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Home :Glossary

Glossary: G


gamma rays. (gamma-rays) gamma radiation.
A very high energy form of electromagnetic radiation*, typically with wavelengths* of less than 3 pm. Gamma rays are produced by certain nuclear decay processes, and are used to sterilize food.

gas. gases; vapor.
Matter in a form that has low density, is easily compressible and expandable, and expands spontaneously when placed in a larger container. Molecules in a gas move freely and are relatively far apart. "Vapor" often refers to a gas made of a substance that is usually encountered as a liquid or solid; for example, gaseous H2O is called "water vapor".

gel. Compare with colloid*.
A gell is a sol* in which the solid particles fuse or entangle to produce a rigid or semirigid mixture. For example, gelatin dissolved in water produces a sol of protein molecules. When the gelatin is cooked, the protein chains entangle and crosslink, forming a gel which is a mesh of solid protein with trapped pockets of liquid inside. Fruit jellies are also gels

geochemistry. geological chemistry.
The study of materials and chemical reactions in rocks, minerals, magma, seawater, and soil.

geometric isomer.
Geometric isomers are molecules that have the same molecular formula* and bond connections, but distinctly different shapes.

Gibbs free energy. (G) Gibbs' free energy.
A thermodynamic property devised by Josiah Willard Gibbs in 1876 to predict whether a process will occur spontaneously* at constant pressure and temperature. Gibbs free energy G is defined as G = H - TS where H, T and S are the enthalpy*, temperature*, and entropy*. Changes in G correspond to changes in free energy* for processes occuring at constant temperature and pressure; the Gibbs free energy change corresponds to the maximum nonexpansion work that can be obtained under these conditions. The sign of Delta*G is negative for all spontaneous processes and zero for processes at equilibrium*.

Gibbs free energy of formation. (DeltaGf) Gibbs' free energy of formation.
The change in Gibbs free energy* that accompanies the formation of one mole of a compound from its elements in their most stable form.

glutamate receptors.
Glutamate receptors are protein molecules that helps gate the flow of ions across a nerve cell's membrane. They play a role in the formation of new connections between nerve cells (and so, in learning and memory). The receptors are normally activated by aspartate and glutamate. In amnesic shellfish poisoning, domoic acid acts as an excitotoxin* that very strongly activates some of these receptors, preventing their proper functioning.

Ionic salts of glutamic acid* used as flavor enhancers in many foods. Glutamate is usually manufactured by acid hydrolysis of vegetable proteins. Besides being a basic building block of proteins, glutamate functions as a neurotransmitter* that helps neurons grow new connections; as such, glutamate plays an important role in learning and memory. At high concentrations, glutamate can function as an excitotoxin*.

-aminoglutaric%20acid">glutamic acid. Glu; alpha-aminoglutaric acid. Compare with glutamate* and glutamine*.
A naturally occurring amino acid* that has a carboxylic acid* group on its side chain. In proteins, glutamic acid residues can occur with the side-chain carboxylic acid group converted to an amide*; the residue is then called glutamine*.

glutamine. Gln.
The amide* of the amino acid* glutamic acid*. Glutamic acid often occurs as glutamine when built into proteins.

glycerol. (HOCH2CH(OH)CH2OH)
Glycerol is a small molecule with three alcohol groups. It is a basic building block of fats and oils.

glyceride. monoglyceride; diglyceride; triglyceride.
Glycerides are fats and oils that are esters* of glycerol* with one or more fatty acids*. Monoglycerides, diglycerides, and triglycerides contain one, two, and three fatty acids linked to the glycerol, respectively.

glycine. (NH2CH2COOH) Gly; aminoacetic acid.
A naturally occurring aliphatic* amino acid*, found in large quantities in gelatin.

A metric unit of mass, equal to 1/1000 of a kilogram*. Kilograms are the base SI* units for mass, not grams.

An amorphous form of carbon*, made of carbon atoms bound hexagonally in sheets (like chickenwire).

gross error. Compare with systematic error*, random error* and mistake*.
Gross errors are undetected mistakes that cause a measurement to be very much farther from the mean measurement than other measurements.

ground state. Compare with excited state*.
The lowest energy state for an atom or molecule. When an atom is in its ground state, its electrons fill the lowest energy orbitals completely before they begin to occupy higher energy orbitals, and they fill subshells in accordance with Hund's rule* (usually!)

1. A substructure that imparts characteristic chemical behaviors to a molecule, for example, a carboxylic acid* group. (also: functional group*). 2. A vertical column on the periodic table, for example, the halogens*. Elements that belong to the same group usually show chemical similarities, although the element at the top of the group is usually atypical.


General Chemistry Online! Glossary: G

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