Why study these two sections first
According to the official CSCA Chemistry Examination Syllabus (2025 Edition), the exam lasts 60 minutes and contains 48 multiple-choice questions, with a full score of 100. Time is short and the question count is high, so when reviewing you should prioritize the sections that appear repeatedly and can be scored quickly.
The syllabus content directly related to these two sections includes:
- The “Chemical Theories and Laws” module: atomic structure and the periodic law of elements, chemical bonds and intermolecular forces, and electrolyte solution theory
- The “Properties and Reactions of Substances” module: ionic reactions and testing methods
- The “Basic Chemical Concepts and Calculations” module: solution concentration and pH calculations
This shows that atomic structure, periodic trends and chemical bonds, together with ionic reactions and electrolyte solutions, are not scattered minor points but content explicitly listed for assessment in the syllabus.
We counted 4 past papers (2025-12-21, 2026-01-25, 2026-03-15, 2026-04-25), with a total of 185 questions (all compiled from candidate recollections, with 7 questions missing), and classified them into 9 sections. The results are as follows:
- Atomic structure, periodic trends and chemical bonds: 28 questions; the four papers had 6, 8, 6 and 8 questions respectively
- Ionic reactions and electrolyte solutions: 28 questions; the four papers had 8, 7, 8 and 5 questions respectively
- The two sections total 56 questions, about 30%
In other words, these two sections are tested in every paper, and each accounts for 5 to 8 questions per paper. If you learn them solidly first, you secure nearly 30% of the questions on the paper.
Atomic structure, periodic trends and chemical bonds: what you need to know
The key to this section is clear concepts and accurately memorized rules. First, memorize the quantitative relationships inside an atom:
- In an atom: number of protons = nuclear charge = number of extranuclear electrons
- Mass number A = number of protons Z + number of neutrons N
For example: a sodium atom has 11 protons and a mass number of 23, so the number of neutrons is 23 − 11 = 12.
You should also be able to recognize the definition of isotopes at a glance: same number of protons but different numbers of neutrons.
You need to be able to use the periodic law:
- Across a period from left to right, metallic character weakens and non-metallic character strengthens
- Down a main group from top to bottom, metallic character strengthens and non-metallic character weakens
For chemical bonds, start by distinguishing the two basic cases:
- Ionic bonds generally form between active metals and active non-metals
- Covalent bonds generally form between non-metal atoms
One more point: intermolecular forces affect physical properties such as melting point and boiling point. When answering “Why does this substance have a higher boiling point?”, first determine whether the substance is an ionic compound or a molecule, then look at the intermolecular forces — and your reasoning will not become muddled.
Ionic reactions and electrolyte solutions: what you need to know
The core of this section is writing ionic equations correctly. There is only one rule, but you must memorize it and apply it fluently:
- Strong acids, strong bases and soluble salts are split into ions
- Weak electrolytes, precipitates, gases and water are written as chemical formulas
After writing an equation, always check two things:
- Conservation of atoms
- Conservation of charge
Be able to write these two standard examples from memory:
- Hydrochloric acid and sodium hydroxide: H⁺ + OH⁻ = H₂O
- Silver nitrate and sodium chloride: Ag⁺ + Cl⁻ = AgCl↓
Ion coexistence questions follow the same logic: ions that can form a precipitate, a gas or water cannot coexist in large amounts. When you see such a question, first ask yourself, "Will these two ions form a precipitate, a gas or water when they meet?" The answer usually follows.
For pH, remember the formula: pH = −lg c(H⁺); at room temperature (25 °C), a neutral solution has pH = 7. Because calculators are not allowed in the exam, practice pH calculations until you can do them by hand fluently.
Review advice
- First memorize the positions of the first 20 elements in the periodic table. Once you know them well, periodic trend questions become much faster, and you will not have to work them out from scratch each time.
- Write a few ionic equations every day, and after writing them check them against conservation of atoms and conservation of charge. It does not matter if you are slow; getting them right matters most.
- Calculators are prohibited in the chemistry exam, so you must be able to calculate pH by hand. Do not use a calculator in daily practice, so that you do not feel uncomfortable in the exam room.
Next steps
First take the chemistry 15-minute diagnostic to see roughly where you stand on these two sections; then go to knowledge point learning to fill gaps section by section and put the rules above into practice one by one.