CLASS 10 Chapter 3 Metals and Non-Metals

 CHAPTER 3
METALS And NON - METALS

Metals:

• The elements which are hard, shiny can be beaten into sheets, drawn into wires and are good conductor of heat and electricity are generally metals. For example: iron, copper, gold etc.
• In nature most metals occur in the combined state as minerals and they are reactive.
• Only a few unreactive metals like gold, silver, platinum are found as free metals in the earth’s crust.
• Minerals from which metals can be profitably extracted are called ores. For example: calcium occurs in limestone (calcium carbonate) or iron in the ore hematite.

Non-metals:

• The elements which are brittle, dull cannot be beaten into sheets or drawn into wires and are poor conductors of heat and electricity are generally non-metals. For example: oxygen and nitrogen occur in free state in air and in combined state in earth’s crust. Sulphur occurs both in free and the combined state in earth’s crust.
• The noble gases, helium, neon, argon, krypton, xenon occurs only in Free State.

• Physical properties of Metals:

  • Metals are solids at room temperature, except mercury, which is liquid at room temperature.
  • They are generally hard and strong but sodium and potassium are soft solids and can be cut with a knife.
  • They are good conductor of heat and electricity. Copper is the best conductor of electricity followed by gold and aluminium.
  • Metals such as gold, silver and copper all have lustre, that is they have an ability to shine and reflect light. Therefore they are lustrous.
  • The property by virtue of which metal can be beaten into sheets is called malleability. We use aluminium foil to pack food.
  • The property by which metals can be drawn into wires is called ductility. Metals like copper, silver and aluminium can be drawn into wires.
  • Metals are sonorous. They produce sound when struck.
  • With the exceptions of sodium, potassium and mercury most of the metals have high melting and boiling point.
  • Metals have high densities.
  • Most metals have high tensile strength.

Physical properties of Non-metals:

• Non-metals are gases or solid at room temperature, except bromine which is liquid at room temperature.
• Non-metals do not have lustre except iodine and graphite.
• They are bad conductor of heat and electricity.
• Non-metals are brittle that is they are neither malleable nor ductile.
• They usually have low densities.
• Non-metals have low melting point and boiling point.
• Non-metals are non-sonorous.

• Metalloids:

  The elements which possess the properties of metals and non-metals are called metalloids.
  For example: boron, silicon, germanium, tellurium, arsenic and antimony are metalloids.  

• Chemical properties of Metals

  1. Reaction with oxygen:
  • Almost all metals combine with oxygen to form metal oxides.
  Metal + Oxygen → Metal oxide
  For e.g. 2Cu + O2 → 2CuO
  • Metal oxides are basic in nature. Some metal oxides, such as aluminium oxide, zinc oxide, etc., which react with both acids as well as bases to produce salts and water are known as amphoteric oxides.
  For e.g. Al2O3 + 6HCl → 2AlCl3 + 3H2O
• Al2O3 + 2NaOH → 2NaAlO2 + H2O
  • Most metal oxides are insoluble in water but some dissolve to form alkalis like sodium and potassium oxides.
  • Metals such as potassium and sodium react so vigorously with oxygen that they catch fire if kept in the open. So to protect them they are kept immersed in kerosene oil.
  For e.g. Na2O(s) + H2O(l) → 2NaOH(aq)
  • Anodising: Process of forming a thick oxide layer of aluminium that makes it resistant to further corrosion.
  1. Reaction with water:
  • All metals do not react with water. Those which react form metal oxide and hydrogen gas. Metal oxides that are soluble in water further form metal hydroxide.
  Metal + Water → Metal oxide + Hydrogen
  Metal oxide + Water → Metal hydroxide
  • Metals like sodium & potassium react with cold water vigorously; metals like magnesium react with hot water. Iron, zinc reacts with steam while lead, silver and gold do not react with water at all.
  2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) + heat energy
  Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)
  3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
• 1. Reaction with Dilute Acid:
  • Most metals react with acids to give a salt and hydrogen gas.
  Metal + Dilute acid → Salt + Hydrogen
  • Hydrogen gas is not evolved when a metal reacts with nitric acid. It’s a strong oxidizing agent and oxidizes hydrogen produced to water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2).
  But magnesium (Mg) and manganese (Mn) react with very dilute
  HNO3 to evolve H2 gas.
  • Aquaregia:
  • Freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1.
  • Is a highly corrosive, fuming liquid and one of the few reagents able to dissolve gold and platinum.
  • Reactivity of metals / Reactivity Series:
  • 
  • Reaction of metals with metal salts:
  • Reactive metals can displace less reactive metals from their compounds in solution or molten form.
  How do metals and non-metals react:
  • The compounds formed by the transfer of electrons from a metal to a non-metal are known as ionic or electrovalent compounds.
  • Properties of ionic compound:
  1. Physical Nature: Solid and hard due to strong inter-ionic force of attraction; generally brittle.
  2. Melting and boiling points: High melting and boiling points since a considerable force is required to break the strong inter-ionic attraction.
  3. Solubility: Generally soluble in water but insoluble in solvents such as kerosene, petrol, etc.
  4. Conduction of electricity:
  • Conducts electricity through solution due to involvement of charged particles (ions).
  • As movement of ions is not possible in solid state, due to rigid structure, do not conduct electricity.
  • In molten state this movement is overcome due to heat and thus conducts electricity.
  • Occurrence of Metals:
    • Mineral: The elements or compounds, which occur naturally in the earth’s crust.
    • Ore: Mineral that contains high percentage of metal that can be extracted profitably from it.
    • Every ore is a mineral but every mineral is not an ore.
    Obtaining metal from ore:
    • Different techniques are to be used for obtaining the metals on the basis of their reactivity.
    1. Enrichment of ore:
    • Ores mined from earth contain large amount of impurities such as sand, soil, etc. called gangue.
    • Prior to the extraction of metal, based on the differences between the physical or chemical properties of gangue and the ore, different processes are used to remove gangue.
    1. Extraction of Metal:
    2. Extraction of metals low in the Activity Series:
    • These metals are generally very unreactive.
    • Oxides of these can be reduced to metals by heating alone.
    For e.g. 2HgS(s) + 3O2 (g) + Heat → 2HgO(s) + 2SO2 (g)
    1. Extraction of Metals in the middle of the Activity Series:
    • It’s easy to obtain a metal from its oxide compared to its sulphide and carbonate.
    • Roasting is a process of converting sulphide ores into oxides by heating strongly in the presence of excess air.
    • Calcination is a process of converting carbonate ores into oxides by heating strongly in limited air.
    • Roasting
    2ZnS(s) + 3O2 (g) → 2ZnO(s) + 2SO2 (g)
  • Calcination
    ZnCO3 (s) →ZnO(s) + CO2 (g)
    • Metal oxides are then reduced to corresponding metals using suitable reducing reagents such as coke, aluminum, etc. on basis of their reactivities using displacement reactions.
    • These displacement reactions are highly exothermic; hence metals are produced in molten state.
    • Thermit reaction: Reaction of iron oxide with aluminium used to join railway tracks or cracked machine parts.
    Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) + Heat
    
    Figure 2: Steps involved in extraction of metals from ores.
    1. Extraction of metals high in the Activity Series:
    • Since these are very reactive metals and thus cannot be obtained by displacement reactions. These metals are obtained by electrolytic refining.
    • They are generally obtained by electrolysis of their molten chlorides. Metals are deposited at cathode (negatively charged), while chlorine is liberated at anode.
    At cathode Na+ + e– → Na
    At anode 2Cl– → Cl2 + 2e–
    • Aluminium is obtained by electrolytic reduction of aluminium oxide.
    
  • Figure 3: Activity Series and related metallurgy.
    1. Electrolytic Refining:
    • Metals obtained by various reduction processes contain impurities. The most widely used method for refining impure metals is electrolytic refining.
    • Apparatus setup:
    At Anode – Impure Metal
    At Cathode – Pure Metal
    Electrolyte – Solution of the metal salt
    • At Anode: Pure metal from anode dissolve into electrolyte.
    At Cathode: An equivalent amount of pure metal from electrolyte is deposited at cathode.
    • Soluble impurities go into solution; insoluble impurities settle at the bottom of anode called as anode mud.
    Corrosion:
    • The eating up of metal by the action of gases, moisture or acids present in air.
    • Corrosion of Iron:
    
    Figure 4 : Investigating the conditions under which iron rusts.
    In tube A, both air and water are present. In tube B, there is no air dissolved in the water. In tube C, the air is dry.
    • Prevention of corrosion of Iron:
    1. Painting
    2. Applying grease
    3. Galvanisation : Process of protecting steel and iron from rusting by coating them with thin layer of zinc.
    4. Chromium plating/ tin plating
    5. Alloying: Improve the properties of a metal.
    • Alloy is a homogeneous mixture of a metal and two or more other metals or non-metals.
    It has better properties than metals like in case of strength, corrosion and lower electrical conductivity& melting points.
    It is prepared by melting primary metal first and then dissolving other in definite proportion and then cooling to room temperature.
    • Some common alloys:
    1. Stainless Steel – Alloy of Fe, Ni and Cr
    2. Brass – Alloy of Cu and Zn
    3. Bronze – Alloy of Cu and Sn
    4. Solder – Alloy of Pb and Sn
    5. Amalgam – Any alloy containing mercury
    6. Alloy of Gold – Contains gold and silver/copper.