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Index (I)

IA - IC

ID - IF

IG - IJ

IK - IN

IO - IR

IS - IV

IW - IZ

Moment of truth
The Sun, with a diameter of 1,392,000 km, is made of 94% hydrogen atoms.


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I/O address Comp.
Input/Output address. IT is a memory address where the microporcessor communicate with a hardware device. Each device, such as keyboard, mouse, hardware cards, etc, will have a range of unique address located on computer memory. Information will be written or read from the locations in order for the device to carry out an appropriate operation.

ion Chem.
Atom that has lost or gained electron(s) to form a charged particle. These charged particles can interact with one another via electrostatic interactions (Coulombic interactions) and form ionic bond with ions of opposite charge. For example, sodium atom can lose an electron to give sodium ion, Na+. Chlorine atom can gain an electron to give a chloride ion, Cl-. Both ions can interact with each other to give sodium chloride (common salt), a crystalline solid.

ion propulsion Space
A propulsion system for spacecraft by making use of an inert element as fuel such as xenon. Xenon is charged positive as an electric current is applied. The surrounding is also charged positive by applying a voltage so that like-charged repulsions push the xenon out at a very high speed, typically about 126000 km/h. This, in return, pushes the spacecraft forward. It is more efficient when compared with the conventional chemical propulsions in terms of ratio of thrust to propellant used.

The first spacecraft that employed such energy is the Deep Space 1, launched in October 1998 and remained operational until it was retired in December 2001.

ion pump Phys.
Also called a getter pump. It is a type of vacuum pump that reduces the pressure in a container down to about 10-12 torr. Unlike a conventional mechanical pump, ion getter pump does not have moving parts and works by passing a beam of electrons through the residual gas in the container. The gas is ionized and attracted to cathode. The pump works only at very low pressure. Otherwise, the pump will quickly reach its capacity because the absorbed ions eventually saturate the surface of the cathode.

ionic crystal Chem.
A crystal that is made up of ionic species. For example, solid sodium chloride is a crystal consists of sodium ion (Na+) and chloride ions (Cl-) packed in a regular cubic arrangmeent.

ionic radius Chem.
The radius of an ion in a crystalline solid. The assumption is that the ions are spherical with a well-defined size. X-ray diffraction can be used to determine the distance between two ions in a crystal. It is assumed that the distance is the sum of the radii of the two ions. If the ions are the same, the ionic radius is then the half of the interionic distance. Otherwise, the value of the ionic radius is assigned according to the shielding effect of the inner electrons. For instance, the ionic radius of sodium ion (Na+) is 0.096 nm, while the fluoride ion (F-) has a value of 0.135 nm. The sum of the radii is the Na-F ionic distance of 0.231 nm in the crystal of NaF.

In general, anions have larger ionic radii than cations. The larger the negative charge the larger the ion; the large the positive charge the smaller the ion.

ionization energy Chem.
The energy require to remove an electron (usually the one that occupies the outer-most electron orbital) from an atom in the gas state. It is usually describes as the first, second, third etc. ionization energies which refer to the removal of successive number of electrons from the atom. The energy is usually expressed in unit kJ/mol.

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