9 Record(s)

Acid, acidic

A substance containing hydrogen which, when dissolved in water, produces hydrogen ions such that the Ph is less than 7; any solution containing an acid and with a pH<7. Opposite of Basic.

Alkali, alkaline

Alternate names for base or basic, or having a Ph greater than 7. See also Base.


A unit of measurement in science for small objects; one Angstrom is 10-10 meter, or 100 picometers, or 0.1 nanometers. See our helpful chart on size, weight and concentration at the nanoscale.


A negatively charged ion. Opposite of Cation.


In an electrochemical cell, the electrode at which oxidation occurs (the loss of an electron). Opposite of Cathode.


An atom is one of the basic units of matter. Atoms form the building blocks of the simplest substances called chemical elements. Atoms vary greatly in weight, but they are all about the same size, ranging from 0.3 to 3 angstroms. For example, an atom of plutonium, one of the heaviest elements, weighs more than 200 times as much as an atom of hydrogen, the lightest element. Yet the diameter of a plutonium atom is about 151 picometers, only about three times that of a hydrogen atom, which is about 53 picometers.

Atomic Absorption Spectrometry (using flame Atomic Absorption Spectrometer)

A technique of analytical chemistry where a solution containing a metal ion and/or suspension is aspirated into a high temperature flame. The resulting atoms absorb light emitted from a lamp of a wavelength specific for each metal. The amount of light absorbed is a quantitative measure of the concentration of metal in the solution. See also Mass Spectrometry.

Atomic Cluster (Atomic Quantum Cluster)

This term is used for sub-nanometer (< 1nm) or pico-scale sized substances or structures. In chemistry, a cluster is an ensemble or group of bound atoms intermediate in size between a molecule and a bulk solid where elements vary in the expression of their intensive properties. Transition metals, such as silver, form especially robust clusters. The term cluster was coined by F.A. Cotton in the early 1960s to refer to compounds containing metal-to-metal bonds. In another definition, a cluster compound contains a group of two or more metal atoms where direct and substantial metal-to-metal bonding is present. The prefix 'nuclear' is used to identify elemental combinations, for example 'heteronuclear' means there are two different elements and 'polynuclear' would mean there are three or more different elements within the cluster. Since intensive properties can change as size decreases, pico-scale silver clusters initiate quantum effects and become exponentially efficient as catalysts and as sources of silver ions (Ag+) for reactions.

Agency for Toxic Substances and Disease Registry (ATSDR)

A federal public health agency of the U.S. Department of Health and Human Services which serves the public by analyzing research and taking responsive public health actions, providing trusted health information to prevent harmful exposures and diseases related to toxic substances.