Glossary of chemical terms

nautical mile
	Nautical mile is a legal international unit of length temporarily maintained with the SI. It is still used in navigation (mercantile marine, aviation). It is equal to the length of an arc of one minute measured at a latitude of N45° (mile = 1852 m). The international nautical mile has been taken equal to the nautical mile.
Néel temperature
	Néel temperature (TN) is the critical temperature above which an antiferromagnetic substance becomes paramagnetic. The phenomenon was discovered around 1930 by L.E.F. Néel (1904- ).
neoprene
	Neoprene is a synthetic ruber made by polimerizing the compound 2-chlorobuta-1,2-diene. Neoprene is often used in place of natural rubber in applications requiring resistance to chemical attack.
Nessler's reagent
	Nessler's reagent is a solution of mercury(II) iodide (HgI2) in potassium iodide and potassium hydroxide named after Julius Nessler (1827-1905). It is used in testing for ammonia, with which it forms a brown coloration or precipitate.
neutralization
	Neutralization is the process in which an acid reacts with a base to form a salt and water. H+ + OH- H2O
neutrino
	Neutrino is a stable elementary particle in the lepton family. Neutrinos have zero (or at least near-zero) rest mass and spin 1/2.
neutron
	Neutron is an elementary particle on spin 1/2 and zero charge. The free neutron has a mean lifetime of 887 seconds. Neutrons and protons, which are collectively called nucleons, are the constituents of the nucleus.
neutron number
	Neutron number (N) is a characteristic property of a specific isotope of an element, equal to the number of neutrons in the nucleus.
newton
	Newton (N) is the SI unit of force, being the force required to give a mass of one kilogram an acceleration of 1 m s-2 (N = kg m s-2). It is named after British scientist Sir Isaac Newton (1642-1727).
NMR
	See Nuclear magnetic resonance
noble gas
	Noble gas refers to any element of the group of six elements in group 18 of the periodic table. They are helium (He), neon (Ne), argon (Ar), krypton (Kr) , xenon (Xe), and radon (Rn). Unlike most elements, the noble gases are monoatomic. The atoms have stable configurations of electrons. Therefore, under normal conditions they do not form compounds with other elements. They were generally called inert gases until about 1962 when xenon tetrafluoride, XeF4, was produced in the laboratory. This was the first report of a stable compound of a noble gas with another single element.
non-metals
	Non-metals are defined as elements that are not metals. Their physical properties generally include: - They are poor conductors. - They are brittle, not ductile in their solid state. - They show no metallic luster. - They may be transparent or translucent. - They have low density. - They form molecules which consists of atoms covalently bonded; the noble gases are monoatomic. Their chemical properties are generally: - They usually have four to eight valence electrons. - They have high electron affinities (except the noble gases) - They are good oxidizing agents (except the noble gases) - They have hydroxides which are acidic (except the noble gases) - They are electronegative.
nuclear magnetic resonance
	Nuclear magnetic resonance (NMR) is a type of radio-frequency spectroscopy based on the magnetic field generated by the spinning of electrically charged atomic nuclei. This nuclear magnetic field is caused to interact with a very large (1 T - 5 T) magnetic field of the instrument magnet. NMR techniques have been applied to studies of electron densities and chemical bonding and has become a fundamental research tool for structure determinations in organic chemistry.
nuclear reactor
	Nuclear reactor is an assembly of fissionable material (uranium-235 or plutonium-239) designed to produce a sustained and controllable chain reaction for the generation of electric power. The essential components of a nuclear reactor are: 1. The core, metal rods containing enough fissionable material to maintain a chain reaction at the necessary power level (as much as 50 t of uranium may be required). 2. A source of neutrons to initiate the reaction (such as a mixture of polonium and beryllium) 3. A moderator to reduce the energy of fast neutrons for more efficient fission (material such as graphite, beryllium, heavy water, and light water are used) 4. A coolant to remove the fission-generated heat (water, sodium, helium, and nitrogen may be used) 5. A control system such as rods of boron or cadmium that have high capture cross sections (to absorbs neutrons) 6. Adequate shielding, remote-control equipment, and appropriate instrumentation are essential for personnel safety and efficient operation.
nucleic acids
	Nucleic acids are macromolecules (relative molecular mass over 5 000 000), the major organic matter of the nuclei of biological cells, made up of nucleotide units, and hydrolyzable into certain pyrimidine or purine bases (usually adenine, cytosine, guanine, thymine, uracil), D-ribose or 2-deoxy-D-ribose.
nucleon
	Nucleon is a collective term for the proton and neutron.
nuclide
	Nuclide is a species of atoms in which each atom has identical atomic number Z and identical mass number A.

 

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