Langmuir's Theory

the basic idea which was basically correct, that electrons in an atom are arranged in shells which correspond to the periods of the PERIODIC TABLE, and that the most stable configuration (structure) is a complete shell.

Taken from Dictionary of Science

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THE great objection to Langmuir's theory of atomic structure is the difficulty of accepting his hypothesis of stationary electrons.In view of the extraordinary power of the theory, it is important to inquire if Langmuir's argument from the fixity of direction of the valency forces necessarily holds. There appear to be various ways in which the rotation can be imagined of the stable groups of electrons formed by the combination of atoms. The figures represent diagrammatically, according to Langmuir's system, rotating groups of electrons in the outer shells of molecules of neon, fluorine, and oxygen. In the case of the fluorine molecule the six electrons, forming two quartets with two electrons in common, may revolve as a whole. The same thing may happen in the oxygen molecule, or the electrons may revolve as three quartets. Revolution of the stable groups of electrons would add to the stability of the molecules formed by their combination and increase the directional steadiness of the valency forces. In this way it may be possible to reconcile Langmuir's theory with that of Bohr.

Taken from The Smithsonian/NASA Astrophysics Data System

Valency Electrons

the electrons present in the outermost shell of an atom of an element and therefore the ones involved in forming bonds with other atoms when they are shared, lost or gained in the formation of a compound or ION. Some elements always have the same number of valence electrons, e.g., hydrogen has one, ordinary oxygen has two, and calcium has two.

Taken from Dictionary of Science

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In chemistry, valence electrons are the outermost electrons of an atom, which are important in determining how the atom reacts chemically with other atoms. Atoms with a complete shell of valence electrons (corresponding to an electron configuration s²p⁶) tend to be chemically inert. Atoms with one or two valence electrons more than a closed shell are highly reactive because the extra electrons are easily removed to form positive ions. Atoms with one or two valence electrons less than a closed shell are also highly reactive because of a tendency either to gain the missing electrons and form negative ions, or to share electrons and form covalent bonds.

Valence electrons have the ability, like electrons in inner shells, to absorb or release energy in the form of photons. This gain or loss of energy can trigger an electron to move (jump) to another shell or even break free from the atom and its valence shell. When an electron absorbs energy in the form of one or more photons, then it moves to a more outer shell depending on the amount of energy gained. (See also : electrons in an excited state). When an electron loses energy (photons), then it moves to a more inner shell.

Taken from Wikipedia

Valency

is the bonding potential or combining power of an atom or group, measured by the number of hydrogen ions (H⁺, or equivalent) that the atoms could combine with or replace. In an ionic compound, the charge on each ion represents the valency, e.g., in NaCl, both Na⁺ and Cl^- have a valency of one. In covalent compounds, the valency is represented by the number of bonds formed. In carbon dioxide, CO₂, carbon has a valency of 4 and oxygen 2.

The electronic theory of valency explains bonds through the assumption that specific arrangements of outer electrons in atoms (outer shells of eight electrons) give stability (as with the inert gases, which have such a structure) through the transfer or sharing of electrons. Thus with the combination of sodium with chlorine, sodium has one electron in the outer shell, which it loses to chlorine to form the stable structure of the inert gas neon. Similarly, the gain of one electron by chlorine gives it the stable structure of argon.

Taken from Dictionary of Science

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In chemistry, valence, also known as valency or valency number, is a measure of the number of chemical bonds formed by the atoms of a given element. Over the last century, the concept of valence evolved into a range of approaches for describing the chemical bond, including Lewis structures (1916), valence bond theory (1927), molecular orbitals (1928), valence shell electron pair repulsion theory (1958) and all the advanced methods of quantum chemistry.

Taken from Wikipedia

Salt

a compound formed when an ACID reacts with a BASE or when a metal atom replaces one or more hydrogen atoms of an acid. Salts can be formed by other reactions such as two salts reacting together to form different compounds. Salt is also the name given to common salt, or sodium chloride (NaCl), which is found in sea water. It is a vital component of our diet although too much is considered harmful.

Taken from Dictionary of Science

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Salt is a dietary mineral composed primarily of sodium chloride that is essential for animal life, but can be toxic to many land plants. Salt flavor is one of the basic tastes, making salt the oldest, most ubiquitous food seasoning. Salt is also an important preservative.

Salt for human consumption is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodized salt. It is a crystalline solid, white, pale pink or light gray in color, normally obtained from sea water or rock deposits. Edible rock salts may be slightly grayish in color because of mineral content.

Chloride and sodium ions, the two major components of salt, are necessary for the survival of all known living creatures, including humans. Salt is involved in regulating the water content (fluid balance) of the body. Overconsumption of salt increases the risk of health problems, including high blood pressure.

Taken from Wikipedia

Labelled Compound

a compound used in radioactive tracing, where an atom of the compound is replaced by a radioactive ISOTOPE, which can be followed through a biological or physical system by means of the RADIATION it emits.

Taken from Dictionary of Science
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Chemical compound in which a radioactive isotope is substituted for a stable one. The path taken by such a compound through a system can be followed, for example by measuring the radiation emitted.

This powerful and sensitive technique is used in medicine, chemistry, biochemistry, and industry.

Taken from Tiscali