Formal charge

In chemistry, a formal charge (FC) is the charge assigned to an atom in a molecule, assuming that electrons in all chemical bonds are shared equally between atoms, regardless of relative electronegativity.[1] When determining the best Lewis structure (or predominant resonance structure) for a molecule, the structure is chosen such that the formal charge on each of the atoms is as close to zero as possible.

The formal charge of any atom in a molecule can be calculated by the following equation:

where V is the number of valence electrons of the neutral atom in isolation (in its ground state); N is the number of non-bonding valence electrons on this atom in the molecule; and B is the total number of electrons shared in bonds with other atoms in the molecule.

Formal charge Principle V.1
Formal charges in ozone and the nitrate anion

Usage conventions

In organic chemistry convention, formal charges are an essential feature of a correctly rendered Lewis–Kekulé structure, and a structure omitting nonzero formal charges is considered incorrect, or at least, incomplete. In contrast, this convention is not followed in inorganic chemistry. Formal charges are drawn in close proximity to the atom bearing the charge. They may or may not be enclosed in a circle for clarity.

On the other hand, many workers in organometallic and a majority of workers in coordination chemistry will omit formal charges, unless they are needed for emphasis, or they are needed to make a particular point.[2] Instead a top-right corner ⌝ will be drawn following the covalently-bound, charged entity, in turn followed immediately by the overall charge.

Formal charge conventions
Three different depictions of the charges on trichloro(triphenylphosphine)palladium(1-). The first two follow "organic" convention, by showing formal charges. In the second structure, the L-type ligand is depicted with a coordinate or "dative" bond to avoid additional formal charges. The third structure follows "inorganic" convention, and only the total charge is given.

This difference in practice stems from the relatively straightforward assignment of bond order, valence electron count, and hence, formal charge for compounds only containing main-group elements (though oligomeric compounds like organolithium reagents and enolates tend to be depicted in an oversimplified and idealized manner), while there are genuine uncertainties, ambiguities, and outright disagreements when these assignments are attempted for transition-metal complexes.

Examples

  • Example: CO2 is a neutral molecule with 16 total valence electrons. There are three different ways to draw the Lewis structure
    • Carbon single bonded to both oxygen atoms (carbon = +2, oxygens = −1 each, total formal charge = 0)
    • Carbon single bonded to one oxygen and double bonded to another (carbon = +1, oxygendouble = 0, oxygensingle = −1, total formal charge = 0)
    • Carbon double bonded to both oxygen atoms (carbon = 0, oxygens = 0, total formal charge = 0)

Even though all three structures gave us a total charge of zero, the final structure is the superior one because there are no charges in the molecule at all.

Pictorial method

The following is equivalent:

  • Draw a circle around the atom for which the formal charge is requested (as with carbon dioxide, below)
Ls1
Ls1
  • Count up the number of electrons in the atom's "circle." Since the circle cuts the covalent bond "in half," each covalent bond counts as one electron instead of two.
  • Subtract the number of electrons in the circle from the group number of the element (the Roman numeral from the older system of group numbering, NOT the IUPAC 1-18 system) to determine the formal charge.
Ls3a
Ls3a
  • The formal charges computed for the remaining atoms in this Lewis structure of carbon dioxide are shown below.
Ls4
Ls4

It is important to keep in mind that formal charges are just that – formal, in the sense that this system is a formalism. The formal charge system is just a method to keep track of all of the valence electrons that each atom brings with it when the molecule is formed.

Formal charge compared to oxidation state

Formal charge is a tool for estimating the distribution of electric charge within a molecule.[1] The concept of oxidation states constitutes a competing method to assess the distribution of electrons in molecules. If the formal charges and oxidation states of the atoms in carbon dioxide are compared, the following values are arrived at:

Co2comp
Co2comp

The reason for the difference between these values is that formal charges and oxidation states represent fundamentally different ways of looking at the distribution of electrons amongst the atoms in the molecule. With formal charge, the electrons in each covalent bond are assumed to be split exactly evenly between the two atoms in the bond (hence the dividing by two in the method described above). The formal charge view of the CO2 molecule is essentially shown below:

Co2-1
Co2-1

The covalent (sharing) aspect of the bonding is overemphasized in the use of formal charges, since in reality there is a higher electron density around the oxygen atoms due to their higher electronegativity compared to the carbon atom. This can be most effectively visualized in an electrostatic potential map.

With the oxidation state formalism, the electrons in the bonds are "awarded" to the atom with the greater electronegativity. The oxidation state view of the CO2 molecule is shown below:

Co2-2
Co2-2

Oxidation states overemphasize the ionic nature of the bonding; the difference in electronegativity between carbon and oxygen is insufficient to regard the bonds as being ionic in nature.

In reality, the distribution of electrons in the molecule lies somewhere between these two extremes. The inadequacy of the simple Lewis structure view of molecules led to the development of the more generally applicable and accurate valence bond theory of Slater, Pauling, et al., and henceforth the molecular orbital theory developed by Mulliken and Hund.

See also

References

  1. ^ a b Hardinger, Steve. "Formal Charges" (PDF). University of California, Los Angeles. Retrieved 11 March 2016.
  2. ^ "Chapter 48, Organometallic Chemistry". Organic chemistry. Clayden, Jonathan. Oxford: Oxford University Press. 2001. pp. 1311–1314. ISBN 0198503474. OCLC 43338068.CS1 maint: others (link)
2-Heptanone

2-Heptanone, also known as methyl n-amyl ketone, or Heptan-2-one, is a ketone with the molecular formula C7H14O. It is a colorless, water-like liquid with a banana-like, fruity odor. 2-Heptanone has a neutral formal charge, and is only slightly soluble in water.

2-Heptanone is listed by the FDA as a "food additive permitted for direct addition to food for human consumption" (21 CFR 172.515), and it occurs naturally in certain foods (e.g., beer, white bread, butter, various cheeses and potato chips).The mechanism of action of 2-heptanone as a pheromone at odorant receptors in rodents has been investigated. 2-Heptanone is present in the urine of stressed rats and believe that it is used as a means to alert other rats. Certain species of worms are attracted to 2-heptanone and bacteria can use this as a means of parthenogenesis. 2-Heptanone has also been found to be excreted by honey bees when they bite small pests within the colony such as wax moth larvae and Varroa mites. Though it was historically believed to be an alarm pheromone, 2-heptanone has been shown to act as an anaesthetic on the pests, enabling the honey bee to stun the pest and eject it from the hive. The work could lead to the use of 2-heptanone as an alternative local anaesthetic to lidocaine, which although well established for clinical use, has the disadvantage of provoking allergic reactions in some people.2-Heptanone was one of the metabolites of n-heptane found in the urine of employees exposed to heptane in shoe and tire factories. This commonly occurs from exposure to plasticisers. 2-Heptanone can be absorbed through the skin, inhaled and consumed. Exposure to 2-Heptanone can cause irritation of skin/eyes, respiratory system, headaches, vomiting, and nausea.

Alprenoxime

Alprenoxime is a beta blocker. It is a prodrug to alprenolol.

Ate complex

An ate complex in chemistry is a salt formed by the reaction of a Lewis acid with a Lewis base whereby the central atom (from the Lewis acid) increases its valence and gains a negative formal charge. (Note that in this definition the meaning of valence is equivalent to coordination number). Often in chemical nomenclature the phrase ate is suffixed to the element in question. For example, the ate complex of a boron compound is called a borate. Thus trimethylborane and methyllithium react to form the ate compound Me4B−Li+, lithium tetramethylborate(1-). This concept was introduced by Georg Wittig in 1958. Ate complexes are common for metals, including the transition metals (groups 3-11), as well as the metallic or semi-metallic elements of group 2, 12, 13. They are also well-established for third-period or heavier elements of groups 14-18 in their higher oxidation states.

Ate complexes are the dual counterparts to onium compounds.

Lewis acids form ate ions when the central atom reacts with a donor (2 e– X-type ligand), gaining one more bond and becoming a negative-charged anion.

Lewis bases form onium ions when the central atom reacts with an acceptor (0 e– Z-type ligand), gaining one more bond and becoming a positive-charged cation.

Calixto Martínez

Calixto Martínez Arias is an independent Cuban journalist, who was jailed by the Cuban government from September 16, 2012 to April 9, 2013 without formal charge. He had been reporting about new outbreak of cholera at the east of the island, while the Cuban government officially claimed that after a short summer period in 2012 the illness was already eradicated. He also discovered 5 tons of humanitarian aid sent to Cuba by World Health Organization (WHO), which was left to spoil at Havana's airport.

Martínez was accused of disrespect to former leader of the country Fidel Castro and his brother, president Raúl Castro. He thus faces up to three years in prison, as was pointed out by Reporters without borders.The Cuban government admitted the outbreak of cholera on the island on July 13, 2012, but already on August 28, 2012 stated the illness was eradicated. 417 cases and 3 fatalities were officially reported. In the middle of January 2013, after the rise of cholera cases in Havana, the government officially acknowledged the illness was back.At the end of January 2013, Amnesty International named Martínez a prisoner of conscience and called for his immediate release. He was released on April 9, 2013, having never been formally charged.

Carbenium ion

A carbenium ion is a positive ion with the structure RR′R″C+, that is, a chemical species with a trivalent carbon that bears a +1 formal charge.

In older literature the name carbonium ion was used for this class, but now it refers exclusively to another family of carbocations, the carbonium ions, where the charged carbon is pentavalent. The current definitions were proposed by the chemist George Andrew Olah in 1972, and are now widely accepted.

Carbenium ions are generally highly reactive due to having an incomplete octet of electrons; however, certain carbenium ions, such as the tropylium ion, are relatively stable due to the positive charge being delocalised between the carbon atoms.

Chemical classification

Chemical classification systems attempt to classify elements or compounds according to certain chemical functional or structural properties. Whereas the structural properties are largely intrinsic, functional properties and the derived classifications depend to a certain degree on the type of chemical interaction partners on which the function is exerted. Sometimes other criteria like purely physical ones (e.g. molecular weight) or - on the other hand - functional properties above the chemical level are also used for building chemical taxonomies.

Some systems mix the various levels, resulting in hierarchies where the domains are slightly confused, for example having structural and functional aspects end up on the same level. Whereas chemical function is closely dependent on chemical structure, the situation becomes more involved when e.g. pharmacological function is integrated, because the QSAR can usually not be directly computed from structural qualities.

Chemical polarity

In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end.

Polar molecules must contain polar bonds due to a difference in electronegativity between the bonded atoms. A polar molecule with two or more polar bonds must have a geometry which is asymmetric in at least one direction, so that the bond dipoles do not cancel each other.

Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Polarity underlies a number of physical properties including surface tension, solubility, and melting and boiling points.

Cobalt(III) chloride

Cobalt(III) chloride or cobaltic chloride is an unstable and elusive compound of cobalt and chlorine with formula CoCl3. In this compound, the cobalt atoms have a formal charge of +3.The compound has been reported to exist in the gas phase at high temperatures, in equilibrium with cobalt(II) chloride and chlorine gas. It has also been found to be stable at very low temperatures, dispersed in a frozen argon matrix.Some articles from the 1920s and 1930s claim the synthesis of bulk amounts of this compound in pure form; however, those results do not seem to have been reproduced, or have been attributed to other substances like the hexachlorocobaltate(III) anion CoCl3−6. Those earlier reports claim that it gives green solutions in anhydrous solvents such as ethanol and diethyl ether, and that it is stable only a very low temperatures (below −60 °C).

Distonic ion

Distonic ions are chemical species that contain two ionic charges on the same molecule separated by two or more carbon or heteroatoms. Distonic radical ions are unique due to the fact that its charges and radical sites are in different locations (on separate atoms ), unlike regular radicals where the formal charge and unpaired electron are in the same location. These molecular species are created when ionization takes place with either zwitterions or diradicals; ultimately, a neutral molecule loses an electron. Through experimental research distonic radicals have been found to be extremely stable gas phase ions and can be separated into different classes depending on the inherent features of the charged portion of the ion.

Edgar Foshee

Sergeant Major Edgar Foshee, a devout anti-communist, served as a combat medic in the U.S. Army Special Forces. His former wife Thuong Nguyen Cuc Foshee was held without formal charge by the government of Vietnam starting in September 2005. She was eventually convicted of terrorism and returned to the United States in November 2006 after her early release for medical problems.

Lewis structure

Lewis structures, also known as Lewis dot diagrams, Lewis dot formulas, Lewis dot structures, electron dot structures, or Lewis electron dot structures (LEDS), are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. A Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds. The Lewis structure was named after Gilbert N. Lewis, who introduced it in his 1916 article The Atom and the Molecule. Lewis structures extend the concept of the electron dot diagram by adding lines between atoms to represent shared pairs in a chemical bond.

Lewis structures show each atom and its position in the structure of the molecule using its chemical symbol. Lines are drawn between atoms that are bonded to one another (pairs of dots can be used instead of lines). Excess electrons that form lone pairs are represented as pairs of dots, and are placed next to the atoms.

Although main group elements of the second period and beyond usually react by gaining, losing, or sharing electrons until they have achieved a valence shell electron configuration with a full octet of (8) electrons, hydrogen (H) can only form bonds which share just two electrons.

Nitrate

Nitrate is a polyatomic ion with the molecular formula NO−3 and a molecular mass of 62.0049 u. Organic compounds that contain the nitrate ester as a functional group (RONO2) are also called nitrates.

Preferred charge

A preferred charge is an interim step in the United States' military justice system.According to Jonathon Turley, a law professor at George Washington University, testifying before the Senate Intelligence Committee, the US military justice system equivalent of a formal charge is only leveled following the recommendation of an article 32 hearing -- a hearing held under the authority of article 32 of the Uniform Code of Military Justice.

Propadienone

Propadienone is an organic compound with molecular formula C3H2O consisting of a Propadiene carbon framework with a ketone functional group. Structure of propadienone is not the same as propadiene of Carbon suboxide. In propadienone, Oxygen has +1 formal charge and C2 caron has -1 formal charge.

PubChem

PubChem is a database of chemical molecules and their activities against biological assays. The system is maintained by the National Center for Biotechnology Information (NCBI), a component of the National Library of Medicine, which is part of the United States National Institutes of Health (NIH). PubChem can be accessed for free through a web user interface. Millions of compound structures and descriptive datasets can be freely downloaded via FTP. PubChem contains substance descriptions and small molecules with fewer than 1000 atoms and 1000 bonds. More than 80 database vendors contribute to the growing PubChem database.

Sulfite

Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), SO2−3. The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are widely used.

Sulfites are substances that naturally occur in some foods and the human body. They are also used as regulated food additives.

Thuong Nguyen Cuc Foshee

Thuong Nguyen Cuc Foshee is a Vietnamese American who was held without formal charge by the government of Vietnam after her arrest in September 2005 on accusations of plotting to broadcast anti-communist radio messages under the direction of Government of Free Vietnam (GFVN), an anti-government group. She is divorced from GFVN representative Edgar Foshee. Their daughter Elizabeth McCausland, a lawyer, actively campaigned for her mother's freedom politically through United States government officials. Ms. Foshee was ultimately arrested and charged with conducting terrorist activities and went on trial November 10, 2006. She, along with six other defendants, was convicted and sentenced to 15 months with credit for time served.

Trisulfur

The S3 molecule or trisulfur or sulfur trimer or thiozone or triatomic sulfur is an allotrope of sulfur. It occurs as a mixture in liquid and gaseous sulfur and also at cryogenic temperatures as a solid. Under standard conditions it is unstable and self reacts to solid sulfur cyclooctasulfur. The molecule shape is similar to that of ozone. S3 is found in sulfur vapour, comprising 10% of vapour species at 713 K (440 °C; 824 °F) and 1,333 Pa (10.00 mmHg; 0.1933 psi). It is cherry red in colour, with a bent structure, similar to ozone, O3. The bonds between the atoms are not full double bonds (as this would require two fewer electrons, similar to carbon disulfide), and the molecule can be thought of as a resonance between two states, in each of which one of the end atoms has a negative formal charge while the central atom has a positive formal charge, making it valence isoelectronic to ozone.

The molecule has a distance between sulfur atoms of 191.70 ± .01 pm (1.9170 ± 0.0001 Å) and angle at the central atom of 117.36°±0.006°. However, cyclic S3, where the sulfur atoms are arranged in an equilateral triangle with three bonds (similar to cyclic ozone), should in theory be lower in energy than the bent structure actually observed.The name thiozone was invented by Hugo Erdmann in 1908 who hypothesized that S3 made up a large proportion of liquid sulfur. However its existence was unproven until the experiments of J. Berkowitz in 1964.

Using mass spectrometry, he showed that sulfur vapour contains the S3 molecule. Above 1,200 °C (2,190 °F) S3 is the second most common molecule after S2 in sulfur gas. In liquid sulfur the molecule is not common until the temperature is high, such as 500 °C (932 °F). However, small molecules like this contribute to most of the reactivity of liquid sulfur. S3 has an absorption peak of 425 nm with a tail extending into blue light.S3 can also be made by photolysis of S3Cl2 embedded in a glass or matrix of solid noble gas.

Valence (chemistry)

In chemistry, the valence or valency of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules. The concept of valence was developed in the second half of the 19th century and helped successfully explain the molecular structure of inorganic and organic compounds.

The quest for the underlying causes of valence led to the modern theories of chemical bonding, including the cubical atom (1902), Lewis structures (1916), valence bond theory (1927), molecular orbitals (1928), valence shell electron pair repulsion theory (1958), and all of the advanced methods of quantum chemistry.

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