Global challenges Study Guide

Organic compounds are molecules primarily composed of carbon and hydrogen atoms, often with other elements like oxygen, nitrogen, and halogens. The vast diversity of organic compounds arises from carbon's ability to form stable bonds with itself and with other atoms in various arrangements. However, despite the complexity of entire molecules, their chemical behaviour is largely determined by specific groups of atoms called functional groups. A functional group is a specific arrangement of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule. For example, all molecules containing a hydroxyl (-OH) group, like ethanol (CH₃CH₂OH), will exhibit similar reactions due to the presence of this functional group, such as reacting with sodium or undergoing oxidation. Similarly, compounds with a carboxyl (-COOH) group, like ethanoic acid (CH₃COOH), will behave as acids. The rest of the molecule, often referred to as the 'alkyl group' or 'R group', primarily influences physical properties like boiling point and solubility, but has a less direct impact on the fundamental chemical reactions. This concept simplifies the study of organic chemistry significantly, as understanding the reactions of a few common functional groups allows prediction of the behaviour of a huge number of different organic compounds. It enables chemists to classify organic compounds into homologous series, where members share the same functional group and thus similar chemical properties, exhibiting a gradual change in physical properties as the carbon chain length increases.

The greenhouse effect is a natural process that warms the Earth's surface. When the Sun's energy reaches Earth, some of it is reflected back into space, but most of it is absorbed by the land and oceans, warming the planet. This warmed surface then radiates energy back towards space in the form of longer-wavelength infrared radiation. Certain gases in the Earth's atmosphere, known as greenhouse gases, absorb this outgoing infrared radiation. Instead of allowing all of this energy to escape directly into space, these gases re-emit the infrared radiation in all directions, including back towards the Earth's surface. This re-emission of energy traps heat within the atmosphere, preventing the planet from becoming too cold to support life. Without the natural greenhouse effect, the Earth's average temperature would be around -18°C, rather than the current average of approximately +15°C. The key greenhouse gases include water vapour, carbon dioxide, methane, and nitrous oxides.