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Ion
Ion
An atom, or group of atoms, that has gained or lost one or more electrons, developing an electrical charge.
Ions behave differently from electrically neutral atoms and molecules. They can move in an electric field and they can also bind strongly to solvent molecules such as water. Positively charged ions are called cations; negatively charged ions are called anions. Ions carry electrical current through solutions.
Ionic bond
A common type of bond that occurs between two ions when they have opposite charges (cations and anions). For example, when a salty solution is evaporated, sodium cations bond with chloride anions to form common table salt (sodium chloride). Ionic bonds are strong, except in the presence of a solvent.
(See also: Covalent bond and Metallic bond.)
Iridium (Ir)
Element 77 on the periodic table. One of the transition metals. It is a precious (very rare), very dense, silver-white metal. It is obtained as
a by-product of copper and nickel refining. Iridium is so unreactive
it cannot be dissolved by even concentrated acids unless in special combinations. It was discovered
in 1803 by the English chemist Smithson Tennant. The name comes from the Greek word for rainbow because its compounds have a wide variety of colours.
Because it is so hard to obtain and to work, iridium is rarely used on its own. However, it does go into platinum alloys. The alloy is harder and resists chemical attack better than platinum alone. In its alloyed form platinum is usually used for jewellery.
 Iron – Iron and steel have been two of
the most important materials for centuries.
In almost any scene you will find steel.
For example, steel makes the hull, railings,
and chimney of the 19th-century steamboat
in the foreground as well as the hull and superstructure of the tanker in the distance. The bridge deck is also supported by steel cables. The cranes are entirely made from steel. The power station chimneys are also steel. Steel is iron with a small percentage of carbon and many of the other impurities taken out and controlled amounts of others added.
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