Metals and Non-metals

105 elements do not, fortunately, exhibit 105 completely different sets of properties. When the major properties are considered it is seen that the elements fall into two groups, metals or non-metals.There are some distinctions between them. Metals are distinguished from non-metals by their high conductivity for heat and electricity, by metallic lustre and by their resistance to electric current. Their use in industry is explained by the fact that their properties, such as strength and hardness, can be greatly improved by alloying them with other metals. Many elements are classified as semimetals because they have much poorer conductivity than common metals.

Non-metals (carbon, silicon, sulfur) in the solid state are usually brittle materials without metallic lustre and are usually poor conductors of electricity. Non-metals show greater variety of chemical properties than common metals do.Metals can undergo corrosion, changing in this case their chemical and electromechanical properties. In order to protect metals from corrosion the products made of metals and steel are coated by some films.

The contrast between the properties of metals and non-metals is given below. It is not to be expected that all elements in one class will agree in every detail; some differ in one or two properties from the others of their class; these exceptions are indicated in brackets.

MetalsPhysical properties Non-Metals
1. Solid at room temperature (mercury is the only liquid metal). 2. Have a high density (except potassium andsodium). 3. Can be moulded by pressure, i.e. they are malleable. 4. Have high melting points and boiling points. 5. Are good conductors of heat, electricity. 6. Can be drawn into a wire, i.e. they are ductile.	1. Many are liquids and gases at room temperature. 2. Density is usually low. 3. Solid non-metals are brittle. 4. Have low melting points and boiling points. 5. Are poor conductors of heat and electricity (graphite is the only good conductor of electricity among non-metals). 6. Cannot be drawn into a wire.

Chemical properties

7. Have basic oxides. 8. React with dilute acids forming salts. 9. Form positive ions. 10. Are liberated at the cathode during electrolysis (hydrogen during electrolysis acts as a metal).

7. Have acidic oxides. 8. Salts of non-metals are not brittle. 9. Form negative ions. 10. Are liberated at the anode during electrolysis.

The chemical properties are much more conclusive than the physical properties for deciding whether a particular element is to be regarded as a metal or a non-metal, e.g. if an element forms a basic oxide it must be classified as a metal. A basic oxide is never formed by a non-metal.

Unit 16

1. Memorize the following words:

reinforcement remain separate regardless of independent direction applied maintain introduce state stiffness despite level strengthen cavity

усиление, армирование остаться отдельный независимо от независимый направление приложенный поддерживать вводить, внедрять состояние жёсткость несмотря на уровень укреплять полость

посилення, армування залишитися окремий незважаючи на незалежний напрям прикладений піддержувати упроваджувати становище жорсткість незважаючи на рівень зміцнювати порожнина

2. Practise the reading of the following words:

Macroscopic, isotropic, orthotropic, applied, orientation, reinforcement, type, cellulose, fiber, enhance, cavity, resin, ingredients, unavailable, polymerization, design, requirements, raw, performance.

3. Read and translate the text: