Comprehensive Notes on Chapter 3: Metals and Nonmetals

Student Examination Details and Learning Objectives

• Midterm Examination Timeline: The science examination is scheduled in two days.
• Current Status of Preparation: Zero prior preparation completed; starting with no foundational knowledge.
• Science Subject Focus: Chapter 3, titled "Metals and nonmetals" (initially referred to as chapter one, clarified as chapter three).
• Pedagogical Approach Required: Step-by-step, highly detailed, word-by-word breakdown starting from basic foundational concepts.

Foundational Classification of Matter: Metals and Nonmetals

• Atomic Basis of Matter:

  • All matter in the universe is composed of basic substances called elements.
  • An element is a pure substance consisting of only one type of atom that cannot be broken down into simpler substances by chemical means.
  • Elements are broadly classified into three main categories based on their physical and chemical properties: Metals, Nonmetals, and Metalloids.

• Definitions and Ion Formation:

  • Metals: Electropositive elements that readily lose valence electrons to form positive ions (cations) during chemical reactions.
  • Nonmetals: Electronegative elements that readily gain or share valence electrons to form negative ions (anions) or covalent compounds during chemical reactions.
  • Metalloids (Semimetals): Elements that display properties intermediate between those of metals and nonmetals (e.g., Silicon, Germanium, Arsenic, Antimony).

Physical Properties of Metals

• Malleability:

  • Malleability is the physical property of a metal that allows it to be beaten or hammered into thin sheets without fracturing.
  • Gold ($Au$) and Silver ($Ag$) represent the most malleable metals known.
  • Aluminium ($Al$) sheets and foils are extensively manufactured due to high malleability for food packaging and industrial applications.

• Ductility:

  • Ductility is the property that enables a metal to be drawn into thin, flexible wires.
  • Gold ($Au$) exhibits exceptional ductility: a wire of approximately $2\,\text{km}$ in length can be drawn from just $1\,\text{g}$ of gold.
  • Copper ($Cu$) and Aluminium ($Al$) are standard materials used in electrical wiring due to a combination of high ductility and excellent conductivity.

• Thermal and Electrical Conductivity:

  • Metals possess high thermal conductivity (ability to conduct heat) and high electrical conductivity (ability to conduct electric current).
  • Conduction occurs through the movement of free, delocalized electrons present within the metallic lattice.
  • Silver ($Ag$) is the single best conductor of heat and electricity, followed closely by Copper ($Cu$).
  • Lead ($Pb$) and Mercury ($Hg$) are comparatively poor conductors of heat relative to other metals.

• Metallic Luster:

  • Metallic luster refers to the bright, shiny surface appearance presented by metals in their pure, unreacted state.
  • Freshly cut or polished metal surfaces reflect light effectively.

• Hardness and Physical State:

  • Physical State: Almost all metals exist as solid substances at room temperature ($25\,^\circ\text{C}$).
  • Exception for State: Mercury ($Hg$) is the only metal that exists as a liquid at room temperature.
  • Hardness Range: Most metals are hard and possess high tensile strength, though hardness varies considerably across different metals.
  • Alkali Metal Exceptions: Lithium ($Li$), Sodium ($Na$), and Potassium ($K$) are soft metals that possess low densities and can easily be cut using a standard knife.

• Density and Melting/Boiling Points:

  • Metals generally exhibit high physical densities and exceptionally high melting and boiling points.
  • Tungsten ($W$) possesses an extremely high melting point of $3422\,^\circ\text{C}$, making it useful for incandescent lamp filaments.
  • Low-Melting Exceptions: Gallium ($Ga$) and Caesium ($Cs$) have exceptionally low melting points; Gallium has a melting point of $29.76\,^\circ\text{C}$ and will melt in the palm of a human hand.

• Sonority:

  • Sonority is the capability of metals to emit a deep, ringing sound when struck forcibly by a hard object.
  • Sonorous metals are utilized to manufacture items such as school bells, church bells, and strings for musical instruments.

Physical Properties of Nonmetals

• Physical States of Nonmetals:

  • Nonmetals exist across all three classical physical states at room temperature:
  • Solid State: Carbon ($C$), Sulfur ($S$), Phosphorus ($P$), Iodine ($I_2$).
  • Liquid State: Bromine ($Br_2$) is the only nonmetallic element that is liquid at room temperature.
  • Gaseous State: Hydrogen ($H_2$), Nitrogen ($N_2$), Oxygen ($O_2$), Fluorine ($F_2$), Chlorine ($Cl_2$), and Noble Gases.

• Mechanical Properties:

  • Nonmetals are non-malleable and non-ductile.
  • Solid nonmetals are brittle and shatter into smaller pieces or powder when struck with a hammer.

• Thermal and Electrical Insulations:

  • Nonmetals generally act as poor conductors (insulators) of heat and electricity because they lack free delocalized electrons.
  • Allotropic Exception: Graphite, an allotrope of carbon, acts as a good conductor of electricity due to free electrons present within its continuous planar hexagonal lattice.

• Surface Appearance:

  • Nonmetals generally lack metallic luster and display dull surfaces.
  • Exceptions: Iodine ($I_2$) crystals exhibit a natural shiny, lustrous appearance. Diamond (carbon allotrope) possesses brilliant luster due to high optical refraction.

• Density, Hardness, and Melting Points:

  • Nonmetals usually possess low physical densities, low tensile strength, and low melting and boiling points.
  • Allotropic Exception: Diamond, an allotrope of carbon featuring a 3D tetrahedral network, is the hardest naturally occurring substance and exhibits an extremely high melting point of $3550\,^\circ\text{C}$.

• Non-sonorous Nature:

  • Nonmetals do not produce a sustained ringing sound when struck.

Summary of Physical Exceptions for Exams

• Metal existing as a liquid at room temperature: Mercury ($Hg$).
• Nonmetal existing as a liquid at room temperature: Bromine ($Br_2$).
• Nonmetal possessing metallic luster: Iodine ($I_2$) and Diamond.
• Metals with melting points low enough to melt on palm: Gallium ($Ga$) and Caesium ($Cs$).
• Soft metals cut easily with a knife: Sodium ($Na$), Potassium ($K$), Lithium ($Li$).
• Nonmetal that conducts electricity: Carbon in the form of Graphite.
• Nonmetal exhibiting extreme structural hardness: Carbon in the form of Diamond.

Chemical Properties of Metals

• Reaction of Metals with Oxygen (Air):

  • General Word Equation: $\text{Metal} + \text{Oxygen} \rightarrow \text{Metal Oxide}$
  • Chemical Nature: Most metal oxides are basic oxides. When dissolved in water, basic metal oxides form alkaline solutions (hydroxides).
  • Reaction Example (Magnesium Oxidation):     $2Mg(s) + O_2(g) \rightarrow 2MgO(s)$
  • Alkalinity Demonstration:     $MgO(s) + H_2O(l) \rightarrow Mg(OH)_2(aq)$     (Magnesium hydroxide turns red litmus paper blue).

• Amphoteric Oxides:

  • Amphoteric oxides are metal oxides that exhibit both acidic and basic behaviors, reacting with both acids and strong bases to produce salt and water.
  • Aluminium Oxide ($Al_2O_3$) Reactions:     $Al_2O_3(s) + 6HCl(aq) \rightarrow 2AlCl_3(aq) + 3H_2O(l)$$Al_2O_3(s) + 2NaOH(aq) \rightarrow 2NaAlO_2(aq) + H_2O(l)$     (Product formed with sodium hydroxide is Sodium Aluminate).
  • Zinc Oxide ($ZnO$) Reactions:     $ZnO(s) + 2HCl(aq) \rightarrow ZnCl_2(aq) + H_2O(l)$$ZnO(s) + 2NaOH(aq) \rightarrow Na_2ZnO_2(aq) + H_2O(l)$     (Product formed with sodium hydroxide is Sodium Zincate).

• Oxygen Reactivity Gradient:

  • Sodium ($Na$) and Potassium ($K$) react so violently with ambient oxygen and moisture that they catch fire spontaneously in air. They are kept submerged in mineral oil / kerosene oil.
  • Iron ($Fe$) does not burn upon heating, but iron filings burn vigorously when sprinkled into a flame.
  • Copper ($Cu$) does not burn in air, but hot copper becomes coated with a black layer of Copper(II) oxide ($CuO$).
  • Gold ($Au$) and Silver ($Ag$) do not react with oxygen even at high temperatures.

• Reaction of Metals with Water:

  • General Reactions:     $\text{Metal} + \text{Water} \rightarrow \text{Metal Hydroxide} + \text{Hydrogen gas}$$\text{Metal} + \text{Steam} \rightarrow \text{Metal Oxide} + \text{Hydrogen gas}$
  • Violent Reaction with Cold Water (Sodium and Potassium):     $2K(s) + 2H_2O(l) \rightarrow 2KOH(aq) + H_2(g) + \text{Heat energy}$$2Na(s) + 2H_2O(l) \rightarrow 2NaOH(aq) + H_2(g) + \text{Heat energy}$     (The exothermic heat releases enough energy to ignite evolved hydrogen gas instantly).
  • Controlled Reaction with Cold Water (Calcium):     $Ca(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq) + H_2(g)$     (Calcium sinks initially, then floats as evolved hydrogen bubbles adhere to its surface).
  • Reaction with Hot Water (Magnesium):     Magnesium does not react with cold water; it reacts with hot water to form magnesium hydroxide and hydrogen gas, causing it to float.     $Mg(s) + 2H_2O(l) \rightarrow Mg(OH)_2(aq) + H_2(g)$
  • Reaction exclusively with Steam (Aluminium, Iron, Zinc):     These metals do not react with cold or hot water, reacting only when exposed to steam:     $2Al(s) + 3H_2O(g) \rightarrow Al_2O_3(s) + 3H_2(g)$$3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g)$
  • Inert Metals: Lead ($Pb$), Copper ($Cu$), Silver ($Ag$), and Gold ($Au$) do not react with water or steam at all.

• Reaction of Metals with Dilute Acids:

  • General Reaction:     $\text{Metal} + \text{Dilute Acid} \rightarrow \text{Metal Salt} + \text{Hydrogen gas}$
  • Hydrochloric Acid Examples:     $Mg(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + H_2(g)$$Zn(s) + 2HCl(aq) \rightarrow ZnCl_2(aq) + H_2(g)$$2Al(s) + 6HCl(aq) \rightarrow 2AlCl_3(aq) + 3H_2(g)$$Fe(s) + 2HCl(aq) \rightarrow FeCl_2(aq) + H_2(g)$
  • Nitric Acid Exception ($HNO_3$):
  • Metals generally do NOT liberate hydrogen gas when reacting with nitric acid because $HNO_3$ acts as a powerful oxidizing agent. It oxidizes generated $H_2$ into water ($H_2O$) while getting reduced into nitrogen oxides ($NO_2$, $NO$, or $N_2O$).
  • Specific Exception: Magnesium ($Mg$) and Manganese ($Mn$) react with extremely dilute ($1\%$) nitric acid to liberate hydrogen gas:       $Mg(s) + 2HNO_3(aq) \rightarrow Mg(NO_3)_2(aq) + H_2(g)$

• Aqua Regia Mixture:

  • Aqua Regia ("Royal Water") is a freshly prepared, highly corrosive liquid mixture containing concentrated Hydrochloric Acid ($HCl$) and concentrated Nitric Acid ($HNO_3$) in a precise volume ratio of $3:1$.
  • Aqua Regia can dissolve noble metals such as Gold ($Au$) and Platinum ($Pt$), which are immune to single concentrated acids.

• Displacement Reactions between Metals and Salt Solutions:

  • Principle: A more reactive metal displaces a less reactive metal from its aqueous salt solution.
  • Reaction Scheme:     $\text{Metal A} + \text{Salt of Metal B} \rightarrow \text{Salt of Metal A} + \text{Metal B}$
  • Demonstration Example:     $Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$     (A bright blue copper sulfate solution gradually turns light green as iron dissolves, and reddish-brown copper metal deposits onto the iron nail).

The Reactivity Series of Metals

• Definition: The reactivity series is an analytical arrangement of metals ranked in order of decreasing chemical activity.

• Reactivity Order (From Top/Most Reactive to Bottom/Least Reactive):

  1. Potassium ($K$) - Highest reactivity
  2. Sodium ($Na$)
  3. Calcium ($Ca$)
  4. Magnesium ($Mg$)
  5. Aluminium ($Al$)
  6. Zinc ($Zn$)
  7. Iron ($Fe$)
  8. Lead ($Pb$)
  9. Hydrogen ($H$) - Nonmetal included as reference standard for electron loss
  10. Copper ($Cu$)
  11. Mercury ($Hg$)
  12. Silver ($Ag$)
  13. Gold ($Au$) - Lowest reactivity

Chemical Properties of Nonmetals

• Reactions of Nonmetals with Oxygen:

  • General Word Equation: $\text{Nonmetal} + \text{Oxygen} \rightarrow \text{Nonmetallic Oxide}$
  • Acidic Nature: Most nonmetal oxides dissolve in water to produce acidic solutions.
  • Carbon Dioxide Acid Formation:     $C(s) + O_2(g) \rightarrow CO_2(g)$$CO_2(g) + H_2O(l) \rightarrow H_2CO_3(aq)$     (Product is Carbonic Acid).
  • Sulfur Dioxide Acid Formation:     $S(s) + O_2(g) \rightarrow SO_2(g)$$SO_2(g) + H_2O(l) \rightarrow H_2SO_3(aq)$     (Product is Sulfurous Acid).
  • Neutral Oxides: Some nonmetal oxides show neutral chemical behavior towards litmus paper (e.g., Carbon Monoxide $CO$, Water $H_2O$, Nitrous Oxide $N_2O$).

• Nonmetal Interactions with Water and Dilute Acids:

  • Nonmetals do not react with water, steam, or dilute acids to produce hydrogen gas because nonmetals cannot release electrons to reduce hydrogen ions ($H^+$) into hydrogen gas.

Chemical Bonding Between Metals and Nonmetals

• Octet Rule for Chemical Stability:

  • Atom stability is achieved when an element attains an electronic configuration matching its nearest noble gas (duplet for Helium, octet of 8 valence electrons for other noble gases).
  • Metals typically possess 1, 2, or 3 valence electrons in their outermost shell and tend to lose these electrons to form stable positively charged cations.
  • Nonmetals typically possess 4, 5, 6, or 7 valence electrons in their outer shell and tend to gain or share electrons to form stable negatively charged anions.

• Formation of Ionic (Electrovalent) Compounds:

  • An ionic bond is formed by the complete transfer of one or more valence electrons from a metal atom to a nonmetal atom, producing oppositely charged ions held together by strong electrostatic attraction.
  • Formation of Sodium Chloride ($NaCl$):
  • Sodium ($Na$): Atomic Number = 11, Configuration = 2, 8, 1.       $Na \rightarrow Na^+ + e^-$       (Sodium cation configuration = 2, 8).
  • Chlorine ($Cl$): Atomic Number = 17, Configuration = 2, 8, 7.       $Cl + e^- \rightarrow Cl^-$       (Chloride anion configuration = 2, 8, 8).
  • Ionic Combination: Electrostatic attraction yields $Na^+ + Cl^- \rightarrow NaCl$.
  • Formation of Magnesium Chloride ($MgCl_2$):
  • Magnesium ($Mg$): Configuration = 2, 8, 2.       $Mg \rightarrow Mg^{2+} + 2e^-$
  • Chlorine ($Cl$): Configuration = 2, 8, 7.       $2Cl + 2e^- \rightarrow 2Cl^-$
  • Ionic Combination: $Mg^{2+} + 2Cl^- \rightarrow MgCl_2$.

• General Physical Properties of Ionic Compounds:

  • Physical Nature: Hard, rigid crystalline solids due to powerful electrostatic attractive forces between positive and negative ions. They are brittle and fracture when pressed.
  • Melting and Boiling Points: Extremely high melting and boiling points because large amounts of thermal energy are needed to break strong inter-ionic attractive forces.
  • Solubility: Soluble in polar solvents like water, but completely insoluble in non-polar organic solvents such as kerosene, petrol, or benzene.
  • Electrical Conductivity:
  • Solid State: Do not conduct electricity because ions are fixed rigidly in crystal lattice positions and cannot move.
  • Molten State / Aqueous Solution: Conduct electricity efficiently because thermal energy or hydration overcomes electrostatic forces, allowing ions to move freely to carry electric current.

Occurrence and Metallurgy of Metals

• Key Terminology:

  • Minerals: Naturally occurring inorganic elements or chemical compounds found within the Earth's crust.
  • Ores: Minerals that contain a high concentration of a specific metal, allowing the metal to be extracted commercially and economically.
  • Gangue: Unwanted commercial impurities such as sand, soil, clay, and rocky materials present within mined ore.

• Metallurgical Steps for Metal Extraction:

  • Step 1: Enrichment (Concentration) of Ore:
  • Removal of gangue impurities using physical separation techniques based on differences in gravity, magnetic properties, or surface wetting.
  • Step 2: Extraction of Metals from Concentrated Ores:
  • Extraction of Low Reactivity Metals (Thermal Reduction):
    • Mercury extraction from Cinnabar ($HgS$):         $2HgS(s) + 3O_2(g) \rightarrow 2HgO(s) + 2SO_2(g)$$2HgO(s) \rightarrow 2Hg(l) + O_2(g)$
    • Copper extraction from Copper Glance ($Cu_2S$):         $2Cu_2S(s) + 3O_2(g) \rightarrow 2Cu_2O(s) + 2SO_2(g)$$2Cu_2O(s) + Cu_2S(s) \rightarrow 6Cu(s) + SO_2(g)$
  • Extraction of Middle Reactivity Metals (Zinc, Iron, Lead):
    • Metals existing as sulfides or carbonates are converted into metal oxides prior to reduction.
    • Roasting: Heating sulfide ores strongly in the presence of excess air:         $2ZnS(s) + 3O_2(g) \rightarrow 2ZnO(s) + 2SO_2(g)$
    • Calcination: Heating carbonate ores strongly in limited air or in the absence of air:         $ZnCO_3(s) \rightarrow ZnO(s) + CO_2(g)$
    • Reduction using Carbon (Coke):         $ZnO(s) + C(s) \rightarrow Zn(s) + CO(g)$
    • Thermite Process (Reduction using Aluminium for welding applications):         $Fe_2O_3(s) + 2Al(s) \rightarrow 2Fe(l) + Al_2O_3(s) + \text{Heat energy}$         (The exothermic reaction produces liquid iron used to join broken railway tracks).
  • Extraction of High Reactivity Metals (Electrolytic Reduction):
    • Highly reactive metals (Sodium, Calcium, Aluminium) cannot be reduced by carbon because they have a higher affinity for oxygen than carbon.
    • They are extracted by electrolysis of their molten salts.
    • Electrolysis of Molten Sodium Chloride ($NaCl$):         At Cathode (Negative Electrode): $Na^+ + e^- \rightarrow Na(s)$         At Anode (Positive Electrode): $2Cl^- \rightarrow Cl_2(g) + 2e^-$
  • Step 3: Refining of Metals (Electrolytic Refining):
  • Refining of Impure Copper:
    • Anode: Slab of impure copper metal.
    • Cathode: Thin sheet of pure copper metal.
    • Electrolyte: Acidified Copper Sulfate ($CuSO_4$) solution.
    • Reaction Mechanism: Passing current dissolves pure copper from the anode into the electrolyte, and an equivalent mass of pure copper deposits at the cathode. Insoluble impurities settle beneath the anode as Anode Mud.

Corrosion and Prevention Methods

• Definition of Corrosion:

  • Corrosion is the slow degradation and destruction of metal surfaces caused by chemical or electrochemical reactions with environmental oxygen, moisture, carbon dioxide, or acid gases.

• Important Examples of Corrosion:

  • Rusting of Iron: Formation of a reddish-brown, flaky hydrated ferric oxide layer ($Fe_2O_3 \cdot xH_2O$). Rusting strictly requires both oxygen ($O_2$) and water vapor ($H_2O$).
  • Corrosion of Copper: Copper reacts with atmospheric carbon dioxide and moisture to form a green protective surface layer of basic copper carbonate ($CuCO_3 \cdot Cu(OH)_2$).
  • Corrosion of Silver: Silver reacts with atmospheric hydrogen sulfide gas ($H_2S$) to form a dull black coating of silver sulfide ($Ag_2S$).

• Corrosion Prevention Techniques:

  • Painting, Oiling, and Greasing: Creates a protective physical barrier blocking air and moisture contact.
  • Galvanization: The process of applying a thin protective coating of Zinc ($Zn$) onto iron or steel surfaces. Zinc protects iron sacrificial-wise even if the surface coating is scratched.
  • Chrome Plating and Tinning: Depositing corrosion-resistant metals onto iron objects.
  • Anodizing: Electrochemically thickening the natural oxide surface layer on Aluminium to increase corrosion resistance.
  • Alloying: Preparing a metallic homogeneous mixture of two or more metals, or a metal and a nonmetal, to modify mechanical and chemical properties.

• Composition and Properties of Major Alloys:

  • Stainless Steel: Homogeneous mixture of Iron ($Fe$), Chromium ($Cr$), Nickel ($Ni$), and Carbon ($C$). Stainless steel is hard and completely rust-resistant.
  • Brass: Alloy of Copper ($Cu$) and Zinc ($Zn$).
  • Bronze: Alloy of Copper ($Cu$) and Tin ($Sn$).
  • Solder: Alloy of Lead ($Pb$) and Tin ($Sn$). Solder has a low melting point and is used for welding electrical wires.
  • Amalgam: Any metal alloy containing Mercury ($Hg$) as one of its constituents.
  • Gold Purity Standards: Pure gold ($24\,\text{carat}$) is too soft for practical jewelry. It is alloyed with $2\,\text{parts}$ of silver or copper to produce $22\,\text{carat}$ gold, providing required structural hardness.