Chemistry & Environmental Dictionary

Nanometer - Nuclides

Nanometer (nm)

One billionth of a meter (10-9 or 0.000000001 m) or ten Ångstroms.


a particle of matter that has a mass of 1.009 amu but no electrical charge. These particles are constituents of the nucleus of all elements except for hydrogen (H). Neutrons can exist in a free state. Because neutrons have no electrical charge, free neutrons have great penetrating capabilities and are highly damaging to living tissue.

The number of neutrons an element contains can vary (see neutron variability), however, the average number of neutrons any particular element contains can be figured by subtracting the atomic number of an element from it's atomic mass average and rounding to the nearest whole number. When doing this, the resulting number should be noted something similar to: "On average this element contains X neutrons."

NFPA 704

A hazards identification system developed by the National Fire Protection Association (NFPA). This system rates the health, fire and reactivity hazards of a chemical on a scale of 0-4 where zero is no hazard and four is an extreme hazard. In addition this system notes special hazards such as acids, alkalis, corrosives, oxidizers, radioactives or water reactives. This system is commonly used on containers of chemicals or on buildings containing chemicals. Typically it is denoted by the use of a diamond that is divided into four boxes, a blue box for health hazard, a red box for fire hazard, a yellow box for reactivity, and a white box for special hazards.


"Not in my back yard!" The attitude that citizens' have against waste disposal facilities (hazardous or non-hazardous) being built in or near their community, even when it is their own community that generates the waste (hence New York city ships much of their waste to Virginia). This mindset slows down permitting processes for waste facilities of all types regardless of the safety measures employed and results from citizens' basic distrust of waste management companies. Related Article


National Institute for Occupational Safety and Health (United States). NIOSH is responsible for undertaking research and developing recommended health and safety standards.

Noble Gasses inert gasses, rare gasses)

elements belonging to Group 18 of the periodic table. These elements are very unreactive, however, they are not nonreactive as compounds containing these elements have been synthesized. There are no naturally occurring compounds that are made up of these elements.


elements that do not exhibit the characteristics of metals. These elements differ markedly from metals in respect to electronegativity and thermal and electrical conductivity. These elements, in general, are poor conductors and have a high electronegativity. This series includes halogens, noble gasses and some of the metalloids (B, Si, As and Te).


The core of an atom that contains at least one proton and one neutron (except for hydrogen (H), which its most common nuclide doesn't have a neutron). This core is positively charged and contains almost all of an atom's mass.

Nuclides (isotopes)

Forms or species of an element that has the same numbers of protons (hence the same atomic number), but different numbers of neutrons, thus different atomic masses. Technically speaking if an element has only one form that is there is no variability in the number of neutrons that exist in the element, it has no isotopes. There are 21 elements that do not vary in the number of neutrons in their nuclei. More information. While the terms nuclide and isotope are often used interchangeably, there is a subtle difference in useage. Nuclide refers to a specific isotope of an element that has a specific atomic number Z and mass number A. The term isotope can be used to compare 2 different nuclides of the same element. They are isotopes of each other not nuclides of each other, because while they have the same atomic number, they have different atomic masses.

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