Scientific dictionary main page

Scientific dictionary

science park

Table of Elements

Chemical information

Science dictionary

scientific data

site map

Gift Shop

Index (I)








Moment of truth
The word 'nanotechnology' is first coined by University of Tokyo researcher Norio Taniguchi back in 1974.

A   B   C   D   E   F   G   H   I   J   K   L   M  
N   O   P   Q   R   S   T   U   V   W   X   Y   Z  

back (IO-IR) IS - IV next page (IW-IZ)

isoelectronic Chem.
Describing atoms, molecules or ions having the same number of valence electrons and the same structure with similar connectivity of atoms, irrespective of the type of elements involved. For example, the chloride ion (Cl-) and sulfide ion (S2-) are isoelectronic with the argon atom (all have 8 valence electrons). The CO and N2 with 10 valence electrons. The uncharged H2C=C=0 molecule and H2C=N+=N- zwitterion are also isoelectronic.

isomers Chem.
Molecules that contain the same number of constituent atoms (same molecular formula) but have atoms arranged differently (different structural formula). For instance, butane and isobutane (2-methyl propane) are isomers which have the structural formula of CH3-CH2-CH2-CH3 and CH3-CHCH3-CH3.

isomorphs Chem.
Substances of different chemical nature but having the same crystal structure. For example, sodium chloride and magnesium oxide, both crystals have a similar cubic rock-salt structure.

isotonic solution Biol.
A solution with a same osmotic pressure with other solutions. An isotonic solution has equal concentration of solutes with other solutions. When a plant cell or an animal cell is placed in an isotonic solution (for example, 0.85% salt solution), it remains the same size, since there is no osmotic gradient exist between the medium salt solution and that in the cell. The amount of water moving into the cell is equal to the amount of water moving out of the cell.

isothermal process Phys., Chem.
Any process that takes place at constant temperature. Heat can be supplied or removed from the system in such a way so as to maintain a constant temperature.

isotope Phys.
One of a set of atoms which have a same number of protons but different number of neutrons at its nucleus. In other words, isotopes are chemically identical (same atom type) but are differed from one another by their mass. Most elements have more than two isotopes found in nature. For example, tin can have up to 10 naturally occurring isotopes, with a mass number varies from 112 to 124. Very few, such as cesium, only have one natural isotope. However, all elements can produce artificial isotopes (usually radioactive) in the laboratory.

isotope separation Chem.
The separation of the isotopes of an element on the basis of slight differences in their physical properties. An example is the gaseous diffusion of uranium in the form of gaseous hexafluoride compound, in order to separate uranium-235 and uranium-238. Other methods including centrifuging, laser excitations and distillation (as used to separate heavy water).

isotropic number Chem.
The difference between the number of neutrons in an isotope and the number of proton.

back (IO-IR) IS - IV next page (IW-IZ)

A   B   C   D   E   F   G   H   I   J   K   L   M  
N   O   P   Q   R   S   T   U   V   W   X   Y   Z  

| Copyright | Privacy | Disclaimer | Contact |

2004-2010, all rights reserved.