# Chemistry study guides

Canonical: https://duckyhelper.com/learn/chemistry/
Updated: 2026-10-01

Plain-language chemistry guides for high school and AP students. Each one explains the idea, works through real problems with every unit shown, lists the mistakes teachers see most, and ends with practice questions you can check. Every numeric answer on these pages was recomputed in code from IUPAC atomic weights.

- [How to balance chemical equations](https://duckyhelper.com/learn/chemistry/balancing-chemical-equations/): Balance chemical equations step by step: count atoms, change only coefficients, handle fractions and polyatomic ions. 4 worked examples and 5 practice problems.
- [Types of chemical reactions](https://duckyhelper.com/learn/chemistry/types-of-chemical-reactions/): The 5 types of chemical reactions: synthesis, decomposition, single and double replacement, combustion. How to spot each, predict products, and practice.
- [The mole and molar mass](https://duckyhelper.com/learn/chemistry/mole-and-molar-mass/): What a mole is, how to find molar mass, and how to convert grams, moles and particles. Worked examples with units, common mistakes and 5 practice problems.
- [Stoichiometry: how much reacts and how much forms](https://duckyhelper.com/learn/chemistry/stoichiometry/): Learn stoichiometry in three steps: grams to moles, mole ratio, moles to grams. Worked examples with every unit shown, common mistakes and 5 practice problems.
- [How to find the limiting reactant](https://duckyhelper.com/learn/chemistry/limiting-reactant/): Find the limiting reactant and excess reactant step by step, then the product amount and leftover. Worked examples in moles and grams plus 5 practice problems.
- [How to calculate percent yield](https://duckyhelper.com/learn/chemistry/percent-yield/): How to calculate percent yield: find the theoretical yield with stoichiometry, then divide actual by theoretical. Worked examples and 5 practice problems.
- [Molarity and dilution](https://duckyhelper.com/learn/chemistry/molarity-and-dilution/): Molarity is moles of solute per liter of solution. Learn the molarity formula, M1V1 = M2V2 for dilutions, worked examples with units and 5 practice problems.
- [The ideal gas law: PV = nRT](https://duckyhelper.com/learn/chemistry/ideal-gas-law/): Use the ideal gas law PV = nRT and the combined gas law. Which R to use, converting to kelvins, worked examples with units and 5 practice problems with answers.
- [How to write electron configurations](https://duckyhelper.com/learn/chemistry/electron-configuration/): Write electron configurations step by step: filling order, noble gas shorthand, ions, Hund's rule and the Cr and Cu exceptions, plus 5 practice questions.
- [Periodic trends](https://duckyhelper.com/learn/chemistry/periodic-trends/): Periodic trends made simple: atomic radius, ionization energy, electronegativity and ion size, the reason for each, real data and 5 practice questions.
- [Ionic vs covalent bonds](https://duckyhelper.com/learn/chemistry/ionic-vs-covalent-bonds/): Ionic vs covalent bonds: electron transfer vs sharing, the electronegativity difference rule, a properties table, ionic formulas and 5 practice questions.
- [How to draw Lewis structures](https://duckyhelper.com/learn/chemistry/lewis-structures/): Draw Lewis structures in 6 steps: count valence electrons, connect atoms, fill octets, add multiple bonds, check formal charge. Plus 5 practice questions.
- [VSEPR theory and molecular shapes](https://duckyhelper.com/learn/chemistry/vsepr-molecular-shapes/): Predict molecular shape with VSEPR: count electron groups and lone pairs, read the shapes chart, find bond angles and polarity, then try 5 practice questions.
- [Acids, bases and pH](https://duckyhelper.com/learn/chemistry/acids-bases-and-ph/): Acids, bases and the pH scale: pH = -log[H3O+], pOH, strong vs weak acids, conjugate pairs and pH significant figures, with examples and 5 practice problems.

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