Course Introduction This course covers C5.1, 5.2 and 5.3 from Module C5: Chemicals of the Natural Environment which is examined on Paper 1 of the GCSE OCR Chemistry A Course.  It also covers part of C4.3 from Module C4: Chemical Patterns. This course aims to answer a number of questions: C5.1 What types of chemicals make up the atmosphere? C5.2 What reactions happen in the hydrosphere? C5.3 What types of chemicals make up the Earth’s lithosphere? C4.3 How do chemists explain the properties of compounds of Group 1 and Group 7 elements? This Module is completed by Chemicals of the Natural Environment 2: OCR A Chem

Compounds and Elements in the Earth Dry air consists of gases, some of which are elements (for example, oxygen, nitrogen and argon) and some of which are compounds (for example, carbon dioxide). The relative proportions of the main gases in the atmosphere are about 78% nitrogen, 21% oxygen, 1% argon and 0.04% carbon dioxide. The Earth’s hydrosphere (oceans, seas, lakes and rivers) consists mainly of water with some dissolved compounds, called salts. The Earth’s lithosphere (the rigid outer layer of the Earth made up of the crust and the part of the mantle just below it) is made up of a mixture of minerals. Silicon, oxygen and aluminium are very abundant elements in the Earth’s crust. Much of the silicon and oxygen is present in the Earth’s crust as the compound silicon dioxide

Try to familiarise yourself with these tables.  In the exam, you may be asked to interpret the results of adding aqueous sodium hydroxide to solutions of salts or interpret the results of the tests for negative ions, given these tables.