Metals and Nonmetals

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1 Till now, scientists have discovered 115* elements. Each of the 115 elements is unique. Each has its own fascinating story. The discovery of the elements started about 8000 years ago, when people obtained shiny materials from the rocks simply by heating. In this way, soft materials, such as copper, silver and gold were discovered. These were followed by lead, tin, iron, mercury, carbon and sulphur. When the Greek philosophers saw ordinary materials going into the foundries at Alexandria, Egypt, and large amounts of gold and silver coming out they assumed that the craftsmen were changing ordinary substances into gold and silver. Thus began the search for the philosophers' stone, a magical substance which could change any base metal into gold or silver. CLASSIFICATION OF ELEMENTS How are elements classified All elements are classified into three categories. Metals Nonmetals Metalloids Metalloids are those elements which behave like both metals and nonmetals. Some common metals, nonmetals and metalloids are listed. Where are the metals, nonmetals and metalloids located in the Periodic Table Metals are placed on the left-hand side, in the middle and at the bottom of the Periodic Table. Nonmetals are placed on the right hand side and in the upper middle part of the Periodic Table. The location of nonmetals is shown by yellow colour. Metalloids are located at the left end of the nonmetals. The location of metalloids is shown by dark yellow colour. The noble gases are present on the extreme right side of the Periodic Table. What are metals Metals are the elements (except hydrogen) which form cations (positive ions) by losing electrons. Thus, metals are electropositive elements. Gold, silver, copper, tin, lead, iron, mercury are typical metals. These metals were known to the ancient people. What are nonmetals The elements which tend to form anions (negative ions) by gaining electrons are termed nonmetals. There are 22 nonmetals. Most nonmetals are gases. Some nonmetals occur as solids. Bromine is the only nonmetal which occurs as liquid under normal conditions. Solid nonmetals Carbon, Sulphur, Phosphorus, Iodine Liquid nonmetal Bromine Gaseous nonmetals Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine What are metalloids The elements which behave like metals as well as nonmetals are called metalloids. Boron (B), Silicon (Si) and Arsenic (As) are metalloids. How is the metallic and nonmetallic character of an element related to its electronic configuration The chemical properties of any element depend upon its electronic configuration. So, whether an element behaves like a metal or nonmetal depends upon its electronic configuration. Thus, a metal and a nonmetal differ in their electronic configurations. Metals generally have 1 to 3 electrons in the outermost shell (or valence shell) of their atoms. Nonmetals usually have 4 to 8 electrons in the outermost shell (or valence shell) of their atoms. Hydrogen and helium, however, do not follow this rule. To illustrate these rules, let us write the electronic configurations of some typical metals and nonmetals. Let us take sodium (Na), magnesium (Mg) and aluminium (Al) as typical metals, and carbon (C), nitrogen (N), oxygen (O), fluorine (F) and neon (Ne) as typical nonmetals. Thus, we see that metals have 1 to 3 electrons, whereas nonmetals have 4 to 8 electrons in their outermost (or valence) shells. Hydrogen (H) and helium (He) are exceptions to this rule. Hydrogen (H) and helium (He) are nonmetals. Hydrogen has only one electron in its outermost (or valence) shell, i.e. hydrogen has only one electron in its K-shell. Helium (He) has two electrons in its outermost (or valence) shell, i.e. helium has two electrons in its K-shell. 1 P a g e

2 What are the general uses of metals Some general uses of metals are described below. > Copper and aluminium are very good conductors of electricity. So, copper and aluminium are used for making electrical wires and cables. Aluminium is also used for making cooking utensils. Aluminium foils are used for packaging of medicines, food materials, etc. Iron is the most widely used metal. Its uses, however, mainly depend upon its carbon content. For example, Cast iron is used for manufacturing wrought iron and steel. It is generally used for making stove burners, gutter pipes, railway sleepers, etc. Steels are used for the manufacture of permanent magnets, engine parts, utensils, surgical equipments, springs, gears, drive shafts, armour plates, etc. Wrought iron is used for making anchors, wire ropes, bolts, chains and agricultural appliances. Zinc is used for the galvanisation of iron. Tin is used for tinning of iron plates/sheets and copper/brass utensils. Thus, zinc and tin are used for protecting iron from rusting. Nickel and chromium are mainly used for electroplating and for the manufacture of stainless steel. Nickel is also used as a catalyst in many industrial processes. Gold and silver are used for making jewellery and for decorative purposes. Sodium, titanium and zirconium are used in atomic energy and space science projects. Zirconium is used for making bullet-proof alloy steels. Mercury is used in thermometers and barometers. Titanium is used in aerospace aircraft frames and engine military hardware marine equipment chemical reactors chemical industries atomic energy and space science projects Titanium, due to its special applications, is considered as a strategic metal, These applications of titanium are due to its high tensile strength lightness resistance to corrosion high melting and boiling points ASSIGNMENT I Classification of elements, Location of metals, nonmetals and metalloids in periodic table, General uses of metals 1. Name the three categories in which all the elements are classified. 2. Identify metals from the following list: Silicon, Carbon, Sulphur, Oxygen, Copper, Mercury, Zinc, Boron, Phosphorus 3. Where are metals located in the Periodic Table? 4. How is the metallic and nonmetallic character of an element related to its electronic configuration? 5. Which of the following is a metal? 6. Mention two uses of aluminium. 7. Name the metal that is used for making bullet-proof steels. 8. Mention two uses of nickel. 9. Why are metals such as titanium, vanadium, chromium, etc. considered strategic metals? COMPARING METALS AND NONMETALS What are the physical properties of metals All metals show some common physical properties. There is however, some variation in each property from metal to metal. Metals are malleable. This means that metals can be hammered into very thin sheets. Gold and silver are among the most malleable metals. Both gold and silver can be hammered into foils much thinner than the thinnest paper. Metals are ductile. This means that metals can be drawn into thin wires. All metals are not equally ductile, i.e. some metals are more ductile whereas others are less ductile. Gold, silver and copper are among the most ductile metals. For example, we can draw a wire of about 200 m length from 100 mg of silver. Metals are good conductors of heat and electricity. Metals permit heat and electricity to pass through them. Silver, copper and aluminium are good conductors of heat and electricity. Silver is the best conductor of electricity. Copper is the next best conductor of electricity. Gold, aluminium and tungsten are good conductors of electricity after silver and copper. Mercury and iron offer greater resistance to the flow of current. Therefore, mercury and iron are not good conductors of electricity. Copper and aluminium are used for making electric wires/cables because they are very good conductors of electricity. Metals are lustrous. This means that metals are shiny. The characteristic shine of metals is called metallic lustre. Metals can be polished. 2 P a g e

3 Metals have high tensile strength. Metals are very strong. They can bear a lot of stress. Most metals except sodium and potassium are hard. Sodium and potassium metals can be easily cut with a knife. Osmium is hard enough to scratch glass. Most metals except sodium and potassium have high melting and boiling points. The melting and boiling points of some common metals are given below. Metal Copper Iron Silver Sodium Potassium Melting point/ C : Boiling point / C : (h) Metals, except sodium and potassium, have high densities. Most metals have high densities. Sodium and potassium have much lower densities. The densities of some common metals are given below: Metal : Copper Iron Silver Gold Sodium Potassium Density, g/ml : Metals are sonorous. Metals when hit by a hammer produce a characteristic metallic sound. All metals except mercury are solids. Under normal conditions, all metals are solids. Mercury is the only metal which is liquid under normal conditions. Metals can form alloys with other metals. Metals can form homogeneous mixtures with other metals. Such solid homogeneous mixtures are called alloys. For example, copper and zinc dissolve in each other to form an alloy called brass. PHYSICAL PROPERTIES OF NONMETALS What are the general physical properties of nonmetals Some common/general physical properties of nonmetals are described below: Nonmetals are brittle. Solid nonmetals break up into pieces when pressed hard or hammered. For example, sulphur and red phosphorus are brittle. Nonmetals are neither ductile nor malleable. Solid nonmetals cannot be drawn into wires, and beaten into leaves / sheets because they are brittle. Nonmetals are insulators. Nonmetals do not conduct heat and electricity. This is because they do not have free electrons. However, graphite is a good conductor of heat and electricity. Nonmetals do not have lustre. Nonmetals are not shiny. However, graphite and iodine are the only nonmetals which have metallic lustre. As a result, nonmetals cannot be polished. Nonmetals usually have low densities and are soft. Diamond (an allotrope of carbon), however, is an exception. Diamond is the hardest natural substance known. Nonmetals have low tensile strength. Solid nonmetals can be easily broken. Nonmetals have low melting and boiling points. However, graphite has a high melting point (3700 C). Sulphur and phosphorus have low melting points white phosphorus melts at 44 C, and sulphur melts at I15 C. Nonmetals are nonsonorous. Nonmetals do not produce sound when hit with an object. Nonmetals may be solid, liquid or gaseous at room temperature. For example, under room temperature conditions, sulphur and phosphorus are solids, bromine is liquid, whereas hydrogen, oxygen and nitrogen are gases. Nonmetals show allotropy. The property of an element to exist in more than one structural form is called allotropy. The different forms of an element are called allotropic forms or allotropes. Some nonmetals can exist in more than one form, i.e. they exist in more than one allotropic form. For example, * Phosphorus exists in five different forms, viz. white or yellow phosphorus, and lamp black are allotropes red phosphorus, violet phosphorus, black phosphorus and scarlet phosphorus. Carbon exists in the following allotropic forms, viz. diamond, graphite, coal, coke, lamp black, etc. Sulphur also exists in various allotropic forms, viz. rhombic sulphur, monoclinic sulphur, plastic sulphur, etc. Home work 2 1. Name a nonmetal which has only one electron in its outermost shell. 2. Which of the following is a nonmetal? 3. Why are nonmetals electronegative in nature? 4. Name a nonmetal which is a good conductor of heat and electricity. 5. Name two nonmetals which are both brittle and nonductile. 6. From the following list, choose metals and nonmetals. State the property on the basis of which you made your choice: Chlorine, Aluminium, Sulphur and Magnesium 7. Name three nonmetals which show allotropy. 3 P a g e

4 8. Name one metal and one nonmetal which are liquid at room temperature? 9. What is meant by the term malleability of a metal? 10. Give two examples of metals which are malleable as well as ductile. 11. Give reason for the following: Metals conduct electricity. CHEMICAL PROPERTIES OF METALS What are the chemical properties of metals Metals are electropositive elements. In chemical reactions, metals lose electrons to form positively-charged ions (called cations). The reactivity of a metal depends upon its nature and the reaction conditions. Some typical chemical reactions of metals are described below. How do metals react with oxygen All metals combine with oxygen to form metal oxides. The reactivity of a metal towards oxygen depends upon its nature. For example, (i) Sodium reacts with oxygen at room temperature to form sodium oxide. (ii) Magnesium does not react with oxygen at room temperature. On heating in oxygen/air, magnesium burns with a dazzling white light to give magnesium oxide. Reaction conditions of metals with oxygen (iii) Zinc reacts with oxygen only on strong heating. Zinc burns with a bluish flame when heated strongly with oxygen. (iv) Iron reacts with oxygen on strong heating without burning. (v) Copper reacts with oxygen slowly only on prolonged strong heating. The reaction conditions for the reactions of sodium, magnesium, zinc, iron and copper with oxygen, it is clear that sodium reacts most readily with oxygen, whereas copper reacts least readily with oxygen. Thus, here sodium is the most reactive metal and copper is the least reactive metal. So, the order of reactivity of these metals with oxygen is Na > Mg > Zn > Fe > Cu most reactive > least reactive reactivity decreases How is a metal oxide formed When a metal reacts with oxygen, it loses its valence electrons to form a positive ion (cation). On the other hand, an atom of oxygen gains two electrons to form oxide (O 2- ) ion. These two oppositely charged ions combine together to form an ionic metal oxide. For example, magnesium (Mg) reacts with oxygen to form magnesium oxide as follows: What is the nature of metal oxides Metal oxides are basic or amphoteric depending upon the nature of metal. The oxides of metals such as sodium, potassium, calcium, magnesium, etc., are basic in nature. The oxides of metals such as aluminium, zinc are amphoteric in nature. Soluble metal oxides react with water to give metal hydroxides (alkalis). The solutions of metal oxides in water turn red litmus blue, and colourless phenolphthalein to pink. For example, sodium oxide (Na20) reacts with water to give sodium hydroxide. Na20 + H > 2NaOH sodium oxide sodium hydroxide (basic oxide) (alkaline in nature) Sodium hydroxide solution, so formed, turns red litmus blue. Red litmus + NaOH -----> Blue litmus 4 P a g e

5 Phenolphthalein+ NaOH Pink colour (colourless) Calcium oxide (CaO) dissolves in water to give Ca(OH)2(aq). Ca(OH)2(aq) is called limewater. It is basic in nature. It also turns red litmus blue. Some metal oxides, e.g., aluminium oxide (A1203), zinc oxide (ZnO) show both acidic as well as basic character. These metal oxides are called amphoteric oxides. For example, How do metals react with water Different metals react with water under different conditions. Some metals react with cold water, whereas some other metals react only with hot water, or steam at red heat. Some metals do not react with steam even at red heat. Reactions of some common metals with water are described in Table. From the results obtained above, we see that sodium reacts with cold water, magnesium reacts with boiling water, aluminium reacts slowly with boiling water, zinc decomposes boiling water slowly but steam rapidly, iron reacts with steam only at red heat, copper does not react even with steam on heating strongly. Thus, we conclude that Magnesium is less reactive than sodium. Aluminium is less reactive than magnesium. Zinc is less reactive than aluminium. Iron is less reactive than zinc. Copper is less reactive than iron. Therefore, the order of reactivity of these metals with water is Na > Mg > Al > Fe > Cu most reactive -> least reactive reactivity decreases How do metals react with dilute acids Usually metals displace hydrogen from dilute acids. The less reactive metals, such as copper, silver, gold, etc. however, do not displace hydrogen from dilute acids. The reactions of metals with dilute hydrochloric acid and dilute sulphuric acid are similar. In both the cases, hydrogen is given out and the corresponding salt is formed. Thus, Metals react with dilute hydrochloric acid to give metal chloride and hydrogen gas. Metals with dilute sulphuric acid give metal sulphate and hydrogen gas. With nitric acid, metals do not produce hydrogen gas. This is because nitric acid is an oxidising acid. The nature of the products formed depends upon the nature of the metal and the concentration of nitric acid.the reactions of some metals with HCI and H2S04 in Table. Thus, we see that the rate at which a metal reacts with a dilute acid depends upon the nature of the metal, i.e. 5 P a g e

6 Sodium Magnesium Zinc Iron Copper (Na) (Mg) (Zn) (Fe) (Cu) Vigorous Rapid Moderate Slow No reaction Therefore, the order of reactivity of these metals with dilute acid is Na > Mg > Zn > Fe > Cu most reactive > least reactive reactivity decreases In other words, we can say that a more electropositive metal displaces hydrogen from a dilute acid more readily. Why do only certain metals displace hydrogen from dilute acids All metals have a tendency to lose electrons. This tendency of losing electrons depends upon the nature of the metal. More electropositive (more reactive) metals lose electrons more easily. A dilute acid (or an acid solution) contains H + ions. So, when a metal which is more electropositive than hydrogen is placed in an acid solution, it loses electrons. These electrons are then gained by H + to produce hydrogen gas. Therefore, the metals which are more electropositive than hydrogen can displace hydrogen from dilute acids. When a metal which is less electropositive than hydrogen is placed in a dilute acid solution it does not lose electrons. As a result, the metals which are less electropositive (less reactive) than hydrogen do not displace hydrogen from dilute acids. Metals, such as copper (Cu), silver (Ag) and mercury (Hg), are less electropositive than hydrogen. So, metals, such as Cu, Ag, and Hg, do not displace hydrogen from dilute acids (or acid solutions). The displacement of hydrogen from dilute acid by a metal more electropositive than hydrogen is illustrated by taking the reaction between zinc and dilute sulphuric acid. When a zinc rod is placed in dilute sulphuric acid, hydrogen gas is liberated. How do metals react with the solutions of other metal salts From the experiments we find that magnesium (Mg), zinc (Zn) and iron (Fe) can displace copper from copper sulphate solution but copper is not able to displace these metals from their salt solutions. All these metals are, therefore, more reactive than copper (Cu). Conclusion. From the results obtained, it can be concluded that a more reactive metal can displace less reactive metals from their salt solutions, but a less reactive metal cannot displace more reactive metals from their salt solutions. ASSIGNMENT 3 1. Which is more metallic sodium or aluminium? 2. Metals are electropositive in nature. Why? 3. Metals behave as reducing agents. Why? 4. Name the metal which burns in air with a golden flame. 5. Name the metal which is stored under kerosene. 6. Name two metals which can displace hydrogen from dilute hydrochloric acid. 7. What types of oxides are formed by metals? Give one example of each. 8. An element reacts with oxygen to form an oxide which dissolves in dilute hydrochloric acid. The oxide formed also turns a solution of red litmus blue. Is the element a metal or a nonmetal? Explain with the help of a suitable example. 9. Name one metal each of the following types. (i) Which react with water at room temperature (ii) Which react with only boiling water 10. What happens when an iron nail is placed in a copper sulphate solution? ACTIVITY SERIES: THE RELATIVE REACTIVITIES OF METALS What is the activity series of metals Some metals are more reactive than others. The tendency of a metal to lose electrons is a measure of its reactivity. Thus, a more electropositive metal is more reactive. The arrangement of metals in a vertical column in the order of decreasing reactivity is called activity series of metals. In the activity series, the most reactive metal is placed at the top, whereas the least reactive metal is placed at the bottom. The activity series is also called reactivity series The more reactive metals have greater tendency to lose electrons. So, more reactive metals are more electropositive or more metallic in nature. Therefore, the electropositive (or metallic) character of metals decreases as we go down from top to the bottom in the activity series of metals. Which metals are more reactive than hydrogen Metals which can lose electrons more readily are more reactive. So, the metals which can lose electrons more readily than hydrogen are more reactive than hydrogen. Therefore, all metals which occur above hydrogen in the activity series are more reactive than hydrogen. The metals which are more reactive than hydrogen are 6 P a g e

7 Potassium (K) Barium (Ba) Calcium (Ca) Sodium (Na) Magnesium (Mg). Aluminium (Al) Zinc (Zn) Iron (Fe) Nickel (Ni) Tin (Sn) Lead (Pb) Which metals are less reactive than hydrogen Metals which can lose electrons less readily than hydrogen are less reactive than hydrogen. Thus, all metals which occur below hydrogen in the reactivity series are less reactive than hydrogen. The metals which are less reactive than hydrogen are Copper (Cu) Mercury (Hg) Silver (Ag) Gold (Au) * Platinum (Pt) What is meant by a metal displacement reaction A reaction in which a more reactive (or more electropositive) metal displaces a less reactive (or less electropositive) metal from its salt solution is called a metal displacement reaction. Some metal displacement reactions are given below. Reaction between zinc metal and copper sulphate solution. Zinc displaces copper from copper sulphate solution. Why do more reactive metals displace less reactive metals from their salt solutions More reactive metals have a strong tendency to lose electrons and get oxidised. So, when a more reactive metal is placed in the solution of a salt of less reactive metal, it loses electrons and gets oxidised.. The electrons so released are picked up by the cation of the less reactive metal present in the solution and get reduced to the metal. Thus, the more reactive metal goes into the solution as cations and the cations of the less reactive metal get reduced to the metal. For example, in the reaction between zinc metal and copper sulphate solution, the reactions are Why do more reactive metals displace less reactive metals from their oxides More reactive metals displace less reactive metals from their oxides on heating. In these reactions, the more reactive metal shows greater affinity for oxygen, and, therefore, gets oxidised to its oxide. The oxide of the less reactive metal gets reduced to the metal. For example, Magnesium displaces copper from copper oxide on heating. Aluminium displaces iron from iron oxide on heating. In these metal displacement reactions, the more reactive metal reduces the oxide of the less reactive metal to the metal. Thus, in these metal displacement reactions, the more reactive metal acts as a reducing agent. Home work 1. Rearrange the following metals in the increasing order of reactivity: aluminium, zinc, mercury and gold. 2. What will you observe when (a) a few zinc pieces are added into the solution of copper sulphate? (b) a few copper pieces are added into the solution of ferrous sulphate? 3. Which of the following reactions is possible? (a) Heating zinc oxide with magnesium or copper (b) Heating copper oxide with zinc or magnesium 7 P a g e

8 HOW DO METALS AND NONMETALS REACT The chemical behaviour of any element depends upon the position of the element in the periodic table. The position of an element in the periodic table is related to its electronic configuration. So, the chemical reactivity of an element depends upon its electronic configuration, i.e. the chemical reactivity of an element depends upon the distribution of electrons in its atom. To understand the reason of the reactivity of an element, let us look into the electronic configurations of some metals, nonmetals with noble gases. The outermost orbit in the case of each noble gas has eight electrons, except in the case of helium which has only two electrons in its outermost orbit. Xenon is the only noble gas which shows limited chemical reactivity by forming fluorides and oxyfluorldes under controlled conditions. Hydrogen atom, however, gains stability by either losing its only electron, or by gaining one to have two electrons (helium structure) in its outermost shell, viz., This rule is illustrated with the help of the following reactions between metals and nonmetals. Reaction between sodium and chlorine: Formation of sodium chloride The electronic configuration of sodium atom (atom no. 11) is 2, 8, 1. So, it has one electron in its valence shell. The electronic configuration of chlorine atom (atomic no. 17) is 2, 8, 7. So, it has 7 valence electrons. When the two combine, there is a transfer of one electron from sodium atom to chlorine atom. During the transfer of an electron, both the atoms attain the noble gas configurations: sodium that of neon (2, 8) and chlorine that of argon (2, 8, 8). The two ions, Na + and Cl~ are then held together by the electronic attraction to form the ionic compound sodium chloride (Na + cl -). We can also show it diagrammatically as follows (only the valence electrons are shown). The coulorrvbic force of attraction between Na + and CI lowers the energy of the system, and hence makes it a stable compound. Reaction between magnesium and chlorine: Formation of magnesium chloride The electronic configurations of magnesium and chlorine are From the electronic configuration given above, we find that All elements having completely filled outermost shell are nonreactive. All elements having less than eight electrons in their outermost shell (except helium which has two electrons in its outermost shell) show a reasonable chemical activity. What is the octet rule Based on these observations, Kossel and Lewis (1916) proposed that "During any chemical reaction, the atoms of all the elements tend to gain stability by acquiring an electronic configuration of the nearest noble gas element." Thus, "during chemical reactions atoms of all elements (except hydrogen) tend to achieve eight electrons in their outermost shell." This is known as the octet rule. Magnesium (atomic no. 12) Chlorine (atomic no. 17) No. of electrons = 12 Electronic configuration: (2, 8, 2) y 8 P a g e No. of electrons = 17 Electronic configuration: (2, 8, 7) Thus, magnesium atom has two electrons in its valence shell and the cl atom has seven valence electrons. Thus, magnesium has two electrons excess of neon configuration (2, 8), and cl is one electron short of argon configuration (2, 8, 8), so one atom of magnesium will transfer its two valence electrons to two chlorine atoms, (one to each) as shown below.

9 IONIC COMPOUNDS AND THEIR PROPERTIES Oxidation is a process which involves loss of electrons. Reduction is a process which Involves gain of electrons. Ionic compounds have high melting points due to strong coulomblc force of attraction between the ions. What are ionic compounds Ionic compounds are also called electrovalent compounds. An ionic (or electrovalent) compound may also be defined as, The compound formed due to the transfer of electrons from the atom of an element to that of another is called an ionic (or electrovalent) compound. Some typical ionic (or electrovalent) compounds are, During the formation of ionic (or electrovalent) compounds, the element whose atom loses electrons is said to be oxidised, and the element whose atom gains electrons is said to be reduced. What are the characteristics of ionic compounds Some important characteristics of ionic (or electrovalent) compounds are described below. Hard, rigid and brittle solids. Ionic (or electrovalent) compounds are hard, rigid and brittle solids. This is due to strong coulombic forces between the oppositely charged ions. High density. Ionic (or electrovalent) compounds have relatively high density. In ionic compounds, the ions are closely packed. This decreases the volume of the system, and as a result density is high. High melting and boiling points. Due to strong coulombic force of attraction, the ions are bound to each other very firmly. As a result, the electrovalent or ionic solids have high melting and boiling points. Solubility. Ionic compounds dissolve easily in polar solvents, such as water, but do no dissolve in nonpolar organic solvents, such as benzene, carbon tetrachloride, etc. Dissociation. When dissolved in solvents like water, or when melted, the ionic compounds dissociate to give free ions. For example, sodium chloride when dissolved in water gives sodium and chloride ions, viz., Conductivity. Solid ionic compounds do not conduct electricity. This is because, in the solid state, the constituent ions are fixed to their positions. The ionic compounds, however, conduct electricity when dissolved in solvents like water or when melted. This is because the ions get free in the solution or in the melt. These free ions move freely in the solution melt, and conduct electricity. Crystalline nature. In ionic compounds, ions are arranged in a regular geometrical fashion. This orderly distribution of ions gives characteristic geometrical shapes to the crystals of electrovalent (or ionic) compounds. OCCURRENCE OF METALS How do metals occur in nature Metals occur in nature in the free as well as in the combined states. The less reactive metals like silver, gold and platinum are generally found in the free state. Most of the metals, however, are found in the combined form as minerals. The less reactive metals like silver, gold and platinum occur in free form gold can be found naturally In because they do not react with air, water, etc. Thus, all metals which are not free form, affected by water and by the gases present in the air occur in free state in nature. On the other hand, all metals which react with water, carbon dioxide, oxygen, and other chemicals which exist in nature, occur in the combined form as compounds. Aluminium (Al) is the most abundant metal in the earth's crust, iron (Fe) and calcium (Ca) being the second and third most abundant metals in the earth's crust. 9 P a g e

10 What are minerals and ores Minerals and ores are defined as follows: Naturally-occurring compounds of metals mixed with earthly materials are called minerals. A mineral may contain a small or large percentage of metal in it. The metal content of a mineral may also vary from place to place. A mineral from which a metal can be extracted on a commercial scale economically and easily is called an ore. Bauxite (A1203-2H20) and Clay (Al203-2Si02-2H20) are the minerals of aluntinium. However, the main ore of aluminium is bauxite (A1203-2H20). Clay cannot be used as an ore of aluminium because it is a silicate mineral. Silicate minerals are not easy to process. How are ores classified Ores are classified on the basis of type of the metal compound present in it. For example, if the metal is present as its oxide in an ore, the ore is called an oxide ore. Some common types of ores are given in Table What is gangue Ores usually contain large quantities of unwanted earthly materials. Such unwanted earthly material present in an ore is called gangue. Gangue may be acidic or basic in nature. What is a flux A substance which during smelting combines with the earthly impurities present in the ore to form a fusible slag is called a flux. There are two types of fluxes. * Acidic flux, e.g. silica (Si02) * Basic flux, e.g. lime (CaO), limestone (CaC03) METALLURGY What is meant by metallurgy The process of extracting pure metals from their ores is called metallurgy. Various steps involved in the extraction of a metal from its ore are Crushing and pulverisation of the ore Concentration (or dressing) of the ore Extraction of metal Refining of metal The actual metallurgical process and the various steps involved in it depend upon nature of the ore and the metal. How is an ore crushed and pulverised Big lumps of the ores are crushed to smaller pieces by hammering it in a hammer mill, and pulverised to a fine powder in pulverisers or stamp mills How is an ore concentrated Ores usually contain unwanted earthly materials called gangue. The gangue must be removed before the ore is processed further. The removal of unwanted earthly materials from an ore is called concentration of ore. Concentration of an ore is also called dressing of ore. Based on the nature of gangue and the ore, the following methods are generally used for the concentration of ores. Hydraulic washing method In this method, the crushed ore is washed with a stream of water. The lighter gangue particles are washed away. The heavier mineral particles settle down to the bottom and can be removed. A typical hydraulic classifier is shown in Fig Magnetic separation method This method is based on difference in the magnetic properties of ore and the gangue. The magnetic separation method is used only when either of the two, ore or gangue, is magnetic. The powdered ore is dropped over a conveyor beltmoving over two rollers, one of which is magnetic. When the ore passes over the magnetic roller, the magnetic and the nonmagnetic materials fall separately Some typical ores which can be concentrated by magnetic separation method Tin stone which contains magnetic impurity wolfram Pyrolusite (a manganese ore) Chromite (a chromium ore) Magnetite (an iron ore) 10 P a g e

11 Froth flotation process Froth flotation process is used for concentrating sulphide ores, particularly of zinc, copper and lead. PRINCIPLE. The froth flotation process is based on the difference in the wetting properties of the ore and gangue particles. The sulphide ore particles are preferentially wetted by pine oil, whereas the gangue particles are wetted by water. PROCESS. The powdered ore is mixed with water and a little pine oil. The mixture is vigorously stirred by passing compressed air. Froth produced rises to the surface and carries the ore particles along with it. The ore particles thus rise to the surface and can be removed easily. The gangue is left behind. Froth flotation method Why are sulphide and carbonate ores roasted or calcined It is easier to obtain metals from their oxide ores than from their sulphide or carbonate ores. Therefore, the sulphide and carbonate ores are converted into oxide by calcination or roasting. These processes are described below. What is meant by calcination of an ore The process of heating an ore strongly in the presence of very limited quantity of air is called calcination. Calcination of an ore is done to convert a carbonate ore into oxide remove moisture /water from the wet/hydrated ores remove volatile impurities from the ore During calcination, the ore becomes porous and dry. For example, calamine (a carbonate ore of zinc) when calcined decomposes to give zinc oxide. What is meant by roasting of an ore Sulphide ores are converted to oxide by roasting. The process of heating an ore (generally, a sulphide ore) strongly below its melting point in the presence of an excess of air is called roasting. Roasting of an ore is done to * convert a sulphide ore to the oxide ore * remove volatile impurities and moisture The chemical reactions during roasting of some common ores are given below. How does calcination differ from roasting Both calcination and roasting involve heating of an ore to obtain oxide of the metal in the ore. The two processes, however, differ from each other in some aspects Calcination During calcination, the ore is heated in the presence of limited quantity of air. Calcination is generally used to convert carbonate ores into oxide ores. Roasting During roasting, the ore is heated in the presence of an excess of air. Roasting is generally used to convert sulphide ores into oxide ores. EXTRACTION OF METALS Metals are extracted from the concentrated ore by a suitable method. The method employed for extracting metal from its ore depends upon the reactivity of the metal. Most reactive Highly reactive metals, e.g. alkali and alkaline earth metals and aluminium are obtained by electrolytic reduction method. Oxides of moderately active metals, e.g. iron, lead, zinc, tin and lead can be reduced by heating with carbon. The oxides of certain transition metals, e.g. manganese dioxide, iron oxide, chromium oxide, etc. can be reduced by heating with aluminium. Metal oxides of less reactive metals, e.g. copper, mercury, lead can be reduced by heat alone. Found in native state (or free metallic state) Chemical reactivity of metals decreases in this direction Least reactive 11 P a g e

12 STEPS INVOLVED IN THE EXTRACTION OF METALS On the basis of reactivity, metals are grouped into the following categories. Metals of very low reactivity. Metals of low reactivity. Metals of medium reactivity. Metals of high reactivity. The reactivity of a metal is indicated by its position in the activity series. The methods employed for the extraction of metals belonging to the various groups are listed. EXTRACTION OF METALS OF VERY LOW REACTIVITY Metals such as platinum, gold and silver show very low reactivity. These metals occur free in nature. So, these metals are obtained by simple physical separation. The heavier metal particles are separated from the sand by hydraulic washing method. Metals like silver and gold are also recovered from the powdered ores by special chemical methods. You will learn about these methods in the higher classes. EXTRACTION OF METALS OF LOW REACTIVITY Metal oxides of less reactive metals, such as mercury (Hg), copper (Cu), lead (Pb) can be reduced by heating alone. That is why, this method is called heat reduction method. When the sulphide ores of less reactive metals like Hg, Cu, Pb, etc. are heated in the air, a part of the ore gets oxidised to oxide. The metal oxide then reacts with the remaining sulphide ore to give the metal and SOz. For example, when cinnabar (HgS) is heated in the air, the following reactions take place. In heat reduction method, roasting and reduction take place simultaneously. EXTRACTION OF METALS AND MODERATE REACTIVITY The metals in the middle of the activity series, such as iron, zinc, lead, copper, etc. are moderately reactive. These usually occur in nature as sulphides or carbonates. It is easier to obtain a metal from their oxides, than from their sulphides and carbonates. Therefore, prior to reduction, the metal sulphides and carbonates are converted into metal oxides. The sulphide ores are converted into oxides by heating strongly in the presence of excess air by a process called roasting. The carbonate ores are converted into oxides by heating strongly in the absence of excess air by a process called calcination. The metal oxide in the calcined/roasted ore can be reduced to the respective metal by using a chemical reducing agent. The choice of reducing agent depends upon the reactivity of the metal. Commonly used reducing agents are carbon, aluminium and magnesium. Reduction with carbon. The oxides of moderately reactive metals, such as iron (Fe), zinc (Zn), copper (Cu), nickel (Ni), tin (Sn) which appear in the middle of the reactivity series can be reduced by heating with carbon (coke), at a higher temperature. The carbon reduction method cannot be used for reducing the oxides of highly reactive (highly electropositive) metals, such as sodium, potassium, calcium, magnesium, aluminium, etc. This is because these metals have greater affinity for oxygen than for carbon. 12 P a g e

13 Reduction with aluminium. Certain metals react with carbon to form compounds. As a result, such metals cannot be obtained by carbon reduction method. Oxides of such metals can be reduced by aluminium powder. For example, aluminium reduces manganese dioxide (Mn02) to manganese (Mn), iron oxide (Fe203) to iron (Fe), and chromium oxide (Cr203) to chromium (Cr). EXTRACTION OF ALUMINIUM BY ELECTROLYTIC REDUCTION OF MOLTEN ALUMINA Aluminium is obtained from alumina (purified bauxite) by electrolytic reduction method. Alumina does not conduct electricity in the solid state. It melts at very high (2348 K) temperature. Therefore, alumina is dissolved in molten cryolite (Na 3 AlF 6 ) containing a small quantity of fluorspar (CaF 2 ). Therefore, a molten mixture of alumina (A ) in cryolite (Na 3 AlF 6 ) and CaF 2 is used as the electrolyte.cryolite (Na 3 AlF 6 ) is added to alumina to lower the melting point of alumina make the electrolyte a good conductor of electricity The molten mixture of alumina, cryolite and fluorspar is then electrolysed in an iron tank lined from inside with carbon-lining. The carbon-lining acts as cathode (-ve electrode). Anode consists of a number of carbon rods suspended from a bus-bar, and dipped into the molten electrolyte. When electric current is passed through the electrolyte, aluminium metal is obtained at the cathode, while oxygen gas is liberated at the anode. During electrolysis, alumina is added to the electrolyte from time to time. This is done to make up for the loss of alumina due to electrolysis. The following reactions take place during the electrolysis of alumina (dissolved in cryolite). Aluminium reduction method is also called alumino-thermic process or thermite process. Such reactions are highly exothermic and the metal so formed is obtained in the molten form. Therefore, this process can be used for welding purposes also. What is thermite welding process (or thermite reaction) A mixture of ferric oxide (Fe203) and aluminium powder (Al) is called thermite. Thermite is placed in a crucible having a plug-hole in its bottom. A ribbon of magnesium, called fuse, is inserted into the mixture. The article to be welded is placed in a fire-clay mould below the plug-hole. When magnesium ribbon fuse is ignited, the following reaction takes place: molten.as a result of heat evolved, iron melts. This white-hot molten iron is tapped from the crucible into the mould. The broken ends of the iron girder (to be welded) actually melt and mix with the molten metal giving a firm and strong weld. EXTRACTION OF METALS OF HIGH REACTIVIT The metals which appear high up in the activity series are highly reactive. These metals cannot be obtained from their compounds by carbon reduction method. This is because these metals have more affinity for oxygen than carbon has. The oxides and halides of the most reactive metals, such as sodium, potassium, magnesium, aluminium, etc. cannot be reduced by reducing agents, such as carbon or aluminium. This is because the cations of highly reactive (highly electropositive) metals are very stable and cannot be reduced by common reducing agents. Such highly electropositive metals are obtained by electrolytic reduction method. In electrolytic reduction method, cation of, the metals is reduce by passing electricity through molten oxide,.hydjoxide,,or, chloride, reduction method is illustrated through,examples. 13 P a g e

14 REFINING OF METALS Metals obtained by reduction processes contain small quantities of various impurities. The process of removing impurities from the metals extracted from their ores is called refining of metals. There are various methods used for refining impure metals. The choice of the method depends upon nature of the metal to be refined. Some common methods used for refining metals are described below. What is the liquation method for refining metals This method is used for refining low-melting metals, such as tin (Sn), lead (Pb), bismuth (Bi), etc. In this method, impure metal is placed on the sloping hearth. The temperature of the sloping hearth is raised slightly above the melting point of the metal. The molten pure metal flows down and the impurities are left behind on the hearth (Fig. 3.9). What is distillation method for refining metals The more volatile metals such as mercury and zinc are purified by distillation method. In this method, the impure metal is heated in a retort. The pure metal distills over and the impurities are left behind. What is electrolytic refining method Most metals, viz. copper, aluminium, chromium, silver, etc. are refined by electrolytic method. In this method, (i) A thick block of impure metal acts as anode. It is connected to the +ve terminal of the battery. (ii) A thin sheet of pure metal acts as cathode. It is connected to the ve terminal of the battery. (iii) An aqueous solution of a suitable salt of the metal is used as the electrolyte. An experimental set-up used for the electrolytic refining of a metal. On passing current through the electrolyte, pure metal gets deposited on the cathode, and the impure metal of the anode dissolves. The impurities either dissolve in the solution or fall below the anode as anode mud. Electrolytic refining of copper and aluminium are described later in this chapter. How does electrolytic reduction differ from carbon reduction Electrolytic reduction : This method is used for the reduction of highly reactive metals. The metals obtained by this method are pure and need no further refining. Carbon reduction This method is used for reducing the oxides of moderately reactive metals. The metals obtained by this method contain some impurities and need to be refined further. Home work 1. What is flux? Give one example. 2. Name one ore of mercury and give its composition. 3. Name (a) an oxide ore of aluminium, (b) an oxide ore of iron. 4. Name the metals extracted from (a) bauxite, (b) haematite. 5. Write a chemical equation showing that aluminium has more affinity than iron for oxygen. (CBSE 1990) 6. Give the chemical compositions of cryolite and bauxite, respectively. (CBSE 1992) 7. Explain why calcium does not occur free in nature. (CBSE 1992 Comptt) 8. The oxide X203 is unaffected by water. Outline a method by which a sample of the metal X can be obtained from its ore. Give one reason as to why you have chosen the method. 9. The circuit shown alongside is meant for electrolytic refining of copper. Redraw the diagram and label it. Mention at which electrode, pure copper will be collected. 10. Why is cryolite added to alumina in the extraction of aluminium? what is an alloy A homogeneous mixture of a metal with other metals or with a nonmetal is called an alloy. Brass is an alloy of two metals copper and zinc. Steel is an alloy mainly of one metal and one nonmetal Iron (metal) and carbon (nonmetal). The properties of alloys are different from those of the constituent metals. For example, The electrical conductivity of an alloy is lower than that of the pure metals. That is why, the conductivity of impure copper is lower than that of pure copper. Alloys usually are harder than the constituent metals. For example, duralumin (an alloy of aluminium, copper, magnesium and manganese), magnalium (an alloy of aluminium and magnesium) are much harder and stronger than aluminium. The presence of small amount of carbon (0.1% to 1.5%) in iron makes it harder and stronger. Alloying is a very good method of improving the properties of a metal. For example, pure iron is soft and can be stretched easily when hot. When it is mixed with a small quantity of carbon, it becomes hard, and strong. Alloying iron with nickel and chromium makes it corrosion-resistant. 14 P a g e

15 The melting point of alloys may be higher or lower than the parent metal. Solder (an alloy of lead and tin) has lower melting point than both the metals. Solder is used for welding electric wires. Alloys are commonly prepared by melting the required component metals in the desired ratio and allowing the molten mass to solidify. ALLOYING OF GOLD Gold is the most malleable and ductile metal. Gold used in making jewellery is usually alloyed with copper and silver. These alloys retain golden colour but are harder than pure gold. The proportion of gold in alloyed-gold is expressed in carats. Pure gold is 24 carats. The alloys commonly used are 9 carats, 18 carats and 22 carats. These alloys contain 9/ 24, 18/ 24,and 22/24 parts as puse gold. EXAMPLE 3.1. Calculate the percentage of pure gold in (a) 22 carats (b) 18 carats gold. SOLUTION. Pure gold is 24 carats. So, (a) Percentage of pure gold in 22 carats gold = 22/24 x 100 = 91.7% (b) Percentage of pure gold in 18 carats gold = 18/24 x 100 = 75.0% CORROSION OF METALS Most of the commonly used metals are strong, ductile and malleable. When in use, these get exposed to the environment. Many of them lose their shine, and get covered with a coloured layer on them. Some even lose their strength and become brittle and weak. This happens due to chemical reactions of the metals with their environment. In common language, this is called corrosion. What is corrosion In our daily life, we see many metals that react with the environment. For example, silver gets tarnished, i.e. it loses its shine, iron gets coated with a brittle brown-coloured layer, copper and brass get a green-coloured deposit on their surfaces, surface of aluminium becomes dull and loses its shine, and so on. Slow destruction of metals due to their interaction with the environment is called corrosion. Corrosion takes place on the exposed surface. When the upper layer of the metal gets corroded, then the inner surface of the metal gets exposed, and the corrosion then continues up to certain depth. Thus for corrosion to take place, the following two conditions are necessary: Presence of oxygen /air Presence of moisture or water vapour Rate of corrosion is affected by the following factors: Electropositive nature of the metal Purity of the metal Presence of reactive gases in the air Presence of electrolytes in water Temperature How can corrosion be prevented Corrosion of metals can be prevented in many ways. Some commonly used methods are described below.. By surface coating. Corrosion of metals can be prevented by coating their surfaces with any of the following materials: By applying oil, grease, paint or varnish on the surface By coating/depositing a thin layer of any other metal which does not corrode. For example, iron surface can be protected from corrosion by depositing a thin layer of zinc, nickel or chromium on it. Copper/brass can be protected by coating it with a thin layer of tin. Tinning of brass utensils is a very common practice in our country. By connecting the metal to a more electropositive metal. A metal can be protected from corrosion by connecting it to a more electropositive metal. As long as the more electropositive metal is there, the given metal does not get corroded. For example, iron can be protected from corrosion by connecting it to zinc or magnesium. RUSTING OF IRON Iron is chemically quite reactive. It is easily attacked by air and water, and gets rusted. Rusting costs a lot to our industrialized society. What is meant by rusting of iron Rusting of iron is the most common type of corrosion. Iron when exposed to moist air (air containing large quantity of water vapour) gets covered with a layer of brown powdery material. The reaction which describes the rusting of iron is Rust is soft, porous and powdery substance. It falls off from the surface of iron, of its own. This exposes the lower layers of iron to the atmosphere. As a result, the rusting continues and over a period of time iron loses its strength. 15 P a g e