Chemistry Content: Organic Chemistry, Biochemistry, and Nuclear Chemistry
This domain covers organic functional groups and reactions, major biomolecules, and nuclear changes. Expect nomenclature and isomer questions, recognition of reaction types, and half-life or decay calculations.
Core rules and concepts
- Functional groups determine properties: alcohols (−OH), aldehydes and ketones (carbonyl), carboxylic acids, esters, amines, and amides.
- Isomers have the same molecular formula but different structures. Structural isomers differ in connectivity; stereoisomers differ in spatial arrangement.
- Addition reactions occur at double or triple bonds; substitution replaces an atom or group; elimination forms a multiple bond.
- Biomolecules include carbohydrates, lipids, proteins, and nucleic acids. Proteins are polymers of amino acids linked by peptide bonds.
- Nuclear decay: alpha emission decreases mass number by 4 and atomic number by 2; beta-minus emission keeps mass number and increases atomic number by 1; gamma emission changes neither.
- Half-life is the time for half a sample to decay. After n half-lives, remaining amount = initial × (1/2)^n.
Worked example
A sample has 64 g of a radioisotope with a half-life of 8 days. After 24 days, n = 24 ÷ 8 = 3 half-lives. Remaining mass = 64 g × (1/2)^3 = 64 × 1/8 = 8 g. The amount decays exponentially, not linearly.
Traps that cost marks
Do not confuse aldehydes and ketones; an aldehyde has the carbonyl at a chain end. Do not treat beta decay as changing mass number. Do not assume half-life means all sample is gone after two half-lives. In organic naming, identify the longest chain and the principal functional group before numbering.