Chemical property

A chemical property is any of a material's properties that becomes evident during, or after, a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity.[1] Simply speaking, chemical properties cannot be determined just by viewing or touching the substance; the substance's internal structure must be affected greatly for its chemical properties to be investigated. When a substance goes under a chemical reaction, the properties will change drastically, resulting in chemical change. However, a catalytic property would also be a chemical property.

Chemical properties can be contrasted with physical properties, which can be discerned without changing the substance's structure. However, for many properties within the scope of physical chemistry, and other disciplines at the boundary between chemistry and physics, the distinction may be a matter of researcher's perspective. Material properties, both physical and chemical, can be viewed as supervenient; i.e., secondary to the underlying reality. Several layers of superveniency are possible.

Chemical properties can be used for building chemical classifications. They can also be useful to identify an unknown substance or to separate or purify it from other substances. Materials science will normally consider the chemical properties of a substance to guide its applications.

Examples

See also

References

  1. ^ William L. Masterton, Cecile N. Hurley, "Chemistry: Principles and Reactions", 6th edition. Brooks/Cole Cengage Learning, 2009, p.13 (Google books)
Ammelide

Ammelide (6-amino-2,4-dihydroxy-1,3,5-triazine) is a triazine and the hydrolysis product of ammeline.

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.

Biological activity

In pharmacology, biological activity or pharmacological activity describes the beneficial or adverse effects of a drug on living matter. When a drug is a complex chemical mixture, this activity is exerted by the substance's active ingredient or pharmacophore but can be modified by the other constituents. Among the various properties of chemical compounds, pharmacological/biological activity plays a crucial role since it suggests uses of the compounds in the medical applications. However, chemical compounds may show some adverse and toxic effects which may prevent their use in medical practice.

Activity is generally dosage-dependent. Further, it is common to have effects ranging from beneficial to adverse

for one substance when going from low to high doses. Activity depends critically on fulfillment of the ADME criteria. To be an effective drug, a compound not only must be active against a target, but also possess the appropriate ADME (Absorption, Distribution, Metabolism, and Excretion) properties necessary to make it suitable for use as a drug.Whereas a material is considered bioactive if it has interaction with or effect on any cell tissue in the human body, pharmacological activity is usually taken to describe beneficial effects, i.e. the effects of drug candidates as well as a substance's toxicity.

In the study of biomineralisation, bioactivity is often meant to mean the formation of calcium phosphate deposits on the surface of objects placed in simulated body fluid, a buffer solution with ion content similar to blood.

Chemicalize

Chemicalize is an online platform for chemical calculations, search, and text processing.

It is developed and owned by ChemAxon and offers various cheminformatics tools in freemium model: chemical property predictions, structure-based and text-based search, chemical text processing, and checking compounds with respect to national regulations of different countries.

Chirality (album)

Chirality is a solo piano album by American pianist John Burke. In an homage to Johann Sebastian Bach, Chirality used the chemical property of asymmetry as inspiration for melodies and mirrored countermelodies. After winning Jazz Album of the Year, Chirality became a finalist for Album of the Year at SoloPiano.com.

Cupiennin

Cupiennins are a group of small cytolytic peptides from the venom of the wandering spider Cupiennius salei. They are known to have high bactericidal, insecticidal and haemolytic activities. They are chemically cationic α-helical peptides. They were isolated and identified in 2002 as a family of peptides called cupiennin 1. The sequence was determined by a process called Edman degradation, and the family consists of cupiennin 1a, cupiennin 1b, cupiennin 1c, and cupiennin 1d. The amino acid sequences of cupiennin 1b, c, and d were obtained by a combination of sequence analysis and mass spectrometric measurements of comparative tryptic peptide mapping. Even though they are not strong toxins, they do enhance the effect of the spider venom by synergistically enhancing other components of the venom, such CSTX.

Electronegativity

Electronegativity, symbol χ, is a chemical property that describes the tendency of an atom to attract a shared pair of electrons (or electron density) towards itself. An atom's electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus. The higher the associated electronegativity number, the more an atom or a substituent group attracts electrons towards itself.

On the most basic level, electronegativity is determined by factors like the nuclear charge (the more protons an atom has, the more "pull" it will have on electrons) and the number/location of other electrons present in the atomic shells (the more electrons an atom has, the farther from the nucleus the valence electrons will be, and as a result the less positive charge they will experience—both because of their increased distance from the nucleus, and because the other electrons in the lower energy core orbitals will act to shield the valence electrons from the positively charged nucleus).

The opposite of electronegativity is electropositivity: a measure of an element's ability to donate electrons.

The term "electronegativity" was introduced by Jöns Jacob Berzelius in 1811,

though the concept was known even before that and was studied by many chemists including Avogadro.

In spite of its long history, an accurate scale of electronegativity was not developed until 1932, when Linus Pauling proposed an electronegativity scale, which depends on bond energies, as a development of valence bond theory. It has been shown to correlate with a number of other chemical properties. Electronegativity cannot be directly measured and must be calculated from other atomic or molecular properties. Several methods of calculation have been proposed, and although there may be small differences in the numerical values of the electronegativity, all methods show the same periodic trends between elements.

The most commonly used method of calculation is that originally proposed by Linus Pauling. This gives a dimensionless quantity, commonly referred to as the Pauling scale (χr), on a relative scale running from around 0.7 to 3.98 (hydrogen = 2.20). When other methods of calculation are used, it is conventional (although not obligatory) to quote the results on a scale that covers the same range of numerical values: this is known as an electronegativity in Pauling units.

As it is usually calculated, electronegativity is not a property of an atom alone, but rather a property of an atom in a molecule. Properties of a free atom include ionization energy and electron affinity. It is to be expected that the electronegativity of an element will vary with its chemical environment, but it is usually considered to be a transferable property, that is to say that similar values will be valid in a variety of situations.

Caesium is the least electronegative element in the periodic table (=0.79), while fluorine is most electronegative (=3.98). Francium and caesium were originally both assigned 0.7; caesium's value was later refined to 0.79, but no experimental data allows a similar refinement for francium. However, francium's ionization energy is known to be slightly higher than caesium's, in accordance with the relativistic stabilization of the 7s orbital, and this in turn implies that francium is in fact more electronegative than caesium.

Hydrophobe

In chemistry, hydrophobicity is the physical property of a molecule (known as a hydrophobe) that is seemingly repelled from a mass of water. (Strictly speaking, there is no repulsive force involved; it is an absence of attraction.) In contrast, hydrophiles are attracted to water.

Hydrophobic molecules tend to be nonpolar and, thus, prefer other neutral molecules and nonpolar solvents. Because water molecules are polar, hydrophobes do not dissolve well among them. Hydrophobic molecules in water often cluster together, forming micelles. Water on hydrophobic surfaces will exhibit a high contact angle.

Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar substances from polar compounds.Hydrophobic is often used interchangeably with lipophilic, "fat-loving". However, the two terms are not synonymous. While hydrophobic substances are usually lipophilic, there are exceptions, such as the silicones and fluorocarbons.

The term hydrophobe comes from the Ancient Greek ὑδρόφοβος, "having a horror of water", constructed from ὕδωρ, "water", and φόβος, "fear".

Journal of Physical and Chemical Reference Data

The Journal of Physical and Chemical Reference Data is a quarterly peer-reviewed scientific journal published by AIP Publishing on behalf of the National Institute of Standards and Technology. The objective of the journal is to provide critically evaluated physical and chemical property data, fully documented as to the original sources and the criteria used for evaluation, preferably with uncertainty analysis. The editors-in-chief are Donald R. Burgess, Jr, and Allan H. Harvey.

Lipophobicity

Lipophobicity, also sometimes called lipophobia (from the Greek λιποφοβία from λίπος lipos "fat" and φόβος phobos "fear"), is a chemical property of chemical compounds which means "fat rejection", literally "fear of fat". Lipophobic compounds are those not soluble in lipids or other non-polar solvents. From the other point of view, they do not absorb fats.

"Oleophobic" (from the Latin oleum "oil", Greek ελαιοφοβικό eleophobico from έλαιο eleo "oil" and φόβος phobos "fear") refers to the physical property of a molecule that is seemingly repelled from oil. (Strictly speaking, there is no repulsive force involved; it is an absence of attraction.)

The most common lipophobic substance is water.

Fluorocarbons are also lipophobic/oleophobic in addition to being hydrophobic.

Melam (chemistry)

Melam (N2-(4,6-diamino-1,3,5-triazin-2-yl)-1,3,5-triazine-2,4,6-triamine) is a condensation product of melamine.

Metal testing

Metal testing is a process or procedure used to check composition of an unknown metallic substance. There are destructive processes and nondestructive processes. Metal testing can also include, determining the properties of newly forged metal alloys. With many chemical-property databases readily available, identification of unmarked pure,common metals can be a quick and easy process. Leaving the original sample in complete, re-usable condition. This type of testing is nondestructive. When working with alloys (forged mixtures) of metals however, to determine the exact composition, could result in the original sample being separated into its starting materials, then measured and calculated. After the components are known they can be looked up and matched to known alloys. The original sample would be destroyed in the process. This type of testing is destructive.

Metamerism

Metamerism may refer to:

Metamerism (biology), in zoology and developmental biology, the property of having repeated segments, as in annelids

Metamerism (color), in colorimetry, a perceived matching of the colors that, based on differences in spectral power distribution, do not actually match

In chemistry, the chemical property of having the same proportion of atomic components in different arrangements (obsolete, replaced with isomer). In organic chemistry, compounds having the same molecular formula but different number of carbon atoms ( alkyl groups) on either side of functional group ( i.e., -O-,-S-, -NH-, -C(=O)-) are called metamers and the phenomenon is called metamerism.

Negativity

Negativity may refer to:

Negativity (quantum mechanics), a measure of quantum entanglement in quantum mechanics

Negative charge of electricity

Electronegativity, a chemical property pertaining to the ability to attract electrons

Positivity/negativity ratio, in behavioral feedback

Negativity effect, a psychological bias

Phenols

In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group (—OH) bonded directly to an aromatic hydrocarbon group. The simplest of the class is phenol, C6H5OH. Phenolic compounds are classified as simple phenols or polyphenols based on the number of phenol units in the molecule.

Phenols are synthesized industrially as well as naturally.

Physical property

A physical property is any property that is measurable, whose value describes a state of a physical system. The changes in the physical properties of a system can be used to describe its changes between momentary states. Physical properties are often referred to as observables. They are not modal properties. Quantifiable physical property is called physical quantity.

Physical properties are often characterized as intensive and extensive properties. An intensive property does not depend on the size or extent of the system, nor on the amount of matter in the object, while an extensive property shows an additive relationship. These classifications are in general only valid in cases when smaller subdivisions of the sample do not interact in some physical or chemical process when combined.

Properties may also be classified with respect to the directionality of their nature. For example, isotropic properties do not change with the direction of observation, and anisotropic properties do have spatial variance.

It may be difficult to determine whether a given property is a material property or not. Color, for example, can be seen and measured; however, what one perceives as color is really an interpretation of the reflective properties of a surface and the light used to illuminate it. In this sense, many ostensibly physical properties are called supervenient. A supervenient property is one which is actual, but is secondary to some underlying reality. This is similar to the way in which objects are supervenient on atomic structure. A cup might have the physical properties of mass, shape, color, temperature, etc., but these properties are supervenient on the underlying atomic structure, which may in turn be supervenient on an underlying quantum structure.

Physical properties are contrasted with chemical properties which determine the way a material behaves in a chemical reaction.

Quantitative structure–activity relationship

Quantitative structure–activity relationship models (QSAR models) are regression or classification models used in the chemical and biological sciences and engineering. Like other regression models, QSAR regression models relate a set of "predictor" variables (X) to the potency of the response variable (Y), while classification QSAR models relate the predictor variables to a categorical value of the response variable.

In QSAR modeling, the predictors consist of physico-chemical properties or theoretical molecular descriptors of chemicals; the QSAR response-variable could be a biological activity of the chemicals. QSAR models first summarize a supposed relationship between chemical structures and biological activity in a data-set of chemicals. Second, QSAR models predict the activities of new chemicals.Related terms include quantitative structure–property relationships (QSPR) when a chemical property is modeled as the response variable.

"Different properties or behaviors of chemical molecules have been investigated in the field of QSPR. Some examples are quantitative structure–reactivity relationships (QSRRs), quantitative structure–chromatography relationships (QSCRs) and, quantitative structure–toxicity relationships (QSTRs), quantitative structure–electrochemistry relationships (QSERs), and quantitative structure–biodegradability relationships (QSBRs)."As an example, biological activity can be expressed quantitatively as the concentration of a substance required to give a certain biological response. Additionally, when physicochemical properties or structures are expressed by numbers, one can find a mathematical relationship, or quantitative structure-activity relationship, between the two. The mathematical expression, if carefully validated can then be used to predict the modeled response of other chemical structures. A QSAR has the form of a mathematical model:

Activity = f(physiochemical properties and/or structural properties) + errorThe error includes model error (bias) and observational variability, that is, the variability in observations even on a correct model.

Radiation effect

Radiation effect is the physical and chemical property changes of materials induced by radiation.

Transferability (chemistry)

Transferability, in chemistry, is the assumption that a chemical property that is associated with an atom or a functional group in a molecule will have a similar (but not identical) value in a variety of different circumstances. Examples of transferable properties include:

Electronegativity

Nucleophilicity

Chemical shifts in NMR spectroscopy

Characteristic frequencies in Infrared spectroscopy

Bond length and bond angle

Bond energyTransferable properties are distinguished from conserved properties, which are assumed to always have the same value whatever the chemical situation, e.g. standard atomic weight.

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