Rare metals

Now read the general information about rare metals and add or correct your answers.

Make the questions to the underlined words.

1. She’s been an analyst for ten years. 2. We ’ve already send our applications. 3. I’ve just called my colleagues. 4. We have already tested all the samples. 5. I’ve never observed such a violent reaction. 6. The liquid has been heated to its boiling point.

11. Warming-up:

1. What are rare metals?

2. Are there many in the Earth?

3. Do rare metals possess the similar properties?

4. What rare metals do you know?

5. Do people use them very seldom as they are so rare?

6. What principle do chemists divide rare metals according to?

About seventy-nine of the one hundred substances are metals. A metal may be defined as a substance which has large conductivity of electricity and of heat, has a characteris­tic luster, called metallic luster, and some other properties.

The metals themselves and their alloys are of great useful­ness to man. Some of them are ductile at higher temperatures and may be easily rolled into sheet. The importance of some alloys is due primarily to their hardness and strength. These properties are a conse­quence of the presence in the metals of very strong bonds be­tween the atoms.

You have probably heard of such metals as germanium, niobium, thorium, etc. They are called rare metals. Some of them are not plentiful in the earth's crust, the other are difficult and rather costly to extract from their ores, that is they are more difficult to work than the common metals.

Rare metals are found not only in the earth’s crust, but also on the ocean bottom, in plants and animals. For example, titanium has been found in animal flesh and bones, cobalt in marine organisms, lithium in plants and so on.

Rare metals, as you will see presently, have different physical and chemical properties, so they naturally fall into sev­eral groups. For instance, lithium, cesium, beryllium are called light rare metals. Molybdenum, rhenium, tantalum, niobium, vanadium, zirconium are referred to as refractory metals.

Rare-earth metals include samarium, cerium, gadolinium, ytterbium, europium, hafnium, etc.

Radium, thorium, uranium, plutonium, californium, po­lonium, etc. are the radioactive elements. While palladium, rhodium and iridium, osmium are the platinum metals.

Finally, the semiconductors are silicon, germanium, se­lenium, bismuth, tellurium, etc.

And now let’s have a closer look at one of the rare mi­raculous metals, which are becoming so important in our age, for these wonder-metals are revolutionizing our life.

Дата добавления: 2014-11-07