Page 10 - Curriculum Visions Dynamic Book

(Above) A magnetized piece of iron is a magnet. Its magnetic field is shown here, marked out in iron filings.
(Below) The reactivity series of metals.
Metals that produce a large amount of magnetism when a current passes through
them are called ferromagnetic metals. Ferro is a word for iron, the most common of these special metals and the one in which the
property was first discovered. Ferromagnetic metals can be taken from
the soil and will remain magnetic, although not forever. The softer the material, the faster
the magnetism weakens. Most so-called permanent magnets are given a long life by
magnetizing a hard metal such as steel (strictly speaking, steel is not a pure metal but has carbon
and other elements in it). In this case the loss of magnetism is very slow. That does not mean soft materials have no use. On the contrary, it is often
important to have materials that do not keep their magnetism. That is one reason soft iron is used inside electrical transformers.
Whether it is a hard or a soft material, if you heat any metal, the magnetism is gradually lost.
The reactivity of metals
Because metals make up so many of the elements, you can expect some metals to be much more reactive than others.
The least reactive metal is gold. No matter how long you leave it in the air, for example, it will not combine with the oxygen in the air and develop a tarnish. Instead, it remains bright forever. It is this property that attracted ancient civilisations to it and still attracts us today.
Most metals do react with oxygen, causing the surface to become covered in an oxide coating so
thin as to be invisible. Once this coat has formed, most metals will stop reacting. Only the most reactive metals, such as sodium, will continue to react in air.
Metal oxide coatings provide very good protection from reactions at room temperatures in dry air. However, they become less effective at high
Element
Potassium (K)
Sodium (Na)
Calcium (Ca)
Magnesium (Mg)
Aluminium (Al)
Manganese Mn)
Chromium (Cr)
Zinc (Zn)
Iron (Fe)
Cadmium (Cd)
Tin (Sn)
Lead (Pb)
Hydrogen (H2)
Copper (Cu)
Mercury (Hg)
Silver (Ag)
Platinum (Pt)
Gold (Au)
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