General Chemistry
General Chemistry tests atomic structure, periodic trends, bonding and geometry, stoichiometry, equilibrium, acid-base behavior, and basic thermodynamics. The exam rewards quick, quantitative reasoning and clear definitions.
Core rules
- Effective nuclear charge rises across a period, so atomic radius falls, ionization energy and electronegativity rise, and metallic character falls.
- VSEPR: electron domains repel to maximize separation. Two domains are linear, three trigonal planar, four tetrahedral, five trigonal bipyramidal, six octahedral.
- Hybridization follows domain count: sp (2), sp2 (3), sp3 (4).
- For limiting-reagent problems, convert each reactant to moles of product and take the smaller value.
- Le Chatelier: adding reactant shifts right; increasing pressure shifts toward fewer gas moles; a catalyst changes rate, not position.
- pH = -log[H+]; for a weak acid, [H+] is approximately the square root of Ka times concentration.
Worked example
Find the pH of 0.01 M HCl and of 0.01 M acetic acid (Ka = 1.8 x 10^-5). HCl is strong, so [H+] = 0.01 M and pH = 2.00. Acetic acid is weak: [H+] = square root(1.8 x 10^-5 x 0.01) = square root(1.8 x 10^-7) = 4.2 x 10^-4 M, so pH = 3.37. The weak acid is far less acidic at the same formal concentration.
Traps
- Do not use pH + pOH = 14 outside about 25 degrees Celsius.
- Strong vs weak is about dissociation, not concentration.
- Convert units before stoichiometry; molarity uses liters, not milliliters.