I. Read the text. Give the appropriate heading to every part of the text.

1. Precious metals

2. General information about modern state of things

3. Base metals

4. Metals are good conductors

5. Some special uses of metals

6. Noble metals

7. Some historical facts about metals

8. Ferrous metals

9. One of the metal properties is high structural strength

It is known that in ancient times people knew only seven metals. This amount correlated with the number of known planets: the Sun (gold), the Jupiter (tin), the Moon (silver), The Mars (iron), the Mercury (mercury), the Saturn (lead), the Venus (copper). Alchemists thought that these metals appeared in the Earth interior because of the influence of the planet beams. Now people know 108 chemical elements. The majority of them (80) are metals. The most widespread metal in the Earth crust is aluminum, the next after it follows iron, calcium, sodium, potassium and magnesium. The content of the rest metals is insignificant. There are several categories of metals, these are: base metals, ferrous metals, noble metals, precious metals. Given below information gives us the opportunity to know more details about different types of metals.

In chemistry, the term “base metal” is used informally to refer to a metal that oxidizes or corrodes relatively easily, and reacts variably with dilute hydrochloric acid to form hydrogen. Examples include iron, nickel, lead and zinc. Copper is considered a base metal as it oxidizes relatively easily, although it does not react with HCL. It is commonly used in opposition to noble metal.

In alchemy a base metal was a common and inexpensive metal, as opposed to precious metals, mainly gold and silver. A longtime goal of the alchemists was the transmutation of base metals into precious metals. In numismatics, coins used to derive their value primarily from the precious metals content. Most modern currencies are fiat currency, allowing the coins to be made of base metal.

The term “ferrous” is derived from the Latin word meaning “containing iron”. This can include pure iron, such as wrought iron or an alloy such as steel, ferrous metals are often magnetic, but not exclusively.

Noble metals are metals that are resistant to corrosion or oxidation, unlike most base metals. They tend to be precious metals often due to perceived rarity. Examples include tantalum, gold, platinum, and rhodium.

A precious metal is a rare metallic chemical clement of high economic value. Chemically, the precious metals are less reactive than most elements, have high luster and high electrical conductivity. Historically, precious metals were important as currency, but are now regarded mainly as investment and industrial commodities. Gold, silver, platinum and palladium each have an ISO 4217 currency code. The best-known precious metals are gold and silver. While both have industrial uses, they are better known for their uses in art, jewelry, and coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum are the most widely traded. Plutonium and uranium could also be considered precious metals. The demand for precious metals is driven not only by their practical use but also by their role as investments and a store of value. Palladium was of summer 2008 valued at a little, under half the price of gold, and platinum at around twice that of gold. Silver is substantially less expensive than these metals, but is often traditionally considered a precious metal for its role in coinage and jewelry.

Some metals and metal alloys possess high structural strength per unit mass, making them useful materials for earning large loads or resisting impact damage. Metal alloys can be engineered to have high resistance to shear, torque and deformation. However the same metal can also be vulnerable to fatigue damage through repeated use or from sudden stress failure when a load capacity is exceeded. The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many appliances, tools, pipes, non-illuminated signs and railroad tracks.

Metals are good conductors, making them valuable in electrical appliances and for carrying an electric current over a distance with little energy lost. Electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for the most part, are wired with copper wire for its good conducting properties. The thermal conductivity of metal is useful for containers to heat materials over a flame. Metal is also used for heat sinks to protect sensitive equipment from overheating. The high reflectivity of some metals is important in the construction of mirrors, including precision astronomical instruments. This last property can also make metallic jewelry aesthetically appealing.

Some metals have special uses; radioactive metals such as uranium and plutonium are used in nuclear power plants to produce energy via nuclear fission. Mercury is a liquid at room temperature and is used in switches to complete a circuit when it flows over the switch contacts. Shape memory alloy is used for applications such as pipes, fasteners. However they are very good at conducting electricity and heat.