Weak Pull HCl Strong Pull

+ PERIODIC– CLASSIFICATION 8 H Cl OF ELEMENTS Elctronon TrTfansferredd

Learning Objectives

After a thorough perusal of this unit, the students will be able to: ‹ recognize the basis of the modern periodic law and its development. ‹ list the features of groups and periods of the modern periodic table. ‹ explain the trend in periodic properties along the periods and groups. ‹ distinguish between ores and minerals . ‹ list out the types of separation of impurities from the ores. ‹ recall the various places of occurrences of minerals in the state of Tamil Nadu. ‹ put forth the properties of metals. ‹ identify the stages involved in metallurgical processes. ‹ think scientifically on alloys and their types. ‹ develop an idea on amalgam. ‹ understand the reason for corrosion and the methods of its prevention.

periods in such a way that each group contained INTRODUCTION a certain number of elements (like an array of The eighteenth and nineteenth centuries fruits and vegetables showing orderliness) witnessed a rapid development in chemistry with similar properties and periods showing a in all spheres of scientific activities. By 1860, regular gradation. So, scientists made several scientists had already discovered 60 elements attempts to arrange elements in a logical way. and determined their atomic masses. They You have studied about all these early attempts noticed that some elements had similar of arrangement of elements in standard IX. In properties and hence arranged them into continuation of the knowledge gained in the groups. During this period, several new topic periodic classification of elementsin elements were discovered. These elements standard IX with earlier concepts and their were found to have different properties. It was subsequent deliberations, you get set to go realized that instead of studying the properties ahead with the higher order of thinking to of all these elements individually, it would be enhance your knowledge on the properties of more convenient to divide them into groups and elements.

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10th_Science_Unit-8.indd 106 21-02-2019 18:38:56 Figure 8.1 shows the modern periodic table of 8.1 MODERN PERIODIC LAW 118 elements discovered so far. Mendeleev’s periodic table had some As you have studied the features of the discrepancies, which were difficult to overcome. modern periodic table in standard IX, here For example, the atomic mass of argon (39.95 let us confine to the study of the features of amu) is greater than that of potassium (39.10 periods and groups. amu), but argon comes before potassium in the periodic table. If elements were arranged 8.2.1 Features of Periods solely according to increasing atomic mass, argon would appear in the position occupied ‹ The horizontal rows are called periods. by potassium in our modern periodic table (see There are seven periods in the periodic in Figure 8.1). No chemist would place argon, a table. gas with no tendency to react, in the same group ‹ First period (Atomic number 1 and 2): as lithium and sodium,which are two highly This is the shortest period. It contains reactive metals. This kind of discrepancies only two elements (Hydrogen and suggested that some fundamental property Helium). other than atomic mass must be the basis of ‹ Second period (Atomic number 3 to 10): periodicity. The fundamental property turned This is a short period. It contains eight out to be the number of protons in an atom’s elements (Lithium to Neon). nucleus, something that could not have been ‹ known by Mendeleev and his contemporaries. Third period (Atomic number 11 to 18): This is also a short period. It contains Henry Moseley, a British scientist in 1912, eight elements (Sodium to Argon). discovered a new property of elements called ‹ atomic number, which provided a better basis Fourth period (Atomic number 19 to 36): for the periodic arrangement of the elements. This is a long period. It contains eighteen It is a well-known fact that atomic number of elements (Potassium to Krypton). This an element is equal to the number of protons includes 8 normal elements and 10 or the number of electrons present in the transition elements. neutral atom of an element. The periodic law ‹ Fifth period (Atomic number 37 to 54): was, therefore, modified to frame a modern This is also a long period. It contains periodic law, which states that 18 elements (Rubidium to Xenon). This “The physical and chemical properties includes 8 normal elements and 10 of the elements are the periodic functions of transition elements. their atomic numbers”. ‹ Sixth period (Atomic number 55 to 86): This is the longest period. It contains 32 elements (Caesium to Radon). This 8.2 MODERN PERIODIC TABLE includes 8 normal elements, 10 transition With reference to the modern periodic law, elements and 14 inner transition elements the elements were arranged in the increasing (Lanthanides). order of their atomic numbers to form the ‹ Seventh period (Atomic number 87 modern periodic table. The modern periodic to 118): Like the sixth period, this table is a tabular arrangement of elements in period also accommodates 32 elements. rows and columns, highlighting the regular Recently 4 elements have been included repetition of properties of the elements. by IUPAC.

107 Periodic Classificaiton of Elements

10th_Science_Unit-8.indd 107 21-02-2019 18:38:56 Modern Periodic Table Periodic Modern

Figure 8.1 Figure

10th Standard Science 108

10th_Science_Unit-8.indd 108 21-02-2019 18:38:59 8.2.2 Features of Groups 8.3 PERIODIC TRENDS IN ‹ The vertical columns in the periodic table PROPERTIES starting from top to bottom are called The electronic groups. There are18 groups in the periodic configurations of elements table. help us to explain the ‹ Based on the common characteristics periodic recurrence of of elements in each group, they can be physical and chemical grouped as various families. properties. Anything which repeats itself after a regular Group Number Family interval is called periodic and this behaviour 1 Alkali Metals is called periodicity. Some of the atomic 2 Alkaline earth metals properties of the elements are periodic. 3 to 12 Transition metals Properties such as atomic radius, ionic 13 Boron Family radius, ionisation energy, electronegativity, electron affinity, show a regular periodicity 14 Carbon Family and hence they are called periodic properties. 15 Nitrogen Family The main significance of the modern periodic 16 Oxygen Family (or) table is that it gives a clear understanding of the Chalcogen family general properties and trends within a group or 17 Halogens a period to predict with considerable accuracy, the properties of any element, even though that 18 Noble gases element may be unfamiliar to us. Let us discuss the periodic trend of some of the properties. ‹ The Lanthanides and Actinides, which form part of Group 3 are called inner 8.3.1 Atomic Radius transition elements. ‹ Except 'group 0', all the elements present Atomic radius of an atom is defined as in each group have the same number of the distance between the centre of its nucleus electrons in their valence shell and thus and the outermost shell containing the valence have the same valency. For example, all electron. Direct measurement of the radius of the elements of group 1 have one electron an isolated atom is not possible. Except for in their valence shells (1s1). So, the noble gases, usually the atomic radius is valency of all the alkali metals is ‘1’. referred to as covalent radius or metallic radius depending on ‹ As the elements present in a group the nature of the have identical valence shell electronic bonding between the configurations, they possess similar concerned atoms. chemical properties. Atomic radius in metal ‹ (a) The physical properties of the elements atoms is known as in a group such as melting point, boiling metallic radius. It is point and density vary gradually. defined as half the (b) ‹ The atoms of the 'group 0' elements have distance between the Figure 8.2 stable electronic configuration in their nuclei of adjacent (a) Metallic Radius valence shells and hence they are unreactive. metal atoms (Figure 8.2 (b) Covalent Radius

109 Periodic Classificaiton of Elements

10th_Science_Unit-8.indd 109 21-02-2019 18:38:59 (a)). In non-metallic elements, their atomic Li Li+ FF– radius is known as Covalent radius. It is defi ned as half the distance between the nuclei of two covalently bonded atoms of the 156 90 69 119 same element in a molecule (Figure 8.2 (b)). Na Na+ Cl Cl– For example, let us consider H2 molecule. Th e distance between the two hydrogen nuclei of the molecule is 0.74 Å. So its covalent radius is 0.74/2 = 0.37 Å. 186 11691 167 Atomic radius of Hydrogen When you look at the Radii in Picometers variation of the atomic Figure 8.5 HH Relative ionic radii of cation radii in the periodic table, and anion there are two distinct Figure 8.3 trends. Along the period, Atomic radius the ion. You know that ions are formed when from left to right, the an atom lose or gain electrons. When a neutral atomic radius of the elements decreases whereas atom loses an electron, it becomes a positively along the groups, from the top to bottom, the charged ion called cation, whereas the gain of atomic radius increases. Th e increase, down a an electron by a neutral atom forms a negatively group, is due to the increase in the valence shell charged ion called anion. Th e size of the ions number down the group. As the shell number is important to determine their behaviours increases, the distance between the valence shell in solutions and the structure of ionic solids. and the nucleus increases. In contrast, when Th e size of a cation is always smaller than its you observe along the period, the shell number corresponding neutral atom. But, the anion is remains the same but the number of protons larger than its neutral atom. (i.e. atomic number) increases. More and more For instance, lithium and sodium lose the positive charges impose a strong attraction single electron from their outermost energy level over the electrons and thus the electron cloud to form cations. Th e ions so formed are smaller shrinks towards the nucleus, which results in because the remaining electrons are at a inner the decrease in the atomic size. Figure 8.4 shows cells and attracted more strongly by the nucleus. how the atomic radius decreases from lithium Fluorine and chlorine become negative ions by to boron. gaining an electron. When electrons are added, the charge on the nucleus is not great enough to hold the increased number of electrons as closely as it holds the electrons in the neutral atom. So, as seen in atomic radius, ionic radii also decrease along the period from left to right and increase down the group.

Figure 8.4 Variation of atomic radius 8.3.3 Ionisation Energy Ionisation energy is the minimum 8.3.2 Ionic Radii energy required to remove an electron from It is defi ned as the distance from the centre a gaseous atom in its ground state to form of the nucleus of the ion upto the point where a cation. It is otherwise called ionisation it exerts its infl uence on the electron cloud of enthalpy. It is measured in kJ/mol. Higher

10th Standard Science 110

10th_Science_Unit-8.indd 110 21-02-2019 18:39:00 the ionisation energy, it is more difficult to and hence it pulls the shared electrons towards remove the electron. itself more strongly than hydrogen. Thus, when As the atomic size decreases from left the bond breaks, the bonding electrons are left + – to right in a period, more energy is required with chlorine forming H and Cl ions. It is to remove the electrons. So, the ionisation represented, diagrammatically, as shown below: energy increases along the period. But, down

the group, the atomic size increases and hence Weak Pull HCl Strong Pull the valence electrons are loosely bound. They require relatively less energy for the removal. Thus, ionisation energy decreases down the group in the periodic table. + –

Note: As the positive charge increases the size H Cl of the cation decreases As the negative charge increases the Elctron Transferred size of the anion increases Figure 8.6 Relative electronegativity of 8.3.4 Electron Affinity H and Cl

Electron affinity is the amount of energy Electronegativity is based on various released when a gaseous atom gains an electron experimental data such as bond energy, to form its anion. It is also measured in kJ/mol ionization potential, electron affinity, etc. and represented by the following equation: Pauling scale is the widely used scale to A + e– → A– + Energy (g) (g) determine the electronegativity, which in Cl + e– → Cl– + energy (g) (g) turn predicts the nature of bonding (ionic or Like ionisation energy, electron affinity covalent) between the atoms in a molecule. also increases from left to right in a period and Electronegativity of some of the elements decreases from top to bottom in a group. are given below F = 4.0, Cl = 3.0, Br = 2.8, I = 2.5, H = 2.1, Na = 1 More to Know If the difference in electronegativity Noble gases show no tendency to accept between two elements is 1.7, the bond electrons because the outer s and p orbitals has 50% ionic character and 50% covalent of noble gases are completely filled. No more character. electrons can be added to them and hence If the difference is less than 1.7, the bond their electron affinities are zero. is considered to be covalent. If the difference is greater than 1.7, the 8.3.5 Electronegativity bond is considered to be ionic. Electronegativity of an element is the Along the period, from left to right in the measure of the tendency of its atom to attract the periodic table, the electronegativity increases shared pair of electrons towards itself in a covalent because of the increase in the nuclear charge bond. Let us consider HCl molecule. Both the which in turn attracts the electrons more strongly. hydrogen and chlorine atoms share one electron On moving down a group, the electronegativity each to form the covalent bond between them. of the elements decreases because of the chlorine atom has a higher electronegativity increased number of energy levels.

111 Periodic Classificaiton of Elements

10th_Science_Unit-8.indd 111 21-02-2019 18:39:00 Periodic (iii) Refining of the metal: It is the process of In Periods In Groups Property purification of the metal. Atomic radius Decreases Increases 8.4.1 Terminology in metallurgy Ionic radius Decreases Increases Minerals: A mineral may be a single compound or a complex mixture of various Ionisation energy Increases Decreases compounds of metals found in the Earth. Electron affinity Increases Decreases Ore: The mineral from which a metal can Electronegativity Increases Decreases be readily and economically extracted on a large scale is said to be an ore. Test yourself All ores are Predict the nature of the bond in the minerals; But following molecules. all minerals are not ores. (i) NaCl (ii) NaBr (iii) NaI s Why? Conceptual (iv) NaF (v) NaH Thought

For example: Clay (Al2O3. 2 SiO2. 2 H2O)

and bauxite (Al2O3.2 H2O) are the two minerals 8.4 METALLURGY of aluminium, but aluminium can be profitably Human life is associated with various extracted only from bauxite. Hence, bauxite is metals. We use metals in our day to day an ore of aluminium and clay is its mineral. activities. It is the utmost need to have some Mining: The process of extracting the ores metals like sodium, potassium, calcium, iron, from the Earth's crust is called mining. etc. in the human body. Deficiency of these Gangue or Matrix: The rocky impurity metals affects the metabolic activities thereby associated with an ore is called gangue or matrix. causing diseases. So, metals Flux: It is the substance added to the play a vital role in our life. ore to reduce the fusion temperature and to In this section, let us discuss remove the impurities. E.g. Calcium oxide how metals are obtained (basic), Silica (acidic). If the gangue is acidic, from various sources by the then basic flux is added and vice versa. process of metallurgy. Slag: It is the fusible product formed Metallurgy is a science of extracting when a flux reacts with a gangue during the metals from their ores and modifying the extraction of metals. metals into alloys for various uses, based on Flux + Gangue → Slag their physical and chemical properties and Smelting: Smelting is the process of their structural arrangement of atoms. A reducing the roasted metallic oxide from the metallurgical process involve three main steps metal in its molten condition. In this process, as follows: impurities are removed as slag by the addition (i) Concentration or Separation of the ore: of flux. It is the process of removal of impuries 8.4.2 Types of separation or from the ore. concentration of an ore (ii) Production of the metal: It is the There are four major types of separation convertion of the ore into metal. of ores based on the nature of the ore. The

10th Standard Science 112

10th_Science_Unit-8.indd 112 21-02-2019 18:39:00 different kinds of ores of metals are given in metal wheels, one of which is magnetic. The Table 8.1 magnetic particles are attracted to the magnetic Concentration of the crushed ore is done wheel and fall separately apart from the non- mainly by the following methods: - magnetic particles. (i) Hydraulic (Gravity Separation) (iii) Froth floatation method Principle: This process depends on Principle: The difference in the densities the preferential wettability of the ore with or specific gravities of the ore and the gangue oil (pine oil) and the gangue particles by is the main principle behind this method. water. Lighter ores, such as sulphide ores, Oxide ores are purified by this method. e.g., are concentrated by this method. e.g., Zinc blende (ZnS). Haematite Fe2O3 the ore of iron. Method: The ore is poured over a sloping, Froth bubbles Compressed vibrating corrugated table with grooves and a jet carrying sulphide air ore particals of water is allowed to flow over it. The denser ore particles settle down in the grooves and lighter

gangue particles are washed down by water. Sulphide ore particals (ii) Magnetic separation method Water Principle: The magnetic properties of containing pine oil the ores form the basis of separation. When either the ore or the gangue is magnetic, this Gangue

method is employed. e.g., Tinstone SnO2, the Froth floatation process for the concentration ore of tin. of sulphide ores. Finely ground ore Figure 8.9 Froth floatation

Method: The crushed ore is taken in a large tank containing oil and water and agitated with a current of compressed air.The

Magnetic roller ore is wetted by the oil and gets separated from the gangue in the form of froth. Since the ore

Magnetic is lighter, it comes on the surface with the froth particles and the impurities are left behind. e.g., Zinc Non-Magnetic blende (ZnS). particles (iv) Chemical method or Leaching Figure 8.8 Magnetic separation This method is employed when the ore is Method: The crushed ore is placed over in a very pure form. a conveyer belt which rotates around two

Table 8.1 Types of ores

Oxide Ores Carbonate Ores Halide Ores Sulphide Ores . Bauxite (Al2O3 2H2O) Marble (CaCO3) Cryolite(Na3AlF6) Galena (PbS)

Cuprite(Cu2O) Magnesite ((MgCO3) Fluorspar(CaF2) Iron pyrite (FeS2)

Haematite ( Fe2O3) Siderite(FeCO3) Rock salt (NaCl) Zinc blende (ZnS)

113 Periodic Classificaiton of Elements

10th_Science_Unit-8.indd 113 21-02-2019 18:39:02 More to Know

Extraction of metal from metal oxide can be categorized into three types. More reactive metals Medium reactive metals Less reactive metals Na,K,Ca,Mg,Al Zn,Fe,Pb,Cu Ag,Hg Electrolytic reduction of Chemical reduction of metal Thermal decomposition of metal oxide into metal oxide into metal using coke metal oxide into metal

The ore is treated with a suitable reagent boiling points and vaporize only at high such that the ore is soluble in it but the temperatures (exceptions: gallium, mercury, impurities are not. The impurities are removed sodium and potassium). by filtration. The solution of the ore, ie., the 5. Density: Metals have a high density filtrate is treated with a suitable reagent which (exceptions: sodium and potassium are less

precipitates the ore. E.g. Bauxite Al2O3.2H2O, dense than water). the ore of aluminium. 6. Ductility: Metals are usually ductile. In other words, they can be drawn into thin wires 8.5 OCCURRENCE OF ORES IN without breaking. TAMIL NADU 7. Malleability: Metals are usually malleable, i.e, they can be beaten into thin sheets Lime stone: Coimbatore, Cuddalore, Dindugul without cracking (except zinc and Gypsum: Tiruchi and Coimbatore Distiricts mercury). Titanium minerals: Kanyakumari, Tirunelveli 8. Conduction of heat and electricity: Metals and Tuticorin. are good conductors of heat and electricity; Chromite: Coimbatore and Salem district. silver and copper excel in this property Magnetite:.Dharmapuri, Erode, Salem, (exception: tungsten) Thiruvannamalai. 9. Solubility: Usually, metals do not dissolve in Tungsten: Madurai and Dindugal. liquid solvents. (Reference: mineral resources of Tamil Nadu-ENVIS Centre, Tamil Nadu) 8.6.2 Chemical Properties • Valence electrons: Atoms of metals usually 8.6 PROPERTIES OF METALS have 1,2 or 3 electrons in their outermost shell. 8.6.1 Physical properties • Formation of ions: Metals form Positive 1. Physical state: All metals are solids at room ions by the loss of electrons and hence they temperature except mercury and gallium. are electro positive. 2. Lustre: Metals possess a high lustre (called • Discharge of ions: Metals are discharged at metallic lustre). the cathode during the electrolysis of their 3. Hardness: Most of the metals are hard and compounds. strong (exceptions: sodium and potassium • Atomicity: Molecules of metals in their can be cut with a knife) vapour state are usually monoatomic. 4. Melting point and Boiling point: • Nature of oxides: Oxides of metals are Usually, metals possess high melting and usually basic.

10th Standard Science 114

10th_Science_Unit-8.indd 114 21-02-2019 18:39:02 8.7 EXTRACTIVE Temperature: 900 - 950 °C METALLURGY OF Voltage used: 5-6 V

ALUMINIUM Overall reaction: 2 Al2O3 → 4 Al +3 O2↑

Aluminium is the metal found most Electrolytic process of abundantly in the Earth’s crust. Since it is a manufacturing aluminum reactive metal, it occurs in the combined state. Bus bar The important ores of aluminium are as follows + Steel shell Carbon anode Ores of Aluminium Formula Cryolite Bauxite Al O .2H O 2 3 2 Molten aluminum – Cryolite Na3AlF6 Corundum Al O 2 3 Carbon cathode lining

Bauxite is the chief ore of aluminium. The Figure 8.10 Hall's Process extraction of aluminium from bauxite involves two steps: Aluminium is deposited at the cathode and oxygen gas is liberated at the anode. Oxygen (i) Conversion of bauxite into alumina – combines with graphite to form CO2. Baeyer’s Process The conversion of Bauxite into Alumina Physical Properties of Aluminium involves the following steps: • It is a silvery white metal Bauxite ore is finely ground and heated • It has low density (2.7) and it is light under pressure with a solution of concentrated • It is malleable and ductile caustic soda solution at 150° C to obtain sodium meta aluminate. • It is a good conductor of heat and electricity. On diluting sodium meta aluminate with water, a precipitate of aluminium hydroxide is • Its melting point is 660 °C. formed. • It can be polished to produce a shiny attractive The precipitate is filtered, washed, dried and appearance. ignited at 1000°C to get alumina. Chemical Properties of Aluminium 1000°c 2Al(OH)3 Al2O3 + 3H2O i. Reaction with air: It is not affected by dry air. On heating at 800 °C, aluminium (ii) Electrolytic reduction of alumina – burns very brightly forming it’s oxide and Hall’s Process nitride. Aluminium is produced by the electrolytic 4 Al + 3 O2 → 2 Al2O3(Aluminium oxide) reduction of fused alumina (Al2O3) in the

electrolytic cell. 2 Al + N2 → 2 AlN (Aluminium nitride) Cathode: Iron tank linked with graphite ii. Reaction with water: Water does not react Anode: A bunch of graphite rods suspended in with aluminium due to the layer of oxide molten electrolyte. on it. When steam is passed over red hot Electrolyte: Pure alumina+ molten cryolite aluminium, hydrogen is produced. + fluorspar (fluorspar lowers the 2 Al + 3 H2O → Al2O3 + 3 H2↑ fusion temperature of electrolyte) (steam) (aluminium oxide)

115 Periodic Classificaiton of Elements

10th_Science_Unit-8.indd 115 21-02-2019 18:39:03 iii. Reaction with alkalis: It reacts with strong Ores of copper Formula caustic alkalis forming aluminates. Copper pyrites CuFeS2 2 Al + 2 NaOH +2 H O → 2 NaAlO + 3 H ↑ 2 2 2 Cuprite or ruby copper Cu2O (Sodium meta aluminate) Copper glance Cu2S iv. Reaction with acids: With dilute and con.

HCl it liberates H2 gas. The chief ore of copper is copper pyrite. It yields nearly 76% of the world production of 2 Al + 6 HCl → 2 AlCl3 + 3 H2↑ (Aluminium chloride) copper. Extraction of copper from copper pyrites Aluminium liberates hydrogen on involves the following steps reaction with dilute sulphuric acid. Sulphur i. Concentration of ore: The ore is crushed dioxide is liberated with hot concentrated and the concentrated by froth floatation sulphuric acid process. 2 Al+ 3 H SO → Al (SO ) + 3 H 2 4 2 4 3 2 ii. Roasting: The concentrated ore is roasted in 2 Al + 6 H SO → Al (SO ) + 6 H O + 3 SO ↑ 2 4 2 4 3 2 2 excess of air. During the process of roasting, the moisture and volatile impurities are More to Know removed. Sulphur, phosphorus, arsenic and Dilute or concentrated nitric acid does not antimony are removed as oxides. Copper attack aluminium, but it renders aluminium pyrite is partly converted into sulphides of passive due to the formation of an oxide film copper and iron. on its surface. 2 CuFeS2 + O2 Cu2S + 2 FeS + SO2 ↑

v. As reducing agent: Aluminium is a iii. Smelting: The roasted ore is mixed with powerful reducing agent. When a mixture of powdered coke and sand and is heated in a aluminium powder and iron oxide is ignited, blast furnace to obtain matte (Cu2S + FeS) the latter is reduced to metal. This process is and slag. The slag is removed as waste. known as aluminothermic process. iv. Bessemerisation: The molten matte is Fe2O3 + 2 Al → 2 Fe + Al2O3 + Heat. transferred to Bessemer converter in order to obtain blister copper. Ferrous sulphide from Uses matte is oxidized to ferrous oxide, which is Aluminium is used in removed as slag using silica. • household utensils 2 FeS + 3 O2 2 FeO + 2 SO2 ↑ • electrical cable industry • making aeroplanes and other industrial FeO + SiO2 FeSiO3 (slag) mechine parts (Iron silicate)

2 Cu2S + 3O2 2 Cu2O + 2 SO2 ↑

8.8 EXTRACTIVE 2 Cu2O + Cu2S 6 Cu + SO2↑ METALLURGY OF COPPER (Blister copper) v. Refining: Blister copper contains 98% Occurrence: of pure copper and 2% of impurities and It was named as cuprum by the Romans is purified by electrolytic refining. This because they got it from the Island of Cyprus. method is used to get metal of a high degree Copper is found in the native state as well as of purity. For electrolytic refining of copper, combined state. we use:

10th Standard Science 116

10th_Science_Unit-8.indd 116 21-02-2019 18:39:03 Cathode: A thin plate of pure copper metal. iv) Action of Chlorine: Anode: A block of impure copper metal. Chlorine reacts with copper, resulting in the Electrolyte: Copper sulphate solution formation of copper(II) chloride.

acidified with sulphuric acid. Cu + Cl2 CuCl2 When electric current is passed through v) Action of Alkalis: the electrolytic solution, pure copper gets Copper is not attacked by alkalis. deposited at the cathode and the impurities settle at the bottom of the anode in the form of Uses of Copper: sludge called anode mud. i. It is extensively used in manufacturing electric cables and other electric appliances. Physical Properties of Copper ii. It is used for making utensils, containers, calorimeters and coins, Copper is a reddish brown metal, with iii. It is used in electroplating. high lustre, high density and high melting point iv. It is alloyed with gold and silver for making (1356°C). coins and jewels Chemical Properties of Copper 8.9 EXTRACTIVE i. Action of Air and Moisture: Copper gets METALLURGY OF IRON covered with a green layer of basic copper

carbonate in the presence of CO2 and Occurrence: moisture. Iron is the second most abundant metal

2 Cu + O2 + CO2 + H2O → CuCO3.Cu(OH)2 available next to aluminium. It occurs in nature ii. Action of Heat: On heating at different as oxides, sulphides and carbonates. The ores of temperatures in the presence of oxygen, iron are as follows:

copper forms two types of oxides CuO, Cu2O. below 1370K Ores of iron Formula 2 Cu + O2 2 CuO (copper II oxide- black) Haematite Fe2O3 above 1370K Magnetite Fe O 4 Cu + O2 2 Cu2O 3 4 (copper I oxide – red) Iron pyrite FeS2 iii. Action of Acids: Iron is chiefly extracted from haematite ore a) With dilute HCl and dilute H2SO4: (Fe2O3) Dilute acids such as HCl and H2SO4 have no action on these metals in the absence of i. Concentration by Gravity Separation: The air. Copper dissolves in these acids in the powdered ore is washed with a steam of presence of air. water. As a result, the lighter sand particles and other impurities are washed away and 2 Cu + 4 HCl + O2 (air) 2 CuCl2 + 2 H2O the heavier ore particles settle down. b) With dil. HNO3: ii. Roasting and Calcination: The Copper reacts with dil. HNO with the 3 concentrated ore is strongly heated in a liberation of Nitric Oxide gas. limited supply of air in a reverberatory 3 Cu + 8 HNO → Cu(NO ) + 2 NO ↑ + 3 3 2 furnace. As a result, moisture is driven 2H O 2 out and sulphur, arsenic and phosphorus

Cu + 2 H2SO4 → CuSO4 + SO2 ↑ + 2 H2O impurities are oxidized off.

117 Periodic Classificaiton of Elements

10th_Science_Unit-8.indd 117 21-02-2019 18:39:03 iii. Smelting (in a Blast Furnace): The (c) The Upper Region (Reduction Zone)-The charge consisting of roasted ore, coke and temperature prevails at 400°C . In this region limestone in the ratio 8:4:1 is smelted in carbon monoxide reduces ferric oxide to a blast furnace by introducing it through form a fairly pure spongy iron. the cup and cone arrangement at the top. Fe O + 3CO 400°C 2Fe + 3CO There are three important regions in the 2 3 2 The molten iron is collected at the bottom of furnace. the furnace after removing the slag. bell & hopper The iron thus formed is called pig iron. It is remelted and cast into different moulds. This iron is called cast iron.

Physical properties: Hot gases Iron ore, i. It is a lustrous metal, greyish white in colour. coke Pipe for and lime hot air ii. It has high tensility, malleability and blast ductility. iii. It can be magnetized. Slag outlet Chemical properties:

Iron outlet i. Reaction with air or oxygen: Only on heating in air, iron forms magnetic oxide.

Figure 8.11 Blast Furnace 3 Fe + 2 O2 Fe3O4 (black) ii. Reaction with moist air: When iron is (a) The Lower Region (Combustion Zone)- exposed to moist air, it forms a layer of The temperature is at 1500°C. In this region, brown hydrated ferric oxide on its surface. coke burns with oxygen to form CO when 2 This compound is known as rust and the the charge comes in contact with a hot blast phenomenon of formation of rust is known of air. as rusting. 1500°C C + O CO + Heat 2 2 . Δ 4 Fe+ 3 O2 + x H2O 2 Fe2O3 xH2O(rust) It is an exothermic reaction since heat is iii. Reaction with steam: When steam is passed liberated. over red hot iron, magnetic oxide is formed. (b) The Middle Region (Fusion Zone) – The 3 Fe + 4 H O (steam) Fe O + 4 H ↑ temperature prevails at 1000°C. In this 2 3 4 2 iv. Reaction with chlorine: Iron combines with region, CO is reduced to CO. 2 chlorine to form ferric chloride. 1000°C CO + C 2 CO – Heat 2Fe + 3Cl 2FeCl (ferric chloride) 2 Δ 2 3 Limestone decomposes to calcium oxide v. Reaction with acids: With dilute HCl and dilute H SO it liberates H gas. and CO2. 2 4 2 Fe + 2HCl FeCl + H ↑ CaCO CO – Heat 2 2 3 Δ 2 Fe + H2SO4 FeSO4 + H2 ↑ These two reactions are endothermic due to With dilute HNO3 in cold condition it gives absorption of heat. Calcium oxide combines ferrous nitrate. with silica to form calcium silicate slag. 4 Fe + 10 HNO3 → 4 Fe(NO3)2 + NH4NO3 CaO + SiO CaSiO 2 3 + 3 H2O

10th Standard Science 118

10th_Science_Unit-8.indd 118 21-02-2019 18:39:03 With con. H2SO4 it forms ferric sulphate. 8.10.2 Method of making alloys

2 Fe + 6 H2SO4 → Fe2(SO4)3 + 3 SO2 + 6 H2O (a) By fusing the metals together. E.g. Brass is made by melting zinc and copper. When iron is dipped in con. HNO3 it becomes chemically passive or inert due to the (b) By compressing finely divided metals. E.g. Wood metal: an alloy of lead, tin, bismuth formation of a layer of iron oxide (Fe3O4) on its surface. and cadmium powder is a fusible alloy. Alloys as solid solutions: Uses of iron Alloys can be considered solid solutions Pig iron (Iron with 2-4.5% of carbon): It is in which the metal with high concentration is used in making pipes, stoves, radiators, railings, solvent and other metals are solute. manhole covers and drain pipes. For example, brass is a solid solution of zinc Steel (Iron with < 0.25% of carbon): It is used (solute) in copper (solvent). in the construction of buildings, machinery, transmission cables and T.V towers and in 8.10.3 Types of Alloys making alloys. Based on the presence or absence of Iron, Wrought iron (Iron with 0.25-2% of wraught alloys can be classified into: carbon): It is used in making springs, anchors • Ferrous alloys: Contain Iron as a major and electromagnets. component. A few examples of ferrous alloys are Stainless Steel, Nickel Steel etc. 8.10 ALLOYS • Non-ferrous alloys: These alloys do not contain Iron as a major component. An alloy is a homogeneous mixture of two For example, Aluminium alloy, Copper or more metals or of one or more metals with alloy etc. certain non-metallic elements. The properties of alloys are often different Copper Alloys (Non- ferrous) from those of its components. Pure gold is too Alloys Uses soft to be used. The addition of small percentage Brass (Cu, Zn) Electrical fittings, medal, of copper enhances its strength and utility. decorative items, hardware Bronze (Cu, Sn) Statues, coins, bells, gongs 8.10.1 Amalgam Aluminium Alloys (Non- ferrous) An amalgam is an alloy of mercury with another metal. These alloys are formed through Alloys Uses metallic bonding with the electrostatic force Duralumin (Al, Mg, Aircrafts, tools, of attraction between the electrons and the Mn, Cu) pressure cookers positively charged metal ions. Silver tin amalgam Magnalium (Al, Mg) Aircraft, scientific is used for dental filling. instruments

Reasons for alloying: Iron Alloys(Ferrous) i. To modify appearance and colour Alloys Uses ii. To modify chemical activity. Stainless steel (Fe,C, Utensils, cutlery, iii. To lower the melting point. Ni,Cr) automobile parts iv. To increase hardness and tensile strength. Nickel steel Cables , aircraftparts, v. To increase resistance to electricity. (Fe,C,Ni) propeller

119 Periodic Classificaiton of Elements

10th_Science_Unit-8.indd 119 21-02-2019 18:39:03 8.11.2 Methods of preventing 8.11 CORROSION corrosion It is the gradual destruction of metals by i. Alloying: The metals can be alloyed to prevent chemical or electrochemical reaction with the process of corrosion. E.g: Stainless Steel the environment. It is a natural process which ii. Surface Coating: It involves application of a converts a metal into its oxide, hydroxide protective coating over the metal. It is of the or sulphide so that it loses its metallic following types: characteristics. a) Galvanization: It is the process of Rusting coating zinc on iron sheets by using

Air electric current. Rust Deposit Waaeter b) Electroplating: It is a method of coating DropletDroplet Fee2O3XH2O one metal over another metal by passing

2++ electric current. O FeFe (aq) 2 c) Anodizing: It is an electrochemical

– process that converts the metal surface CathodeCaathode e Anode into a decorative, durable and corrosion

– – 2+ – resistant. Aluminium is widely used for O2 + 2H2O + 4e -> 40H Fe -> Fe + 2e anodizing process. O + 4H+ + 4e– -> 2H 0 2 2 Iron d) Cathodic Protection: It is the method of controlling corrosion of a metal surface Figure 8.12 Rusting protected is coated with the metal which is easily corrodible. The easily corrodible Rust is chemically known as hydrated ferric metal is called Sacrificial metal to act as oxide (it is formulated as Fe O .xH O). Rusting 2 3 2 anode ensuring cathodic protection. results in the formation of scaling reddish brown hydrated ferric oxide on the surface of 8.12 PAMBAN BRIDGE iron and iron containing materials. It is a railway bridge which connects the 8.11.1 Types of Corrosion town of Rameshwaram on Pamban Island to mainland India. Opened on 1914, it was India’s i. Dry Corrosion or Chemical Corrosion: first sea bridge in India until the opening of the The corrosive action in the absence of BandraWorli Sea Link in 2010. We can control moisture is called dry corrosion. It is the the corrosion and renovation of historical process of a chemical attack on a metal by pamban bridge by a periodical protective a corrosive liquids or gases such as O , N , 2 2 coating which will be the strong example for SO , H S etc. It occurs at high temperature. 2 2 applied chemistry to uphold our history. Of all the gases mentioned above O2 is the most reactive gas to impart the chemical attack. ii. Wet Corrosion or Electrochemical Corrosion: The corrosive action in the presence of moisture is called wet corrosion. It occurs as a result of electrochemical reaction of metal with water or aqueous solution of salt or acids or bases. Figure 8.12 Pamban Bridge

10th Standard Science 120

10th_Science_Unit-8.indd 120 21-02-2019 18:39:03 ™ Points to Remember The charge used in the metallurgy of iron consists of roasted ore, coke and ™ Modern periodic law states that, the limestone in the ratio, 8:4:1. physical and chemical properties of the ™ Copper vessel on exposure to air and elements are the periodic functions of moisture forms a green layer on its surface their atomic numbers. due to basic copper carbonate. ™ The table in which elements are arranged ™ An alloy is a homogeneous mixture of in rows and columns in regular gradation two or more metals. is called periodic table. ™ An amalgam is an alloy of mercury with ™ Smelting is the process of reducing the another metal. E.g. Ag-Sn amalgam is roasted metallic oxide into metal in used for dental filling. molten condition. ™ The chemical name of rust is hydrated ™ Dilute or con. HNO does not attack 3 ferric oxide and its formula is Fe O .xH O. aluminium metal ,as it renders aluminium 2 3 2 passive due to oxide film formation on its surface.

TEXTBOOK EVALUATION

I. Choose the best answer. 6. In the alumino thermic process the role of 1. The number of periods and groups in the Al is _____. periodic table are______. a) oxidizing agent a) 6,16 b) 7,17 b) reducing agent c) 8,18 d) 7,18 c) hydrogenating agent 2. The basis of modern periodic law is______. d) sulphurising agent a) atomic number 7. The process of coating the surface of metal b) atomic mass with a thin layer of zinc is called______. c) isotopic mass a) painting b) thinning d) number of neutrons c) galvanization d) electroplating 3. _____ group contains the member of 8. Which of the following have inert gases halogen family. 2 electrons in the outermost shell. a) 17th b) 15th a) He b) Ne c) 18th d) 16th c) Ar d) Kr 4. _____ is a relative periodic property 9. Neon shows zero electron affinity due to a) atomic radii b) ionic radii _____. c) electron affinity d) electronegativity a) stable arrangement of neutrons 5. Chemical formula of rust is ______. b) stable configuration of electrons

a) FeO.xH2O b) FeO4.xH2O c) reduced size

c) Fe2O3.xH2O d) FeO d) increased density

121 Periodic Classificaiton of Elements

10th_Science_Unit-8.indd 121 21-02-2019 18:39:03 10. ______is an important metal to form 3. All ores are minerals; but all minerals cannot amalgam. be called as ores; a) Ag b) Hg 4. Al wires are used as electric cables due to c) Mg d) Al their silvery white colour. 5. An alloy is a heterogenous mixture of metals. II. Fill in the blanks V. Assertion and Reason 1. If the electronegativity difference Answer the following questions using the between two bonded atoms in a molecule data given below: is greater than 1.7, the nature of bonding is ______i) A and R are correct, R explains the A. ii) A is correct, R is wrong. 2. ______is the longest period in the periodical table. iii) A is wrong, R is correct. iv) A and R are correct, R doesn’t explains A. 3. ______forms the basis of modern periodic table. 1. Assertion : The nature of bond in HF molecule is ionic 4. If the distance between two Cl atoms in Cl2 molecule is 1.98Å, then the radius of Cl Reason : The electronegativity difference atom is ______. between H and F is 1.9 5. Among the given species A–,A+, and A, the 2. Assertion : Magnesium is used to protect smallest one in size is ______. steel from rusting Reason : Magnesium is more reactive than 6. The scientist who propounded the modern iron periodic law is ______. 3. Assertion : An uncleaned copper vessel is 7. Across the period, ionic radii ______covered with greenish layer. (increases,decreases). Reason : copper is not attacked by alkali 8. ______and ______are called inner transition elements. VI. Short answer questions 9. The chief ore of Aluminium is ______. 1. A is a reddish brown metal, which combines with O2 at < 1370 K gives B, a black coloured 10. The chemical name of rust is ______. compound. At a temperature > 1370 K, A gives C which is red in colour. Find A,B and III. Match the following C with reaction. 1. Galvanisation : Noble gas elements 2. A is a silvery white metal. A combines with o 2. Calcination : Coating with Zn O2 to form B at 800 C, the alloy of A is used 3. Redox reaction : Silver-tin amalgam in making the aircraft. Find A and B 4. Dental filling : Alumino thermic 3. What is rust? Give the equation for process formation of rust. 5. Group 18 : Heating in the absence 4. State two conditions necessary for rusting of elements of air iron.

IV. True or False: (If false give the correct VII. Long answer questions statement) 1. a) State the reason for addition of caustic 1. Moseley’s periodic table is based on atomic alkali to bauxite ore during purification mass. of bauxite. 2. Ionic radius increases across the period from b) Along with cryolite and alumina, another left to right. substance is added to the electrolyte

10th Standard Science 122

10th_Science_Unit-8.indd 122 21-02-2019 18:39:04 mixture. Name the substance and give b) What property forms the basis of one reason for the addition. identification? 2. The electronic configuration of metal A is c) How does the property vary in periods 2,8,18,1. and in groups? The metal A when exposed to air and moisture forms B a green layered compound. REFERENCE BOOKS A with con. H2SO4 forms C and D along with water. D is a gaseous compound. Find 1. Inorganic chemistry by PL Soni A,B,C and D. 2. Physical chemistry by Puri and Sharma 3. Explain smelting process. 3. Inorganic chemistry by Atkins

VIII. HOT questions 4. Oxford Inorganic chemistry 1. Metal A belongs to period 3 and group 13. A in red hot condition reacts with steam to INTERNET RESOURCES form B. A with strong alkali forms C. Find • https://www.webelements.com A,B and C with reactions • www.rsc.orgperiodic-table 2. Name the acid that renders aluminium passive. Why? • https://www.tcyonline.com 3. a) Identify the bond between H and F in HF molecule. CONCEPT MAP

Ore (Concentration of Ores)

Metals of high reactivity Metals of medium reactivity Metals of least reactivity

Electrolysis of molten ore Carbonate ore Sulphide ore Sulphide ore

Pure metal Calcination Roasting Roasting

Oxide of metal Metal

Reduction to metal Purification

Purification

123 Periodic Classificaiton of Elements

10th_Science_Unit-8.indd 123 21-02-2019 18:39:04