Chemistry data and reference tables

Chemistry rests on a large body of measured and tabulated data that describes how matter is built and how it reacts. At the centre of this reference material is the periodic table, which arranges the chemical elements by increasing atomic number and groups them into columns whose members share similar properties. From the table follow many supporting values: atomic weights, electron configurations, ionization energies, electronegativities, and the standard states of the elements at room temperature.

Much of chemistry is concerned with structure at the scale of atoms and molecules. An atom consists of a small dense nucleus of protons and neutrons surrounded by electrons arranged in shells and orbitals. When atoms bond, they form molecules whose three-dimensional shapes can be represented by physical or computer molecular models. Organic molecules, built mainly around carbon, are described by structural formulas that show how the atoms are connected and by classifications into families such as alcohols, acids and hydrocarbons.

Reference databanks also cover the behaviour of substances in solution and in bulk. Acids and bases are characterised by the pH scale and by their dissociation constants. Electrochemistry tabulates standard electrode potentials that predict whether a reaction will proceed and how batteries and electrolysis cells behave. Crystallography records the ordered arrangements of atoms in solids and the symmetry of crystal lattices, while analytical methods such as chromatography separate mixtures so that their components can be identified and measured. Together these tables and databases let chemists predict properties, balance equations and interpret experimental results.

Frequently asked questions

What does the periodic table organise?

It arranges the elements by atomic number into rows (periods) and columns (groups), so that elements with similar chemical behaviour fall into the same group.

What is the pH scale?

pH is a measure of how acidic or basic a solution is, based on the concentration of hydrogen ions. Lower values are acidic, higher values are basic, and 7 is neutral.

What does chromatography do?

Chromatography separates the components of a mixture by how strongly each one interacts with a stationary phase as a mobile phase carries it along, allowing the parts to be identified.