the one idea that runs the course
Almost every gen chem problem is a unit conversion with the mole in the middle.
You can't count atoms, so chemistry counts them in bundles. Get to moles first, then go anywhere. If a problem feels impossible, find which box you're starting in and which box you need to end in. The path between them is the answer.
Particles
atoms · molecules · ions
× 6.022×10²³ from moles
× 6.022×10²³ from moles
Grams
÷ molar mass to moles
× molar mass back
× molar mass back
Moles
the hub
Liters of solution
× molarity to moles
÷ molarity back
÷ molarity back
Moles of B
× mole ratio
from the balanced equation
from the balanced equation
Plant version: moles are cases on a pallet. Nobody counts individual cups on a receiving dock. You count cases, and the case count converts to cups, pounds, or pallets. Molar mass is just "how much does one case weigh."
Open the interactive Mole Map →
Ch 1 — Matter, Energy & Measurement
Covered
CHM 151
Sig Fig Checker
See which digits count, and round calculations with the × ÷ and + − rules.
CHM 151
Dimensional Analysis
Build conversion chains by tapping factors until the units cancel. Gallons, ppm, flow rates.
CHM 151
Matter & Density
Classification and physical vs. chemical sorting games, a density column, and a d = m/V solver.
Ch 2 — Atoms, Molecules & Ions
Covered
CHM 151
Atomic Structure
Build an atom, then see isotopes, ions, and how average atomic mass is weighted.
CHM 151
Ions & Naming Compounds
Ionic, molecular, and acid naming rules, plus a compound builder with labels you've seen at work.
Ch 3 — Chemical Reactions & Stoichiometry
Covered
CHM 151
Balancing Equations
Balance with +/− coefficients and a live atom tally, plus hints, an auto-balancer for any equation, and reaction-type sorting.
CHM 151
The Mole Map
Pick a start and an end. It walks grams → moles → mole ratio → grams with units canceling.
CHM 151
Limiting Reactant: The Batch Sheet
Batches each reactant supports, theoretical yield, leftover excess, and % yield.
CHM 151
Empirical & Molecular Formulas
Percent → moles → ratio → formula, step by step. Why glucose and lactic acid share CH₂O.
Ch 4 — Reactions in Aqueous Solution
CHM 151
Reactions in Water
Electrolytes, solubility rules, and a solution mixer that writes molecular, complete ionic, and net ionic equations.
CHM 151
Oxidation–Reduction
Oxidation number calculator, who's oxidized and reduced, and the activity series.
CHM 151
Molarity & Titration
Molarity, dilution, a titration curve you drag through, and the chemistry under the TA test.
Ch 5 — Thermochemistry
CHM 151
Heat, q = mcΔT & Calorimetry
Specific heat, calorimetry, and the HTST regen section as an energy balance.
CHM 151
Hess's Law & ΔHf°
A flip-and-scale Hess puzzle, a ΔHf° calculator, and the 4-4-9 behind nutrition labels.
Ch 6 — Electronic Structure of Atoms
CHM 151
Light & the Quantum Atom
EM spectrum slider, hydrogen line spectrum, photoelectric effect, de Broglie, quantum numbers.
CHM 151
Electron Configuration
Clickable periodic table with orbital box diagrams, Hund's rule, and the Cr/Cu exceptions.
Ch 7 — Periodic Properties of the Elements
Ch 8 — Basic Concepts of Chemical Bonding
Ch 9 — Molecular Geometry & Bonding Theories
CHM 151
Bonding & Molecular Shapes
Electronegativity tug-of-war, VSEPR, and 3D molecules you can rotate.
CHM 151
Hybridization & MO Theory
sp/sp²/sp³, σ vs π counts, and MO diagrams with bond order and magnetism.
Ch 10 — Gases
Look-ahead
Chapters follow Brown, LeMay et al., Chemistry: The Central Science.
For Your Eyes Only
Quick Reference
Avogadro's number
1 mol = 6.022 × 10²³
particles per mole — one "case"
Molar mass
g/mol from the table
add the atomic masses in the formula
Molarity
M = mol solute ÷ L solution
liters of solution, not solvent
Dilution
M₁V₁ = M₂V₂
moles of solute don't change when you add water
Percent yield
actual ÷ theoretical × 100
theoretical comes from the limiting reactant
Density
d = m ÷ V
a conversion factor between mass and volume
Sig figs · × ÷
fewest sig figs wins
count sig figs in each measured value
Sig figs · + −
fewest decimal places wins
line up the decimals, cut at the shortest