n Cp ΔT; q = n ΔHfus; q = n ΔHvap.

Work and Internal Energy

w = -PΔV; ΔE = q + w.

Density Equation

d = m/V.

R Values

0.08206 L·atm/mol·K or 8.314 J/mol·K.

Key Constants

h = 6.626e-34, c = 3.00e8, NA = 6.022e23, 1 atm = 760 torr.