Glossary - Nn
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Nano- | (n) Prefix used in the SI system meaning "multiply by 10-9". For example 1 nm means "0.000000001 m"; 2.8 ng could also be written "2.8 × 10-9 g". |
| Nanometre | (nm) A unit of length, equal to 10-9 meters, and equal to 10 Å (Angstroms). |
| Native | Naturally occuring forms of precious metals, for example, native copper, native gold, and native silver. Native metals are often very impure. |
| Natural abundance | The average fraction of atoms of a given isotope of an element on Earth. |
| Natural gas | A mixture of methane and other gases, found trapped over petroleum deposits under the earth. |
| Needle valve | A valve which allows fine control over the rate of gas or liquid flowing through it. The valve contains a thin needle with a point that fits into a conical cup. When the valve is closed, the needle blocks an orifice in the bottom of the cup. |
| Net chemical reaction | A reaction that actually occurs as several elementary steps. Equations for net reactions often omit intermediates and catalysts. |
| Net ionic equation | A net ionic equation is an ionic equation with all DEFINE[spectator ions">spectator ions eliminated. For example, Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) = AgCl(s) + Na+(aq) + NO3-(aq) is an ionic equation; the net ionic equation would be Ag+(aq) + Cl-(aq) = AgCl(s) because the sodium and nitrate ions are spectators (they appear on both sides of the ionic equation. |
| Network covalent solid | A substance which consists of an array of atoms held together by an array of covalent bonds. A crystal of a network covalent solid is actually a single, gigantic molecule. Diamond and quartz are examples. |
| Neurotransmitter | Neurotransmitters are molecules that are used to carry signals from one neuron to another. One neuron releases the neurotransmitter near another neuron's receptors. The neurotransmitter diffuses across the gap between the neurons and locks into a receptor site on the surface of the downstream neuron. This induces a change in the downstream neuron. |
| Neutral | 1. having no net electrical charge. Atoms are electrically neutral; ions are not. 2. A solution containing equal concentrations of H+ and OH-. |
| Neutralization reaction | acid-base reaction. A chemical change in which one compound acquires H+ from another. The compound that receives the hydrogen ion is the base; the compound that surrenders it is an acid. |
| Neutrino | An elementary particle produced by certain nuclear decay processes. Neutrinos have no charge and extremely small masses compared to other subatomic particles. |
| Neutron | (n, 10n) An elementary particle found the atomic nucleus of all stable atoms except the hydrogen-1 atom. Neutrons have no charge and have a mass of 1.008665 daltons. |
| Neutron activation analysis | An extremely sensitive technique for analysing trace amounts of elements in a sample. The sample is bombarded with neutrons in a nuclear reactor, making it radioactive. Different elements produce different 'signatures' in the induced radiation which makes determination of their concentration in the sample possible. |
| Newtonian fluid | A fluid whose viscosity doesn't depend on gradients in flow speed. Gases and low-molecular weight liquids are usually Newtonian fluids. |
| Nitrite | (NO2-) 1. The NO2- ion, formed by reaction of nitrous acid with a base. 2. A compound containing the NO2- ion. |
| Nitrate | (NO3-) 1. The NO3- ion, formed by reaction of nitric acid with a base. 2. A compound containing the NO3- ion, for example ammonium nitrate, NH4NO3. |
| Nitric acid | (HNO3) aqua fortis. A corrosive liquid with a sharp odour that acts as a strong acid when dissolved in water. Nitric acid is used to synthesize ammonium nitrate for fertilizers, and is also used in the manufacture of explosives, dyes, and pharmaceuticals. Salts of nitric acid are called nitrates. |
| Nitrogen | (N) Element number 7, a colourless, odourless, tasteless gas that makes up about 80% of the earth's atmosphere. |
| Nomenclature | A system for naming things. For example, "organic nomenclature" is the system used to name organic compounds. |
| Non-Newtonian fluid | Compare with Newtonian fluid. A fluid whose viscosity changes when the gradient in flow speed changes. Colloidal suspensions and polymer solutions like ketchup and starch/water paste are non-Newtonian fluids. |
| Non-particulate | Not composed of distinct particles. |
| Noble gas core | ([X], where X is the symbol of an inert gas element) core configuration. Compare with valence shell. All completely filled shells underneath the valence shell. |
| Node | A point, region, or surface where the amplitude of a standing wave is zero. The probability of finding an electron at an orbital node is zero. |
| Non-electrolyte | A non-electrolyte is a substance which does not ionize in solution. |
| Non-metal | (metal, metalloid) A non-metal is a substance that conducts heat and electricity poorly, is brittle or waxy or gaseous, and cannot be hammered into sheets or drawn into wire. Non-metals gain electrons easily to form anions. About 20% of the known chemical elements are non-metals. |
| Nonpolar | Having a relatively even or symmetrical distribution of charge. |
| Nonpolar molecule | A molecule in which the centre of positive charge and the centre of negative charge coincide. Examples are CCl4 and CO2; counterexamples are CHCl3 and H2O. |
| Normality | (N) normal. A measure of solution concentration, defined as the number of equivalents of solute per litre of solution. |
| Nuclear binding energy | Energy needed to break an atomic nucleus into separate protons and neutrons. |
| Nuclear fission | Splitting of a nucleus into two smaller nuclei and neutrons. The smaller nuclei have higher binding energy than the original nucleus, and fission results in the release of energy. |
| Nuclear fusion | Combination of two smaller nuclei to form a larger nucleus. The larger nucleus has higher binding energy per nucleon than the original nuclei, and fusion results in the release of energy. |
| Nucleation | The process of providing sites for 1) new bubbles to form in a liquid that is boiling or supersaturated with gas; 2) new droplets to condense from a supersaturated vapour, or 3) new crystals to form in a supersaturated solution. Nucleation sites can be scratches in a surface, dust particles, seed crystals, and so on. |
| Nucleic acid | A polymer made of repeating nucleotides. Examples are DNA and RNA. |
| Nucleon | A proton or a neutron in the atomic nucleus. |
| Nucleoside | A nucleotide base bound to a five-carbon sugar. |
| Nucleotide | A molecule which is a basic building block of nucleic acids and which plays a key role in energy transfer in biochemical reactions. Nucleotides consist of a five-carbon sugar, a heterocyclic nitrogen-containing organic base, and a phosphate group. |
| Nucleotide base | A heterocyclic nitrogen-containing base that is a constituent of nucleotides. Examples are adenine, guanine, thymine, uracil, and cytosine. |
| Nuclide symbol | A symbol for an nuclide that contains the mass number as a leading superscript and the atomic number as a leading subscript. For ions, the ionic charge is given as a trailing superscript. For example, the nuclide symbol for the most common form of the chloride ion is 3517Cl-, where 35 is the mass number, 17 is the atomic number, and the charge on the ion is -1. The atomic number is sometimes omitted from nuclide symbols. |
| Nuclide | An atom or ion with a specified mass number and atomic number. For example, uranium-235 and carbon-14 are nuclides. |
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