IMF flashcards

Intramolecular

Forces within a molecule (chemical bonds: ionic, covalent, metallic)

Intermolecular

Forces between molecules

Bond Polarity

Caused by differences in electronegativity (EN).

Nonpolar bond

Atoms have equal EN (e.g., O₂).

Polar bond

One atom is more EN → creates partial charges (δ⁺ and δ⁻).

Molecular Polarity

Depends on shape and symmetry.

Symmetrical

Nonpolar (e.g., CO₂, CCl₄)

Asymmetrical

Polar (e.g., H₂O, PH₃)

BEND Rule (Bond Electronegativity Difference)

ΔEN = 0 → nonpolar; ΔEN > 0 → polar

Example polarity ranking

O₂ < CO₂ < HCl < HF

London Dispersion (LDF)

All molecules (especially nonpolar); Weakest (~0.1-5 kJ/mol); Temporary dipoles; increases with size/polarizability

Dipole-Dipole

Polar molecules; Medium (~5-20 kJ/mol); δ⁺ of one attracted to δ⁻ of another

Hydrogen Bonding

H bonded to N, O, or F; Strongest (~5-50 kJ/mol); Special dipole-dipole; high boiling/melting points

Boiling Point & Melting Point

↑ IMF → ↑ boiling/melting point

Viscosity

↑ IMF → ↑ resistance to flow

Vapor Pressure

↑ IMF → ↓ vapor pressure

Boiling Points of Noble Gases (LDF Trend)

Ne < Ar < Kr < Xe

Alkanes (LDF & Size)

CH₄ (gas) < Butane (gas/liquid) < Hexane (liquid) < Icosane (solid); Longer chains = more surface area = stronger LDFs

Hydrogen Bonding in Group VIA Hydrides

H₂O > H₂S > H₂Se > H₂Te (boiling point trend); H₂O has strongest H-bonding due to high EN and small size of O

Diatomic molecule

A molecule made of two atoms (e.g., O₂, N₂).

7 Diatomic Elements

H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂

Ionic vs. Covalent Boiling Point

Ionic compounds generally have higher boiling points due to stronger electrostatic forces.

Cation

Positively charged ion (lost electrons)

Anion

Negatively charged ion (gained electrons)

Roman Numerals

Indicate the oxidation state of transition metals in ionic compounds.