← Bonding, structure, properties and energy changes

Polarity, IMFs → properties (every paper)

Symmetric → dipoles cancel → non-polar. IMF strength decides the property.

Property argument, in order

• Name the IMF(s) in each substance.
• Compare strength (London: bigger molar mass/electron cloud = stronger).
• Link: stronger IMF → more energy to separate → higher mp/bp; or H-bonds with water → soluble.

Exam classic CH₃CH₂OH (78 °C) vs CH₃OCH₃ (−24 °C) Same formula C₂H₆O — why such different boiling points? Ethanol has O–H → intermolecular hydrogen bonding. Dimethyl ether: no H on O → polar only → dipole-dipole. H-bonds > dipole-dipole → more energy to separate ethanol → higher bp. ✓ H-bonding vs dipole-dipole; stronger IMFs → higher bp.

Deciding polarity from symmetry, step by step

• Draw the Lewis structure and identify every polar bond (a bond between atoms of different electronegativity).
• If there are NO polar bonds at all, the molecule is non-polar regardless of shape.
• If there ARE polar bonds, check the SHAPE: do the bond dipoles point in directions that cancel (symmetric arrangement) or not (asymmetric)?
• Cancel → non-polar overall (e.g. CO₂, linear). Do not cancel → polar overall (e.g. H₂O, bent).

Practice for this standard covers the whole topic — flashcards and quiz.