Metals and non-metals… Reactivity.. Why? How?

Noble gas configuration Noble gases have a completely filled valence shell. Octet electronic configuration similar to noble gases is found to be stable. Erratum: Please note that the no: of electrons in M shell of Argon is 8, not 18

Why do elements differ in their reactivity? The elements differ in their reactivity due to their tendency to attain a completely filled valence shell.

How do metals and non-metals react? Valence electrons 1, 2, 3 shows tendency to lose electrons from the valence shell. Metals are electropositive Valence electrons 5, 6, 7 shows tendency to gain electrons to the valence shell. Non-metals are electronegative

How do metals and non-metals react?

Sodium & Chlorine

Formation of Sodium Chloride

Formation of Magnesium Chloride

Ionic / Electrovalent bond The chemical bond formed by the transfer of electrons from the valence shell of a metal to the valence shell of a non-metal, thereby both elements acquiring nearest noble gas configuration is called ionic or electrovalent bond. Ionic bond is formed between metals and non-metals.

Ionic/ electrovalent compound The compounds formed through ionic bonding are called ionic compounds or electrovalent compounds. eg NaCl , CaO, MgO, MgCl2, ZnCl2 etc

Properties of ionic compounds Ionic compounds are generally hard, brittle crystalline solids (due to strong electrostatic force of attraction). Ionic compounds have high melting and boiling points (due to strong inter-ionic attraction). Ionic compounds are soluble in polar solvents like water and insoluble in non-polar solvents like kerosene and petrol. Ionic compounds in the solid state do not conduct electricity. They conduct electricity only in the molten state or in aqueous solutions due to the availability of mobile charged ions.

Occurrence of metals Free State: Metals found in the elemental form. The metals at the bottom of the reactivity series are least reactive. Example:- Au, Ag, Pt, Cu. Combined state: Metals found in the form of compound as oxides, sulphides, carbonates etc. Eg :Cu, Ag, Na, K, Ca, Mg, Al, Zn, Fe, Pb etc. Minerals: elements or compounds found naturally in the earth’s crust. Ores: the minerals from which metals can be extracted profitably. Gangue: It is the impurities present in the ore particles. Flux: It is a substance used to remove impurities. Slag: It is the molten fusible substance formed when flux reacts with gangue. 9/19/2018

Extraction of Metals Metallurgy: Several steps involved in the extraction of pure metal from its ores. Steps involved in extraction: Enrichment of ore Extraction of metal from the enriched ore Refining of metals 9/19/2018

Enrichment of ore

Enrichment / Concentration of the ore The process of removing impurities from the ores. Gangue: Unwanted substances which contaminate ores. Eg: unwanted rocks soil, sand etc. These have to be removed so that the mineral ore is concentrated with higher percentage of metal. Ores are mined from deep within the earth’s crust in the form of rocks. The minerals are embedded in these rocks. The rocks are first crushed into smaller pieces by crushers and then powdered. Physical or chemical properties of the gangue and the ore decide the method employed for concentration of the ore. 9/19/2018

Methods of concentrating the ore Depending on the type of ore, hydraulic washing, froth floatation process, magnetic separation and chemical separation techniques are applied for concentrating an ore.

Extraction of metal from concentrated ore

METAL EXTRACTION PROCESS BASED ON REACTIVITY

How are metals classified based on their reactivity? (a) Metals of high reactivity K, Na, Ca, Mg, Al (b) Metals of medium reactivity Zn, Fe, Pb, Cu (c) Metals of low reactivity. Ag, Au

STEPS INVOLVED IN EXTRACTION OF METALS ORE CONCENTRATION OF ORE METALS OF HIGH REACTIVITY METALS OF MEDIUM REACTIVITY METALS OF LOW REACTIVITY ELECTROLYSIS OF MOLTEN ORE SULPHIDE ORES CARBONATE ORE SULPHIDE ORE ROASTING CALCINATION ROASTING PURE METAL METAL REFINING OXIDE OF METAL REDUCTION TO METAL PURIFICATION OF METAL

1. Extracting metals low in the reactivity series (very unreactive) Ores can be reduced to metal by heating alone. Eg 1: Mercury from its ore Cinnabar (HgS) a. Conversion of sulphide to oxide 2HgS(s) + 3O2 (g) heat→ 2HgO(s) + 2SO2 (g) b. Decomposition of oxide to metal 2HgO(s) heat→ 2Hg(l) + O2(g) Eg 2: Copper from its ore copper glance (Cu2S) 2Cu2S(s) + 3O2 (g) heat→ 2Cu2O(s) + 2SO2 (g) 2Cu2O + Cu2S heat→ 6Cu(s) + SO2 (g) 9/19/2018

2. Extracting Metals in the middle of the reactivity series (Fe, Zn, Pb) Fe, Zn, Pb are moderately active elements. Found as sulphides or carbonates in nature. It is easier to extract metals from the oxides than from sulphides or carbonates. Step 1. The metal sulphides and carbonates are converted to metal oxides. Step 2. The metal oxides are then reduced to the corresponding metals by using suitable reducing agents like carbon or highly reactive metals like Al. 9/19/2018

Step 1: Conversion of the carbonates and sulphides to oxides. By Roasting Calcination 9/19/2018

Roasting Used to convert sulphide ores into oxides. Done by heating the sulphide ore strongly in the presence of excess air, so that oxygen gets added to form the corresponding oxides. Sulphur impurities escape as gas.

Calcination Usually, carbonate ores (or ores containing water) are calcined to drive out carbonate and moisture impurities. In this process the ore is heated to a high temperature in the absence of air, or where air does not take part in the reaction.

Roasting vs Calcination Heating in the presence of air Heating in the absence of air Sulphide ores are roasted Carbonate ores are calcined Sulphur dioxide is released Carbon dioxide is released Not used for dehydrating an ore Can be used to drive out moisture from an ore

Step 2. Reduction of metallic oxides to metals The oxide obtained by calcination or roasting is then reduced to the metal using a reducing agent. Metal oxide + reducing agent → Metal + oxidized reducing agent 1. Using carbon. (Usually in the form of coke, or carbon monoxide).

Reduction…. 2. Using highly reactive metals Highly reactive metals such as sodium, calcium, aluminium, etc., are used as reducing agents because they can displace metals of lower reactivity from their compounds. Oxides of manganese (MnO2) and Chromium (Cr2O3) are reduced to the metal by heating with more active metals like aluminium. Eg: 1. Heating manganese dioxide with aluminium powder    3MnO2(s) + 4Al(s) ) Heat→ 3Mn(l) + 2Al2O3(s) + Heat 2.Thermit reaction The reaction of iron(III) oxide (Fe2O3) with aluminium is used to join railway tracks or cracked machine parts. Fe2O3(s) + 2Al(s) ) Heat→ 2Fe(l) + Al2O3(s) + Heat

3. Extraction of metals towards top of the reactivity series Metals high in the reactivity series are very reactive and cannot be obtained from their compounds by heating with carbon. These metals have more affinity for oxygen than carbon. These metals are obtained from their compounds by electrolytic reduction. Sodium, magnesium and calcium are obtained by the electrolysis of their molten chlorides. The metal gets deposited at the cathode.

Extraction of Sodium from NaCl At cathode Na+  + e-  →  Na At anode 2Cl-    →   Cl2 + 2 e-

Refining of metals

ELECTROLYTIC REFINING Refining by electrolysis. A thick block of the impure metal is made anode. A thin strip of the pure metal is made cathode. A water soluble salt of the metal to be refined is taken as electrolyte. 9/19/2018

Electrolytic refining of copper A thick block of impure copper is made the anode. A thin strip of pure copper is made the cathode. The electrolyte is acidified copper sulphate solution. When electric current is passed through the electrolyte, pure copper from the anode dissolves into the electrolyte. An equivalent amount of pure copper from the electrolyte is deposited on the cathode. Soluble impurities go into the solution, while insoluble impurities settle down as anode mud.

Corrosion The process of slow wasting away of metal by the action of atmospheric gases and moisture is called corrosion. Silver objects : Black deposit (Silver sulphide) Copper objects : Green deposit (Basic copper carbonate) Iron objects : Brown flaky deposit (Hydrated ferric oxide) 9/19/2018

Conditions necessary for corrosion of iron Rusting agents Air (oxygen) Moisture (water). Prevention of corrosion Painting: When a coat of paint is applied to the surface of an iron object, then air and moisture cannot come in contact with the iron object and hence no rusting takes place. Applying grease or oil: When some grease or oil is applied to the surface of an iron object, then air and moisture cannot come in contact with it and hence rusting is prevented. 9/19/2018

Prevention of Corrosion Galvanizing: Coating iron objects with a thin layer of zinc. Chrome plating: Coating iron objects with chromium by electrolysis. Anodising: Making thicker layer of oxide on aluminium. Alloying: Making homogeneous mixtures of two or more metals or a metal with a non-metal. It is prepared by first melting the primary metal and then dissolving the other elements in it in definite proportions. It is then cooled to room temperature. 9/19/2018

Why do we make alloys? For altering the properties Increasing hardness: Adding carbon to iron. Making corrosion resistant: Adding Ni and Cr to iron (stainless steel) Lowering melting point: Mixing tin + lead (solder ) Reducing electrical conductivity: Mixing Cu and Zn to make Brass Reducing reactivity: Adding mercury to sodium. Alloys of metal with mercury are called Amalgams. 9/19/2018