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# Electropositive Radicals with their Valency

We know that elements and compounds are pure substances. An element cannot be decomposed into simpler substances. They are listed in the periodic table. Each element can represent by elemental symbols such as Ca for calcium, N for nitrogen, K for potassium etc. Similarly a compound is considered to be a pure substance which can be further broken into simpler substances as it is composed of two or more elements.

Elements cannot be decomposed into any further simpler substances.  In the elemental symbol, the 2nd letter in the symbol is a lower case letter such as ‘He’ for helium, ‘Ca’ for calcium, ‘Ne’ for neon. They can be in solid, liquid or gaseous state such as mercury (Hg), bromine (Br) and hydrogen (H). The charge on element forms electropositive or electronegative radicals. Radicals can be an atom or group of atom with some charge. A simple radical is composed of one atom while a compound radical is formed by the groups of atom. On the basis of charge on radical, they can be classified as electropositive and electronegative radicals.

An electropositive radical has positive charge while an electronegative radical has negative charge on it. The charge or valency of the radicals represents the combining capacity of the radicals. For example the valency of hydrogen atoms is one, it means that it can combine or displace one atom of the element and form a compound. Some common examples of it are hydrogen chloride [HCl], nitric acid [HNO3] and hydrofluoric acid [HF]. In sulphuric acid molecule, the valency of the sulphate radical is 2. Overall valency can be defined as the number of electrons which can donates or accepts by an atom to get the duplet state or octet state in its valence shell.

Valency of a radical is always a whole number. On the basis of valency, elements or radicals can be classified as monovalent (valency=1), divalent (valency=2), trivalent (valency=3) and so on. All metals form electropositive radicals while all non-metals form electronegative radicals

The charge on the radicals is due to lose or gain of electrons to get the stable valence shell configuration. The radicals with opposite charges attract each other to form electrovalent compounds which are also called as ionic compounds. The cation or electropositive radicals form ionic bond with electronegative radicals to form ionic compounds.

Since metals have tendency to lose electrons therefore they can easily form electropositive radicals such as Na+, Fe3+, Mn7+ etc. The charge on electropositive radicals depends on the valence shell configuration of elements. For example; alkali metals have one electron in their valence shell therefore they form 1+ ions while alkaline earth metals have 2 electrons in their valence shell and form M2+ radicals. The d-block elements can show variable valency due to incomplete d-orbitals.

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Electronegativity

Electronegativity, symbol Ï‡ (the Greek letter chi), is a chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself and thus the tendency to form negative ions. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus. The higher the associated electronegativity number, the more an element or compound attracts electrons towards it. First proposed by Linus Pauling in 1932 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 Pauling. This gives a dimensionless quantity, commonly referred to as the Pauling scale, on a relative scale running from around 0.7 to 3.98 (hydrogen&nbsp;= 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.

Electronegativity, as it is usually calculated, is not strictly an atomic property, but rather a property of an atom in a molecule: the equivalent property of a free atom is its 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.
The opposite of electronegativity is electropositivity: a measure of an element's ability to donate electrons.

## Electronegativities of the elements

Periodic table of electronegativity using the Pauling scale

## Methods of calculation

### Pauling electronegativity

Pauling first proposed the concept of electronegativity in 1932 as an explanation of the fact that the covalent bond between two different atoms (Aâ€“B) is stronger than would be expected by taking the average of the strengths of the Aâ€“A and Bâ€“B bonds. According to valence bond theory, of which Pauling was a notable proponent, this "additional stabilization" of the heteronuclear bond is due to the contribution of ionic canonical forms to the bonding.

The difference in electronegativity between atoms A and B is given by:

\chi_{\rm A} - \chi_{\rm B} = ({\rm eV})^{-1/2} \sqrt{E_{\rm d}({\rm AB}) - [E_{\rm d}({\rm AA}) + E_{\rm d}({\rm BB})]/2}

where the dissociation energies, Ed, of the Aâ€“B, Aâ€“A and Bâ€“B bonds are expressed in electronvolts, the factor (eV)â€“Â½ being included to ensure a dimensionless result. Hence, the difference in Pauling electronegativity between hydrogen and bromine is 0.73 (dissociation energies: Hâ€“Br, 3.79&nbsp;eV; Hâ€“H, 4.52&nbsp;eV; Brâ€“Br 2.00&nbsp;eV)

As only differences in electronegativity are defined, it is necessary to choose an arbitrary reference point in order to construct a scale. Hydrogen was chosen as the reference, as it forms covalent bonds with a large variety of elements: its electronegativity was fixed first at 2.1, later revised to 2.20. It is also necessary to decide which of the two elements is the more electronegative (equivalent to choosing one of the two possible signs for the square root). This is done by "chemical intuition": in the above example, hydrogen bromide dissolves in water to form H+ and Brâ€“ ions, so it may be assumed that bromine is more electronegative than hydrogen.

To calculate Pauling electronegativity for an element, it is necessary to have data on the dissociation energies of at least two types of covalent bond formed by that element. Allred updated Pauling's original values in 1961 to take account of the greater availability of thermodynamic data, and it is these "revised Pauling" values of the electronegativity which are most usually used.

### Mulliken electronegativity

Mulliken proposed that the arithmetic mean of the first ionization energy and the electron affinity should be a measure of the tendency of an atom to attract electrons. As this definition is not dependent on an arbitrary relative scale, it has also been termed absolute electronegativity, with the units of kilojoules per mole or electronvolts.

However, it is more usual to use a linear transformation to transform these absolute values into values which resemble the more familiar Pauling values. For ionization energies and electron affinities in electronvolts,

\chi = 0.187(E_{\rm i} + E_{\rm ea}) + 0.17 \,

and for energies in kilojoules per mole,

\chi = (1.97\times 10^{-3})(E_{\rm i} + E_{\rm ea}) + 0.19.

The Mulliken electronegativit

Carbene

In chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is RR'C:, but the carbon can instead be double-bonded to one group. The term "carbene" may also merely refer to the compound H2C:, also called methylene, the parent hydride to which all other carbene compounds are related. Carbenes are classified as either singlets or triplets depending upon their electronic structure. Most carbenes are very short lived, although persistent carbenes are known.

One well studied carbene is Cl2C:, or dichlorocarbene, which can be generated in situfromchloroform and a strong base.

## Structure and bonding

The two classes of carbenes are singlet and triplet carbenes. Singlet carbenes are spin-paired. In the language of valence bond theory, the molecule adopts an sp2hybrid structure. Triplet carbenes have two unpaired electrons. They may be either linear or bent, i.e. sp or sp2 hybridized, respectively. Most carbenes have a nonlinear triplet ground state, except for those with nitrogen, oxygen, or sulfur atoms, and halides directly bonded to the divalent carbon.

Carbenes are called singlet or triplet depending on the electronic spins they possess. Triplet carbenes are paramagnetic and may be observed by electron spin resonance spectroscopy if they persist long enough. The total spin of singlet carbenes is zero while that of triplet carbenes is one (in units of \hbar). Bond angles are 125-140Â° for triplet methylene and 102Â° for singlet methylene (as determined by EPR). Triplet carbenes are generally stable in the gaseous state, while singlet carbenes occur more often in aqueous media.

For simple hydrocarbons, triplet carbenes usually have energies 8 kcal/mol (33 kJ/mol) lower than singlet carbenes (see also Hund's rule of Maximum Multiplicity), thus, in general, triplet is the more stable state (the ground state) and singlet is the excited state species. Substituents that can donate electron pairs may stabilize the singlet state by delocalizing the pair into an empty p-orbital. If the energy of the singlet state is sufficiently reduced it will actually become the ground state. No viable strategies exist for triplet stabilization. The carbene called 9-fluorenylidene has been shown to be a rapidly equilibrating mixture of singlet and triplet states with an approximately 1.1 kcal/mol (4.6 kJ/mol) energy difference. It is however debatable whether diaryl carbenes such as the fluorene carbene are true carbenes because the electrons can delocalize to such an extent that they become in fact biradicals. In silico experiments suggest that triplet carbenes can be stabilized with electropositive groups such as trifluorosilyl groups.

## Reactivity

Singlet and triplet carbenes exhibit divergent reactivity. Singlet carbenes generally participate in cheletropic reactions as either electrophiles or nucleophiles. Singlet carbenes with unfilled p-orbital should be electrophilic. Triplet carbenes can be considered to be diradicals, and participate in stepwise radical additions. Triplet carbenes have to go through an intermediate with two unpaired electrons whereas singlet carbene can react in a single concerted step.

Due to these two modes of reactivity, reactions of singlet methylene are stereospecific whereas those of triplet methylene are stereoselective. This difference can be used to probe the nature of a carbene. For example, the reaction of methylene generated from photolysis of diazomethane with cis-2-butene or with trans-2-butene each give a single diastereomer of the 1,2-dimethylcyclopropane product: cis from cis and trans from trans, which proves that the methylene is a singlet. If the methylene were a triplet, one would not expect the product to depend upon the starting alkene geometry, but rather a nearly identical mixture in each case.

Reactivity of a particular carbene depends on the substituent groups. Their reactivity can be affected by metals. Some of the reactions carbenes can do are insertions into C-H bonds, skeletal rearrangements, and additions to double bonds. Carbenes can be classified as nucleophilic, electrophilic, or ambiphilic. For example, if a

Unpaired electron - Wikipedia, the free encyclopedia

Radicals are uncommon in s- and p-block chemistry, since the unpaired electron occupies a valence p orbital or an sp, sp2 or sp3 hybrid orbital. ...

Nitrogen group

The nitrogen group is a periodic table group consisting of nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi) and ununpentium (Uup) (unconfirmed).

In modern IUPAC notation, it is called Group 15. In the old IUPAC and CAS systems, it was called Group VB and Group VA, respectively (pronounced "group five B" and "group five A", because "V" is a Roman numeral). In the field of semiconductor physics, it is still universally called Group V. It is also collectively named the pnictogens. The "five" ("V") in the historical names comes from the fact that these elements have five valence electrons (see below).

Like other groups, the members of this family show patterns in its electron configuration, especially the outermost shells resulting in trends in chemical behavior:

This group has the defining characteristic that all the component elements have 5 electrons in their outermost shell, that is 2 electrons in the s subshell and 3 unpaired electrons in the p subshell. They are therefore 3 electrons short of filling their outermost electron shell in their non-ionized state. The most important element of this group is nitrogen(chemical symbolN), which in its diatomic form is the principal component of air.

Binary compounds of the group can be referred to collectively as pnictides. The spelling derives from the GreekÏ€Î½Î¯Î³ÎµÎ¹Î½ (pnigein), to choke or stifle, which is a property of nitrogen; they are also mnemonic for the two most common members, P and N. The name pentels (from the Latin penta, five) was also used for this group at one time, stemming from the earlier group naming convention (Group VB).

These elements are also noted for their stability in compounds due to their tendency for forming double and triple covalent bonds. This is the property of these elements which leads to their potential toxicity, most evident in phosphorus, arsenic and antimony. When these substances react with various chemicals of the body, they create strong free radicals not easily processed by the liver, where they accumulate. Paradoxically it is this strong bonding which causes nitrogen and bismuth's reduced toxicity (when in molecules), as these form strong bonds with other atoms which are difficult to split, creating very unreactive molecules. For example N2, the diatomic form of nitrogen, is used for inert atmosphere in situations where argon or another noble gas would be prohibitively expensive.

The nitrogen group consists of two non-metals, two metalloids, one metal, and one synthetic (presumably metallic) element. All the elements in the group are a solid at room temperature except for nitrogen which is a gas at room temperature. Nitrogen and bismuth, despite both being part of the nitrogen group, are very different in their physical properties. For example, at STP nitrogen is a transparent nonmetallic gas, while bismuth is a brittle pinkish metallic solid.

Question:

Answers:Here are couple of answers from internet but any good Chemistry text book will have all this information. Look up one from a library if you do not have one: http://home.att.net/~cat6a/class_elem-VI.htm http://www.syvum.com/cgi/online/serve.cgi/squizzes/chem/valency2a.html

Question:and i dont want it in the periodic table form i want it as a list of elements and radicals with their valencies alongwith their atomic no. , mass no., electronic configuration, and of course, their symbols.

Answers:here its inter active or color coded and expanded wow for all that i need a local

Question:practical inorganic chemistry