Elements, compounds and mixtures Study Guide

When working with mixtures in biology or chemistry, it's often necessary to separate components to purify a substance or analyse its constituents. The choice of purification technique depends critically on the physical and chemical properties of the substances involved. Key properties to consider include differences in boiling points, solubility, particle size, and magnetic properties. For example, if you have a mixture of a dissolved solid in a liquid, evaporation or distillation might be suitable. Evaporation removes the liquid, leaving the solid behind, while distillation separates the liquid from the solid and collects both. If a solid is insoluble in a liquid, filtration is an effective method. If you have two immiscible liquids with different densities, decantation or using a separating funnel would be appropriate. Crystallisation is used to obtain pure solid samples from a solution by carefully controlling the evaporation of the solvent. Sometimes, more complex techniques like chromatography are needed to separate components within a mixture, especially if they have similar properties or are present in small quantities, but these are typically considered for more advanced applications. Understanding the characteristics of the components in a mixture is the first step in selecting an appropriate and efficient purification strategy.

Chemical bonding is the process of chemical substances combining to form molecules and compounds, driven by atoms seeking a stable electron configuration, typically a full outer shell. The type of bonding significantly influences a substance's physical and chemical properties. Ionic compounds form between metals and non-metals through the transfer of electrons, creating oppositely charged ions held together by strong electrostatic forces in a giant ionic lattice. Simple molecules, like water or carbon dioxide, form when non-metals share electrons to achieve stable outer shells, resulting in covalent bonds. These molecules are discrete units with weak intermolecular forces between them. Giant covalent structures, such as diamond or silicon dioxide, are formed from non-metal atoms covalently bonded together in a continuous, extended network, making them very strong and high-melting. Polymers are large molecules made of repeating smaller units (monomers) joined by covalent bonds, forming long chains. They exhibit a wide range of properties depending on their structure and intermolecular forces. Metals consist of a lattice of positive metal ions surrounded by a 'sea' of delocalised electrons, which are responsible for their excellent electrical conductivity and malleability. The strength of metallic bonding gives metals high melting points.