Elements, compounds and mixtures Study Guide

Elements are broadly classified into metals and non-metals based on their characteristic physical and chemical properties. These differences arise from their atomic structures, particularly the number of electrons in their outer shells and their tendency to gain, lose, or share electrons during chemical reactions. Metals, typically found on the left and centre of the Periodic Table, are generally shiny solids at room temperature (except mercury, which is a liquid). They are good conductors of heat and electricity, are malleable (can be hammered into sheets), and ductile (can be drawn into wires). Chemically, metals tend to lose their outer shell electrons to form positive ions in reactions. Non-metals, found on the right side of the Periodic Table, exhibit a wider range of physical states at room temperature (solids, liquids, gases). They are typically dull, brittle if solid, and poor conductors of heat and electricity (insulators), with the exception of graphite, which conducts electricity. Chemically, non-metals tend to gain or share electrons to achieve a full outer shell, forming negative ions or covalent bonds respectively. This fundamental distinction in electron behaviour dictates their reactivity and the types of compounds they form, influencing their everyday uses.

Chromatography is a powerful analytical technique used to separate mixtures. The fundamental principle behind all chromatographic separations relies on the differential distribution of components within a mixture between two phases: a stationary phase and a mobile phase. The stationary phase is a fixed material, such as paper or a solid packed into a column. The mobile phase is a fluid (either a liquid or a gas) that moves through the stationary phase, carrying the components of the mixture with it.

When a mixture is introduced into the chromatography system, its components begin to interact with both the stationary and mobile phases. Substances that have a stronger affinity (attraction) for the stationary phase will spend more time adsorbed or absorbed onto it, moving more slowly. Conversely, substances with a stronger affinity for the mobile phase will dissolve or travel within it more readily, moving through the system faster. This difference in affinity causes the components of the mixture to travel at different speeds, leading to their separation.

The degree of separation achieved depends on the differing solubilities (for liquid mobile phases), differing boiling points (for gas mobile phases), or differing adsorptive properties of the components with respect to both phases. In essence, chromatography allows scientists to separate and identify the individual components of a complex mixture based on their unique distribution and partitioning between these two distinct phases.