Chemistry: Atomic Structure, Bonding and Reactions
What the paper tests
Topics include atomic structure and the periodic table, chemical formulas and equations, bonding, acids and bases, oxidation and reduction, and basic organic chemistry. Expect balancing equations, identifying reaction types, and simple mole or concentration calculations.
Concepts to master
An atom has protons and neutrons in the nucleus with electrons in shells; atomic number is protons, mass number is protons plus neutrons, and isotopes differ in neutrons. The periodic table groups elements by valence electrons, which explains similar chemical behaviour down a group. Ionic bonds transfer electrons between metals and non-metals; covalent bonds share electrons between non-metals. Acids release hydrogen ions in water, bases neutralise them to give salt and water. Oxidation is loss of electrons, reduction is gain; the two always occur together. Know the common formulas: water, carbon dioxide, sulphuric acid, sodium hydroxide, calcium carbonate.
Traps
Unbalanced equations that look correct; confusing atomic number with mass number; thinking all covalent compounds conduct electricity; and forgetting that gases must be shown as diatomic molecules when balancing.
Rule of thumb
Balance equations by counting each element on both sides and adjusting coefficients only, never subscripts. Check hydrogen and oxygen last.
Worked example
Balance hydrogen burning in oxygen. Write H2 + O2 gives H2O. Two oxygen atoms on the left need two water molecules on the right: H2 + O2 gives 2H2O. That gives four hydrogen on the right, so use 2H2 + O2 gives 2H2O.