Chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element is therefore not a compound. A compound can be transformed into a different substance by a chemical reaction, which may involve interactions with other substances. In this process, bonds between atoms may be broken and/or new bonds formed.
There are four major types of compounds, distinguished by how the constituent atoms are bonded together.
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History of the concept
Robert Boyle
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. In this book, Boyle variously used the terms "compound",[2] "compounded body",[3] "perfectly mixt body",[4] and "concrete".[5] "Perfectly mixt bodies" included for example gold,[4] lead,[4] mercury,[2] and wine.[6] While the distinction between compound and mixture is not so clear, the distinction between element and compound is a central theme.
Quicksilver ... with Aqua fortis will be brought into a ... white Powder ... with Sulphur it will compose a blood-red and volatile Cinaber. And yet out of all these exotick Compounds, we may recover the very same running Mercury.[7]
Corpuscles of elements and compounds
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.[5]
Isaac Watts
In his Logick, published in 1724, the English minister and logician Isaac Watts gave an early definition of chemical element, and contrasted element with chemical compound in clear, modern terms.[9]
Among Substances, some are called Simple, some are Compound ... Simple Substances ... are usually called Elements, of which all other Bodies are compounded: Elements are such Substances as cannot be resolved, or reduced, into two or more Substances of different Kinds. ... 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 ... Compound Substances are made up of two or more simple Substances ... So a Needle is simple Body, being made only of Steel; but a Sword or a Knife is a compound because its ... Handle is made of Materials different from the Blade.
Definitions
Any substance consisting of two or more different types of
Chemical compounds have a unique and defined
There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, which require the fixed ratios. Many solid chemical substances—for example many silicate minerals—are chemical substances, but do not have simple formulae reflecting chemically bonding of elements to one another in fixed ratios; even so, these crystalline substances are often called "non-stoichiometric compounds". 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. Other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly.
Types
Molecules
A molecule is an
Ionic compounds
An ionic compound is a chemical compound composed of
4) and carbonate (CO2−
3) ions in ammonium carbonate. Individual ions within an ionic compound usually have multiple nearest neighbours, so are not considered to be part of molecules, but instead part of a continuous three-dimensional network, usually in a crystalline structure
Ionic compounds containing basic ions hydroxide (OH−) or oxide (O2−) are classified as bases. Ionic compounds without these ions are also known as salts and can be formed by acid–base reactions. 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
Intermetallic compounds
An intermetallic compound is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elements. Intermetallics are generally hard and brittle, with good high-temperature mechanical properties.[20][21][22] They can be classified as stoichiometric or nonstoichiometric intermetallic compounds.[20]
Complexes
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.[23][24][25] Many metal-containing compounds, especially those of transition metals, are coordination complexes.[26] A coordination complex whose centre is a metal atom is called a metal complex of d block element.
Bonding and forces
Compounds are held together through a variety of different types of bonding and forces. The differences in the types of bonds in compounds differ based on the types of elements present in the compound.
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Reactions
A compound can be converted to a different chemical composition by interaction with a second chemical compound via a chemical reaction. In this process, bonds between atoms are broken in both of the interacting compounds, and then bonds are reformed so that new associations are made between atoms. Schematically, this reaction could be described as AB + CD → AD + CB, where A, B, C, and D are each unique atoms; and AB, AD, CD, and CB are each unique compounds.
See also
- Chemical structure
- IUPAC nomenclature
- Dictionary of chemical formulas
- List of compounds
References
- PMID 31968937.
- ^ a b Boyle 1661, p. 41.
- ^ Boyle 1661, p. 13.
- ^ a b c Boyle 1661, p. 29.
- ^ a b Boyle 1661, p. 42.
- ^ Boyle 1661, p. 145.
- ^ Boyle 1661, p. 40-41.
- ^ Boyle 1661, p. 38.
- ^ Watts, Isaac (1726) [1724]. Logick: Or, the right use of reason in the enquiry after truth, with a variety of rules to guard against error in the affairs of religion and human life, as well as in the sciences. Printed for John Clark and Richard Hett. pp. 13–15.
- ISBN 978-0-03-072373-5
- ISBN 9781442559462, archivedfrom the original on 2021-05-31, retrieved 2020-12-08
- ISBN 978-0-13-140283-6, archivedfrom the original on 2009-03-22
- ISBN 978-0-13-251210-7
- ^ ISBN 978-0-7167-5701-6.
- ISBN 978-0-395-43302-7.
- ISBN 978-0-13-066997-1.
- ^ "Definition of molecule - NCI Dictionary of Cancer Terms". NCI. 2011-02-02. Retrieved 2022-08-26.
- ^ from the original on 2021-05-31. Retrieved 2020-11-10.
- from the original on 2021-05-31. Retrieved 2020-11-10.
- from the original on 2021-05-31. Retrieved 2020-11-10.
- ISBN 9780470687123.
- ISBN 978-0-08-037941-8.
- ^ "London Dispersion Forces". www.chem.purdue.edu. Archived from the original on 2017-01-13. Retrieved 2017-09-13.
- ^ "Ionic and Covalent Bonds". Chemistry LibreTexts. 2013-10-02. Archived from the original on 2017-09-13. Retrieved 2017-09-13.
- ^ "Hydrogen Bonding". www.chem.purdue.edu. Archived from the original on 2011-08-08. Retrieved 2017-10-28.
- ^ "intermolecular bonding – hydrogen bonds". www.chemguide.co.uk. Archived from the original on 2016-12-19. Retrieved 2017-10-28.
Sources
- Boyle, R. (1661). The Sceptical Chymist: or Chymico-Physical Doubts & Paradoxes, Touching the Spagyrist's Principles Commonly call'd Hypostatical; As they are wont to be Propos'd and Defended by the Generality of Alchymists. Whereunto is præmis'd Part of another Discourse relating to the same Subject. Printed by J. Cadwell for J. Crooke.
Further reading
- Robert Siegfried (1 October 2002), From elements to atoms: a history of chemical composition, American Philosophical Society, ISBN 978-0-87169-924-4