The exposure limit for a substance that should (or in the case of OSHA PEL's "shall") not be exceeded. If instantaneous monitoring is not feasible, then a 15-minute time weighted a

A positively charged ion.

1. Chicago Academy of Science 2. Chemical Abstracts Service (which assigns CAS Numbers to chemicals)

The temperature at which the vapor pressure of a liquid is equal to or slightly greater than the atmospheric pressure of the environment. For water at sea level, its boiling point is 100&deg

a charged particle emitted from the nucleus of some atoms as part of those atoms' radioactive decay. Positively charged beta particles are positrons and negatively charged beta particles are

Compounds that when dissolved in water increase the concentration of hydroxide ions (OH). Bases are proton acceptors. Substances with a pH greater than 7 are considered to basic.

A measurement of area equal to E-24 cm2.

The quantum number that distinguishes orbitals of given n having different shapes. This can be any interger value from 0 to n-1.

This is the number of atoms in a 12g sample of carbon-12 (C12). This is equal to 6.0221367E23 atoms. It is named for Italian chemist Amadeo Avogadro (1776-1856) who first stated the principl

The atomic mass of an element divided by its density.

One-half the distance between two adjacent atoms in crystals of elements. This varies according to interatomic forces. 

The number of protons in the nucleus of an atom. This determines an element's structure, properties and location on the periodic table of elements.

A mass unit that is exactly 1/12th the mass of a carbon 12 (C12) atom (approximately 1.67E-24g).

The average mass of all nuclides of an element determined by the proportions in which each nuclide of the element are present within the earth and its atmosphere.

The smallest possible unit of matter that still maintains an element's identity during chemical reactions. Atoms contain one or more protons and neutrons (except hydrogen (H), which normally

Species of subatomic particles that have the same mass and spin as normal particles, however, they have opposite electrical charges from their normal matter counterparts. In the case of anti

A negatively charged ion.

One ten-billionth of a meter (10-10m or 0.0000000001 m) or 1/10th of a nanometer.

Consists of the nucleus of an atom of helium (two protons and two neutrons) and is sometimes emitted from the nucleus of some atoms as part of those atoms' radioactive decay. Alpha particles

A metal in the first column of the periodic table (i.e., lithium, sodium, potassium, rubidium, cesium and francium). With the exception of francium, these metals are all soft and silvery. Th