Chemical compound

A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) composed of atoms from more than one element held together by chemical bonds. A chemical element bonded to an identical chemical element is not a chemical compound since only one element, not two different elements, is involved.

There are four types of compounds, depending on how the constituent atoms are held together:

A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using the standard abbreviations for the chemical elements, and subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H2O. Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service (CAS): its CAS number.

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.

2006-02-13 Drop-impact
Water-3D-balls
Pure water (H2O) is an example of a compound: the ball-and-stick model of the molecule (above) shows the spatial association of two parts hydrogen (white) and one part(s) oxygen (red)

Definitions

Any substance consisting of two or more different types of atoms (chemical elements) in a fixed stoichiometric proportion can be termed a chemical compound; the concept is most readily understood when considering pure chemical substances.[1]:15 [2][3] It follows from their being composed of fixed proportions of two or more types of atoms that chemical compounds can be converted, via chemical reaction, into compounds or substances each having fewer atoms.[4] The ratio of each element in the compound is expressed in a ratio in its chemical formula.[5] A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using the standard abbreviations for the chemical elements, and subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H2O. In the case of non-stoichiometric compounds, the proportions may be reproducible with regard to their preparation, and give fixed proportions of their component elements, but proportions that are not integral [e.g., for palladium hydride, PdHx (0.02 < x < 0.58)].[6]

Chemical compounds have a unique and defined chemical structure held together in a defined spatial arrangement by chemical bonds. Chemical compounds can be molecular compounds held together by covalent bonds, salts held together by ionic bonds, intermetallic compounds held together by metallic bonds, or the subset of chemical complexes that are held together by coordinate covalent bonds.[7] Pure chemical elements are generally not considered chemical compounds, failing the two or more atom requirement, though they often consist of molecules composed of multiple atoms (such as in the diatomic molecule H2, or the polyatomic molecule S8, etc.).[7] Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service (CAS): its CAS number.

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

Complexes

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.

London dispersion forces are the weakest force of all intermolecular forces. They are temporary attractive forces that form when the electrons in two adjacent atoms are positioned so that they create a temporary dipole. 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.[8]

A covalent bond, also known as a molecular bond, involves the sharing of electrons between two atoms. Primarily, this type of bond occurs between elements that fall close to each other on the periodic table of elements, yet it is observed between some metals and nonmetals. This is due to the mechanism of this type of bond. Elements that fall close to each other on the periodic table tend to have similar electronegativities, which means they have a similar affinity for electrons. Since neither element has a stronger affinity to donate or gain electrons, it causes the elements to share electrons so both elements have a more stable octet.

Ionic bonding occurs when valence electrons are completely transferred between elements. Opposite to covalent bonding, this chemical bond creates two oppositely charged ions. The metals in ionic bonding usually lose their valence electrons, becoming a positively charged cation. The nonmetal will gain the electrons from the metal, making the nonmetal a negatively charged anion. As outlined, ionic bonds occur between an electron donor, usually a metal, and an electron acceptor, which tends to be a nonmetal.[9]

Hydrogen bonding occurs when a hydrogen atom bonded to an electronegative atom forms an electrostatic connection with another electronegative atom through interacting dipoles or charges.[10][11][12][13]

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

References

  1. ^ Whitten, Kenneth W.; Davis, Raymond E.; Peck, M. Larry (2000), General Chemistry (6th ed.), Fort Worth, TX: Saunders College Publishing/Harcourt College Publishers, ISBN 978-0-03-072373-5
  2. ^ Brown, Theodore L.; LeMay, H. Eugene; Bursten, Bruce E.; Murphy, Catherine J.; Woodward, Patrick (2009), Chemistry: The Central Science, AP Edition (11th ed.), Upper Saddle River, NJ: Pearson/Prentice Hall, pp. 5–6, ISBN 978-0-13-236489-8, archived from the original on 2011-07-15
  3. ^ Hill, John W.; Petrucci, Ralph H.; McCreary, Terry W.; Perry, Scott S. (2005), General Chemistry (4th ed.), Upper Saddle River, NJ: Pearson/Prentice Hall, p. 6, ISBN 978-0-13-140283-6, archived from the original on 2009-03-22
  4. ^ Wilbraham, Antony; Matta, Michael; Staley, Dennis; Waterman, Edward (2002), Chemistry (1st ed.), Upper Saddle River, NJ: Pearson/Prentice Hall, p. 36, ISBN 978-0-13-251210-7
  5. ^ "Chemical compound". ScienceDaily. Archived from the original on 2017-09-13. Retrieved 2017-09-13.
  6. ^ Manchester, F. D.; San-Martin, A.; Pitre, J. M. (1994). "The H-Pd (hydrogen-palladium) System". Journal of Phase Equilibria. 15: 62–83. doi:10.1007/BF02667685. Phase diagram for Palladium-Hydrogen System
  7. ^ a b Atkins, Peter; Jones, Loretta (2004). Chemical Principles: The Quest for Insight.
  8. ^ "London Dispersion Forces". www.chem.purdue.edu. Archived from the original on 2017-01-13. Retrieved 2017-09-13.
  9. ^ "Ionic and Covalent Bonds". Chemistry LibreTexts. 2013-10-02. Archived from the original on 2017-09-13. Retrieved 2017-09-13.
  10. ^ Chemistry, International Union of Pure and Applied (2009). "Hydrogen bond". IUPAC Gold Book – hydrogen bond. goldbook.iupac.org. doi:10.1351/goldbook.H02899. ISBN 978-0-9678550-9-7. Archived from the original on 2017-07-09. Retrieved 2017-10-28.
  11. ^ "Hydrogen Bonds". chemistry.elmhurst.edu. Archived from the original on 2016-11-19. Retrieved 2017-10-28.
  12. ^ "Hydrogen Bonding". www.chem.purdue.edu. Archived from the original on 2011-08-08. Retrieved 2017-10-28.
  13. ^ "intermolecular bonding – hydrogen bonds". www.chemguide.co.uk. Archived from the original on 2016-12-19. Retrieved 2017-10-28.

Further reading

  • Robert Siegfried (2002), From elements to atoms: a history of chemical composition, American Philosophical Society, ISBN 978-0-87169-924-4
Agnuside

Agnuside is a chemical compound found in Vitex agnus-castus. Agnuside is the ester of aucubin and p-hydroxybenzoic acid.

Aroma compound

An aroma compound, also known as an odorant, aroma, fragrance, or flavor, is a chemical compound that has a smell or odor. A chemical compound has a smell or odor when it is sufficiently volatile to be transported to the olfactory system in the upper part of the nose.

Generally molecules meeting this specification have molecular weights of less than 300. Flavors affect both the sense of taste and smell, whereas fragrances affect only smell. Flavors tend to be naturally occurring, and fragrances tend to be synthetic.Aroma compounds can be found in food, wine, spices, floral scent, perfumes, fragrance oils, and essential oils. For example, many form biochemically during the ripening of fruits and other crops. In wines, most form as byproducts of fermentation. Also, many of the aroma compounds play a significant role in the production of flavorants, which are used in the food service industry to flavor, improve, and generally increase the appeal of their products.

An odorizer may add a detectable odor to a dangerous odorless substance, like propane, natural gas, or hydrogen, as a safety measure.

Aromaticity

In organic chemistry, the term aromaticity is used to describe a cyclic (ring-shaped), planar (flat) molecule with a ring of resonance bonds that exhibits more stability than other geometric or connective arrangements with the same set of atoms. Aromatic molecules are very stable, and do not break apart easily to react with other substances. Organic compounds that are not aromatic are classified as aliphatic compounds—they might be cyclic, but only aromatic rings have special stability (low reactivity).

Since the most common aromatic compounds are derivatives of benzene (an aromatic hydrocarbon common in petroleum and its distillates), the word aromatic occasionally refers informally to benzene derivatives, and so it was first defined. Nevertheless, many non-benzene aromatic compounds exist. In living organisms, for example, the most common aromatic rings are the double-ringed bases in RNA and DNA. An aromatic functional group or other substituent is called an aryl group.

The earliest use of the term aromatic was in an article by August Wilhelm Hofmann in 1855. Hofmann used the term for a class of benzene compounds, many of which have odors (aromas), unlike pure saturated hydrocarbons. Aromaticity as a chemical property bears no general relationship with the olfactory properties of such compounds (how they smell), although in 1855, before the structure of benzene or organic compounds was understood, chemists like Hofmann were beginning to understand that odiferous molecules from plants, such as terpenes, had chemical properties that we recognize today are similar to unsaturated petroleum hydrocarbons like benzene.

In terms of the electronic nature of the molecule, aromaticity describes a conjugated system often made of alternating single and double bonds in a ring. This configuration allows for the electrons in the molecule's pi system to be delocalized around the ring, increasing the molecule's stability. The molecule cannot be represented by one structure, but rather a resonance hybrid of different structures, such as with the two resonance structures of benzene. These molecules cannot be found in either one of these representations, with the longer single bonds in one location and the shorter double bond in another (see Theory below). Rather, the molecule exhibits bond lengths in between those of single and double bonds. This commonly seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds (cyclohexatriene), was developed by August Kekulé (see History below). The model for benzene consists of two resonance forms, which corresponds to the double and single bonds superimposing to produce six one-and-a-half bonds. Benzene is a more stable molecule than would be expected without accounting for charge delocalization.

Calcium oxide

Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term lime connotes calcium-containing inorganic materials, in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate. By contrast, quicklime specifically applies to the single chemical compound calcium oxide. Calcium oxide that survives processing without reacting in building products such as cement is called free lime.Quicklime is relatively inexpensive. Both it and a chemical derivative (calcium hydroxide, of which quicklime is the base anhydride) are important commodity chemicals.

Chemical substance

A chemical substance is a form of matter having constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be simple substances, chemical compounds, or alloys. Chemical elements may or may not be included in the definition, depending on expert viewpoint.Chemical substances are often called 'pure' to set them apart from mixtures. A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory. Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride) and refined sugar (sucrose). However, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical.

Chemical substances exist as solids, liquids, gases, or plasma, and may change between these phases of matter with changes in temperature or pressure. Chemical substances may be combined or converted to others by means of chemical reactions.

Forms of energy, such as light and heat, are not matter, and are thus not "substances" in this regard.

Empirical formula

In chemistry, the empirical formula of a chemical compound is the simplest positive integer ratio of atoms present in a compound. A simple example of this concept is that the empirical formula of sulphur monoxide, or SO, would simply be SO, as is the empirical formula of disulfur dioxide, S2O2. This means that sulfur monoxide and disulfur dioxide, both compounds of sulfur and oxygen, will have the same empirical formula. However, their chemical formulas, which express the number of atoms in each molecule of a chemical compound, may not be the same.

An empirical formula makes no mention of the arrangement or number of atoms. It is standard for many ionic compounds, like calcium chloride (CaCl2), and for macromolecules, such as silicon dioxide (SiO2).

The molecular formula, on the other hand, shows the number of each type of atom in a molecule. The structural formula shows the arrangement of the molecule. It is also possible for different types of compounds to have equal empirical formulas.

Samples are analyzed in specific elemental analysis tests to determine what percent of a particular element the sample is composed of.

Glabridin

Glabridin is a chemical compound that is found in the root extract of licorice (Glycyrrhiza glabra). Glabridin is an isoflavane, a type of isoflavonoid. This product is part of a larger family of plant-derived molecules, the natural phenols.

It is used as an ingredient in cosmetics and is listed in International Nomenclature of Cosmetic Ingredients (INCI).

Glabridin is yellowish-brown powder. It is insoluble in water, but soluble in organic solvents such as propylene glycol.

Inorganic compound

An inorganic compound is typically a chemical compound that lacks C-H bonds, that is, a compound that is not an organic compound, but the distinction is not defined or even of particular interest.Inorganic compounds comprise most of the Earth's crust, although the composition of the deep mantle remain active areas of investigation.Inorganic compounds can be defined as any compound that is not organic compound. Some simple compounds that contain carbon are often considered inorganic. Examples include carbon monoxide, carbon dioxide, carbonates, cyanides, cyanates, carbides, and thiocyanates. Many of these are normal parts of mostly organic systems, including organisms, which means that describing a chemical as inorganic does not obligately mean that it does not occur within living things.

Lime (material)

Lime is a calcium-containing inorganic mineral composed primarily of oxides, and hydroxide, usually calcium oxide and/ or calcium hydroxide. It is also the name for calcium oxide which occurs as a product of coal seam fires and in altered limestone xenoliths in volcanic ejecta. The word lime originates with its earliest use as building mortar and has the sense of sticking or adhering.These materials are still used in large quantities as building and engineering materials (including limestone products, cement, concrete, and mortar), as chemical feedstocks, and for sugar refining, among other uses. Lime industries and the use of many of the resulting products date from prehistoric times in both the Old World and the New World. Lime is used extensively for wastewater treatment with ferrous sulfate.

The rocks and minerals from which these materials are derived, typically limestone or chalk, are composed primarily of calcium carbonate. They may be cut, crushed, or pulverized and chemically altered. Burning (calcination) converts them into the highly caustic material quicklime (calcium oxide) and, through subsequent addition of water, into the less caustic (but still strongly alkaline) slaked lime or hydrated lime (calcium hydroxide, Ca(OH)2), the process of which is called slaking of lime. Lime kilns are the kilns used for lime burning and slaking.

When the term is encountered in an agricultural context, it usually refers to agricultural lime, which is crushed limestone, not a product of a lime kiln. Otherwise it most commonly means slaked lime, as the more dangerous form is usually described more specifically as quicklime or burnt lime.

Organic compound

In chemistry, an organic compound is generally any chemical compound that contains carbon. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Study of the properties and synthesis of organic compounds is the discipline known as organic chemistry. For historical reasons, a few classes of carbon-containing compounds (e.g., carbonates and cyanides), along with a handful of other exceptions (e.g., carbon dioxide), are not classified as organic compounds and are considered inorganic. No consensus exists among chemists on precisely which carbon-containing compounds are excluded, making the definition of an organic compound elusive. Although organic compounds only make up a small percentage of the Earth's crust, they are of central importance because all known life is based on organic compounds. Most synthetically produced organic compounds are ultimately derived from petrochemicals consisting mainly of hydrocarbons.

Potassium alum

Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the double sulfate of potassium and aluminium, with chemical formula KAl(SO4)2. It is commonly encountered as the dodecahydrate, KAl(SO4)2·12H2O. It crystallizes in cubic structure with space group P a -3 and lattice parameter of 12.18 Å. The compound is the most important member of the generic class of compounds called alums, and is often called simply alum.Potassium alum is commonly used in water purification, leather tanning, dyeing, fireproof textiles, and baking powder as E number E522. It also has cosmetic uses as a deodorant, as an aftershave treatment and as a styptic for minor bleeding from shaving.

Precursor (chemistry)

In chemistry, a precursor is a compound that participates in a chemical reaction that produces another compound.

In biochemistry, the term "precursor" often refers more specifically to a chemical compound preceding another in a metabolic pathway, such as a protein precursor.

Pteridine

Pteridine is an aromatic chemical compound composed of fused pyrimidine and pyrazine rings. A pteridine is also a group of heterocyclic compounds containing a wide variety of substitutions on this structure. Pterins and flavins are classes of substituted pteridines that have diverse biological roles.

Quinazolinone

Quinazolinone is a heterocyclic chemical compound, a quinazoline with a keto group. There are two structural isomers, 2-quinazolinone and 4-quinazolinone, with the 4-isomer being the more common.

Salt (chemistry)

In chemistry, a salt is an ionic compound that can be formed by the neutralization reaction of an acid and a base. Salts are composed of related numbers of cations (positively charged ions) and anions (negative ions) so that the product is electrically neutral (without a net charge). These component ions can be inorganic, such as chloride (Cl−), or organic, such as acetate (CH3CO−2); and can be monatomic, such as fluoride (F−), or polyatomic, such as sulfate (SO2−4).

Solasodamine

Solasodamine is a poisonous tetrasaccharide chemical compound of solasodine that occurs in plants of the Solanaceae family.

Solauricidine

Solauricidine is the poisonous aglycone chemical compound of the glycoalkaloid solauricine. It closely resembles an isomer of solasonine. Solauricidine occurs in plants of the Solanaceae family.

Solauricine

Solauricine is a poisonous glycoalkaloid chemical compound that occurs in plants of the Solanaceae family.

Wedelolactone

Wedelolactone is an organic chemical compound classified as a coumestan that occurs in Eclipta alba (false daisy) and in Wedelia calendulacea.

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