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Metals unit 13

1. Learn the notions and their definitions.

Metalloid is a material having prop­erties of both metals and nonmetals.

Resistance he ability to resist chemicals.

Strength the ability to withstand heavy weight without bending, breaking.

Tough not easily cut, broken or worn out.

Conductivity property to pass the electric current..

Magnetism property to attract other metals.

Valency combining capacity.

2. Read the text. Find the difference between metals and metalloids. Translate the text.

Text 1

Metals’ Properties

Metals are any substance that conducts electricity and heat well, is shiny (exhibits what is called metallic luster), is opaque, can be made very strong by proper alloying and other techniques, and can be readily formed by rolling, drawing, and cutting. More than 75% of the elements

are metals. Metals have crystal structure. An atom in a metal is usually closely sur­rounded by a large number of other atoms.

Metalloid is a material having prop­erties of both metals and nonmetals. Most metal­loids have the physical appearance and luster of metals, yet are brittle and are poor conductors of heat and electricity at room temperatures (as are most nonmetallic materials). Included among the metalloid elements are germanium, silicon, arsenic, antimony, boron, and tellurium. In addition, the rare elements astatine and polonium are sometimes considered metalloids.

Thousands of compounds are metalloids.

Metals do not have to be pure elements. Some compounds, such as tantalum carbide, are also metals. Alloys are combinations. For example, copper and zinc, melted together in the proper proportions and solidified, form the alloy brass. Brass is neither a mixture nor a compound but a solution having the same crys­tal structure as the base metal, copper. Alloying usually decreases electrical conductivity.

Metals have a wide range of densities, vary­ing from one-half gram per cubic centimeter (0.5 g/cm3) for lithium to 22.5 g/cm' for os­mium, the densest material known. The melting points of metallic ele­ments vary from -38.0° F (-38.9° C) for mercury to 6170° F (3410° C) for tungsten, while hafnium carbide melts at 8312° F (4600° C).

Metals can be highly reactive (cesium oxidizes and reacts violently with chlorine). They can also be highly resistant to oxidation (gold) or to attack by strong acids (gold, tantalum, stainless steel).

Steel. Carbon steel is the most common as the cheapest and most versatile metal used in industry. It has excellent ductility, permitting many cold-forming operations. Steel is also the most weldable of all commercial metals. It is two-thirds the weight of lead, three times heavier than aluminium.The corrosion resistance of steel depends upon the formation of an oxide surface film. However, resistance to corrosion is somewhat limited. Carbon steel should not be used in contact with dilute acids. Be­tween 90 and 98 per cent, steel can be used up to the boiling point.

Vocabulary

property властивість

withstand витримати

bend гнутися

non-ferrons metals кольорові метали

brass латунь

rusting іржавіючий

substance речовина

conduct проводити

alloy сплав

opaque матовий

draw тягнути

stiffness жорсткість, твердість

toughness міцність, пружність

fracture тріщина

malleability ковкість, тягнучість

ductility пластичність, в’язкість,

тягнучість, ковкість

stainless неіржавіюча, легована

wire провід

copper мідь

foil фольга

solution рішення, розчин

dispersed nodules розсіяні вузлики