Assessment and Qualifications Alliance (AQA) GCSE Chemistry Paper 1 Practice Exam

The main difference between a compound and a mixture lies in the nature of chemical bonding. Compounds are made up of two or more different elements that are chemically bonded together in a fixed ratio. This bonding results in the formation of molecules or ionic structures, which exhibit properties distinct from the individual elements that make them up. For example, water (H₂O) is a compound composed of hydrogen and oxygen atoms bonded together, resulting in a substance with specific chemical and physical properties.

In contrast, a mixture consists of two or more substances that are combined physically rather than chemically. The components of a mixture retain their individual properties and can be separated by physical means, such as filtration or evaporation. For example, sand and salt can be mixed together, but they do not form a new substance; rather, they maintain their separate identities and can be easily separated.

This understanding highlights why the correct answer asserts that while compounds are formed through the chemical bonding of elements, mixtures are not bound by such chemical connections and therefore retain the characteristics of their individual components.