S3.1The periodic table: classification of elements
Key terms
Period
A horizontal row: elements with the same number of occupied electron shells.
Group
A vertical column: elements with the same number of valence electrons and similar chemistry.
Electronegativity
Ability of an atom to attract a bonding pair of electrons.
Electron affinity
Energy change when one mole of electrons is added to one mole of gaseous atoms.
Oxidation state
A charge assigned to an atom assuming all its bonds are ionic.
Blocks: s (groups 1–2), p (13–18), d (transition elements), f (lanthanoids and actinoids). Metals are on the left, non-metals on the right, metalloids (B, Si, Ge, As, Sb, Te) between.
The full notes, worked example, interactive diagram and check questions for this subtopic are in the app.
Exam tip: Trend explanations need three ideas: nuclear charge, shielding (number of inner shells) and distance from the nucleus.
S3.2Functional groups: classification of organic compounds
Key terms
Homologous series
Compounds with the same functional group and general formula, differing by CH₂, with gradually changing physical properties.
Functional group
The atom or group of atoms that gives a compound its characteristic reactions.
Structural isomers
Compounds with the same molecular formula but a different arrangement of atoms.
Saturated / unsaturated
Contains only single C–C bonds / contains at least one C=C or C≡C bond.
Formulas: molecular (C₂H₆O), empirical, full structural (all bonds), condensed (CH₃CH₂OH) and skeletal (lines, with C and H on carbon not shown).
The full notes, worked example, interactive diagram and check questions for this subtopic are in the app.
Exam tip: Always find the longest continuous carbon chain first: it may bend around corners in a drawn structure.