Chemical compound
The term "compound"—with a meaning similar to the modern—has been used at least since 1661 when Robert Boyle's The Sceptical Chymist was published.
[5] "Perfectly mixt bodies" included for example gold,[4] lead,[4] mercury,[2] and wine.
Quicksilver ... with Aqua fortis will be brought into a ... white Powder ... with Sulphur it will compose a blood-red and volatile Cinaber.
[7] Boyle used the concept of "corpuscles"—or "atomes",[8] as he also called them—to explain how a limited number of elements could combine into a vast number of compounds:If we assigne to the Corpuscles, whereof each Element consists, a peculiar size and shape ... such ... Corpuscles may be mingled in such various Proportions, and ... connected so many ... wayes, that an almost incredible number of ... Concretes may be compos’d of them.
Followers of Aristotle made Fire, Air, Earth and Water to be the four Elements, of which all earthly Things were compounded; and they suppos'd the Heavens to be a Quintessence, or fifth sort of Body, distinct from all these : But, since experimental Philosophy ... have been better understood, this Doctrine has been abundantly refuted.
The Chymists make Spirit, Salt, Sulphur, Water and Earth to be their five Elements, because they can reduce all terrestrial Things to these five : This seems to come nearer the Truth ; tho' they are not all agreed ...
There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, which require the fixed ratios.
It may be argued that they are related to, rather than being chemical compounds, insofar as the variability in their compositions is often due to either the presence of foreign elements trapped within the crystal structure of an otherwise known true chemical compound, or due to perturbations in structure relative to the known compound that arise because of an excess of deficit of the constituent elements at places in its structure; such non-stoichiometric substances form most of the crust and mantle of the Earth.
Ionic compounds containing basic ions hydroxide (OH−) or oxide (O2−) are classified as bases.
Ionic compounds can also be produced from their constituent ions by evaporation of their solvent, precipitation, freezing, a solid-state reaction, or the electron transfer reaction of reactive metals with reactive non-metals, such as halogen gases.
Ionic compounds typically have high melting and boiling points, and are hard and brittle.
As solids they are almost always electrically insulating, but when melted or dissolved they become highly conductive, because the ions are mobilized.
[20] A coordination complex consists of a central atom or ion, which is usually metallic and is called the coordination centre, and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents.
Additionally, London dispersion forces are responsible for condensing non polar substances to liquids, and to further freeze to a solid state dependent on how low the temperature of the environment is.
The metals in ionic bonding usually lose their valence electrons, becoming a positively charged cation.
