The topics in Chemistry can be divided up in many ways so it is sometimes difficult to index them in a sensible way.

Changing materials includes:
Salt preparation
Useful products from oil
Useful products from air
Useful products from rocks
Representing reactions
Quantitative chemistry
Earth and Atmosphere
The rock record

Classifying materials includes:
Acids and bases
Atomic structure
Bonding
Chemical analysis
Metals and non-metals
Noble gases
Physical changes
Titrations and titration calculations

Patterns of behaviour includes:
Reactivity series
The Periodic Table
Changes in reactivity down a group
Chemical reactions
Group I metals
Transition metals
Combustion
Group VII - the halogens
Oxidation
Electrolysis of brine
Acids and alkalis
Rates of reactions
Reactions involving enzymes
Reversible reactions
Energy transfer in reactions

To help, here are the current Revisionworld topics of GCSE Chemistry, arranged in alphabetical order with some help to tell you where to look.

Acids and alkalis                                        P        Patterns of behaviour
Acids and bases                                         CL      Acids and bases
Aluminium                                                   CH      Useful products from rocks
Ammonia                                                     CH      Useful products from air
Balancing equations                                 CH      Representing reactions
Bonding introduction                                CL      Atomic structure
Calculating masses                                   CH      Quantitative chemistry
Changes in reactivity down a group     P         Patterns of behaviour
Changes of physical state                       CL      Physical changes
Chemical reactions                                    P        Patterns of behaviour
Choosing an indicator                               CL      Acids and bases
Combustion                                                 P        Patterns of behaviour
Copper                                                          CH      Useful products from rocks
Corrosion                                                     CH      Useful products from rocks
Covalent bonding                                       CL      Atomic structure
Cracking and its products                        CH      Useful products from oil
Earth and Atmosphere                            CH      Earth and Atmosphere
Electrolysis of brine                                  P        Patterns of behaviour
Energy shells                                              CL      Atomic structure
Energy transfer in reactions                  P        Patterns of behaviour
Fertiliser from ammonia                         CH      Useful products from air
Fractional distillation                               CH      Useful products from oil
Fuels                                                             CH      Useful products from oil
Group I metals                                           P        Patterns of behaviour
Group VII - the halogens                        P        Patterns of behaviour
History of the atom                                  CL      Atomic structure
How scientists represent atoms           CL      Atomic structure
Insoluble salts                                           CH      Salt preparation
Instrumental methods of analysis       CL      Chemical analysis
Ionic bonding                                             CL      Atomic structure
Iron and the Blast Furnace                    CH      Useful products from rocks
Limestone                                                   CH      Useful products from rocks
Metallic bonding                                         CL      Atomic structure
Metals and non-metals                            CL      Metals and non-metals
Mortar, cement, concrete and glass   CH    Useful products from rocks
Noble gases                                                CL       Noble gases
Ores and reactivity                                  CH      Useful products from rocks
Oxidation                                                    P         Patterns of behaviour
Particles                                                     CL       Physical changes
Plastics                                                       CH      Useful products from oil
Problems from overuse of fertiliser   CH      Useful products from air
Rates of reactions                                    P        Patterns of behaviour
Reacting masses                                      CH      Quantitative chemistry
Reactions involving enzymes                P        Patterns of behaviour
Reactivity series                                       P        Reactivity series
Reversible reactions                                P         Patterns of behaviour
Solids, liquids and gases                         CL      Physical changes
Soluble salts A                                          CH      Salt preparation
Soluble salts B                                          CH      Salt preparation
Structures                                                  CL      Atomic structure
Test tube reactions for negative ions CL      Chemical analysis
Test tube reactions for positive ions   CL      Chemical analysis
The mole                                                     CH      Quantitative chemistry
The Periodic Table                                    P        The Periodic Table
The rock record                                        CH      The rock record
Titrations                                                   CH      Quantitative chemistry
Titrations (thinking method)                CH      Quantitative chemistry
Transition metals                                     P        Patterns of behaviour
What is crude oil?                                    CH      Useful products from oil
What's in an atom?                                 CL       Atomic structure
Which method to use                             CH      Salt preparation