Key Terms
Example
N-pentane (bp 36 C) > isopentane (bp 27 C) > neopentane (bp 9.5 C); same formula, different shape
To predict boiling point or vapor pressure
1. Identify all IMF types present in each molecule 2.
Definition
Temperature at which vapor pressure equals surrounding atmospheric pressure Normal boiling point: when surrounding press
Formula
H = (2T cos theta) / (r * rho * g)
Two-point form
Ln(P1/P2) = (delta-H vap / R) * (1/T2 - 1/T1)
Use this equation to
1. Find delta-H vap given two (T, P) pairs 2.
Triple point
Specific (T, P) where solid, liquid, and vapor coexist in equilibrium
Critical point
Temperature and pressure above which distinct liquid phase cannot exist
Liquid-vapor curve
Shows boiling point at any pressure; extends from triple point to critical point Solid-liquid curve: shows melting point
Crystalline
Particles arranged in a definite, repeating 3D pattern
Amorphous (noncrystalline)
Particles in random arrangement; no long- range order
Unit cell
Smallest repeating unit of a crystal; repeat in 3 dimensions to build the entire structure Lattice points: represent ato
Simple cubic
Edge length = 2r (atoms touch along edge) BCC: body diagonal = 4r; edge length = (4r) / sqrt(3) FCC: face diagonal = 4r;
Bragg Equation
N * lambda = 2d * sin(theta)
All molecules
London dispersion forces (always present, even in noble gases and nonpolar molecules)