General Chemistry I: Bonding and Periodic Trends

Periodic trends

Atomic radiusdecreases → across, increases ↓ down
Ionization energyincreases →, decreases ↓
Electronegativityincreases →, decreases ↓
Metallic characterdecreases →, increases ↓

All four follow from effective nuclear charge rising across a period while shielding stays flat, and a new shell being added down a group.

Bond types

VSEPR geometry

2 regionslinear, 180°
3 regionstrigonal planar, 120°
3, one lone pairbent, <120°
4 regionstetrahedral, 109.5°
4, one lone pairtrigonal pyramidal, ~107°
4, two lone pairsbent, ~104.5°
5 regionstrigonal bipyramidal, 90/120°
6 regionsoctahedral, 90°

Count regions, not atoms. Lone pairs occupy a region and push harder than bonding pairs, which is why the angles compress.

Molecular polarity

Polar bonds plus asymmetric geometry gives a polar molecule. CO2 has two polar bonds and is nonpolar because they cancel; H2O has the same two polar bonds bent, so they do not.

Intermolecular forces, weakest to strongest

  1. London dispersion, in everything, grows with molar mass
  2. Dipole-dipole, polar molecules
  3. Hydrogen bonding, H bonded to N, O or F
  4. Ion-dipole, in solutions of salts

Stronger IMFs mean higher boiling point, higher viscosity, lower vapour pressure.

Stoichiometry

Limiting reagent: convert each reactant to moles of product and take the smaller. Percent yield = actual/theoretical × 100.

Gas laws

T is always in kelvin. K = °C + 273.15.

Thermochemistry