From models to materials – IB DP Chemistry- Study Notes | IITian Academy

From models to materials - IB DP Chemistry- Study Notes - New Syllabus 2025

From models to materials – IB DP Chemistry- Study Notes

IITian Academy excellent Introduction to the Particulate Nature of Matter – Study Notes and effective strategies will help you prepare for your IB DP Chemistry 2025 exam.

IB DP Chemistry Study Notes – All Topics

S2.4.1-2 – Bonding Continuum and Use of Triangular Bonding Diagrams

Bond Triangles: AKA vanArkel-Ketelaar Triangles:

  • Used for showing different compounds in varying degrees of ionic, metallic and covalent bonding.
  • Shows that chemical bonds are not just particular bonds of a specific type.
  • Bond types are interconnected, and different compounds have varying degrees of different bonding character (for example, polar covalent bonds).

Using Bond Triangles:

  • Find the Average electronegativity: X-AXIS

  • Electronegativity Difference: Y-AXIS    

     

X represents electronegativity value and A and B represent two bonded atoms.

Properties of Materials with Different Bonding Types:

1.Brittleness:

  1. Opposite of malleability.
  2. Ionic crystals are brittle, metals are malleable.
  3. Brittle substances snap and break when subjected to a force because they cannot be deformed easily.
  4. The atoms or ions within the substance are unable to slide past each other.

2.Elasticity:

  1. Materials will change shape when subjected to a force and return to their original shape after the force is removed.
  2. In a metal spring, the metallic bonding is responsible for the elasticity.
    1. Rubber is elastic due to its long polymer chains being able to uncoil and coil up again.
    2. You can observe this property in an elastic band.

3.Plasticity: Opposite of Elasticity – (Extension of  2. Elasticity)

  1. Which means that the material retains its deformed shape even after the external force is removed.
  2. Example: Modeling Clay

4.Melting Point:

5.Electrical Conductivity:

Summary of Properties:

  1. 100% Metallic:
    1. Good heat and electricity conductors in solid and liquid state.
    2. High melting points (Mercury (Hg)  and Alkali metals are exceptions.
    3. Malleable and Ductile
  2. 100% Covalent:
    1. Poor heat and electricity conductors. (Graphite and graphene  is an exception)
    2. Generally have a low melting point
    3. Brittle
  3. >90% Ionic:
    1. Good electrolytes (conduct electricity when molten/aqueous solution decomposes during the process.
    2. Poor heat and electricity conductors in solid state.
    3. Quite high melting points
  4. 50% Ionic – 50% Covalent:
    1. Properties vary depending on the compound.
    2. Example: Aluminum Chloride $AlCl_{3}$
      1. Anhydrous $AlCl_{3}$, has an intermediate melting point (193°C)
      2. Dimerises (combine/merge) into $Al_{2}Cl_{6}$ when liquid but reverts to $AlCl_{3}$ in the vapor phase.
      3. Poor electricity conductor when solid
      4. Behaves as an electrolyte when it forms $[Al(H_{2}O)_{6}]^{3+}$ions which are acidic

S2.4.3 – Alloys

Alloys:

  • Solid solutions.
    • Remember that a solution is a homogeneous mixture of a solute with a solvent.
    • In alloys, the solute and the solvent are both solids.
  • Two metals are mixed together in the molten state.
  • When they solidify, ions of the different metals are scattered throughout the lattice and are bound by the delocalized electrons.

Properties of Alloys:

  • Alloys are possible because of the non-directional nature of the delocalized electrons and the fact that the lattice can accommodate ions of different sizes.
  • Have properties that are distinct from their component elements due to the different packing of the cations in the lattice.
  • Often more chemically stable, stronger and resistant to corrosion.

Common Alloys:

  1. Steel – Iron with Carbon and other elements
    1. High tensile strength but tends to corrode
  2. Stainless Steel – Iron with Nickel or Chromium
    1. High strength and corrosion resistant
  3. Brass – Copper and Zinc
    1. Plumbing
  4. Bronze – Copper and Tin
    1. Coins and tools
  5. Pewter – Tin, Antimony and Copper
    1. Decorative object
  6. Sterling Silver – Silver and Copper
    1. Jewelry and Art objects

S2.4.4 – Polymers

Polymers:

  • Made of many repeating units called ‘Monomers’
    • Joined together chemically to form macromolecules with high molar masses.
  • Monomers may bond through addition reactions. [e.g. Poly(ethene)]
  • Form addition polymers or through condensation reactions. [e.g. proteins (formed from amino acid monomers) and polysaccharides (formed from monosaccharide monomers such as glucose)
  • Many polymers occur naturally.
    • Man-made: Polystyrene and Nylon

Properties of Polymers:

  • Properties can be subdivided into thermoplasticsand thermosetting polymers.
  1. Thermoplastics:
    1. Soften when heated and harden when cooled.
    2. Remolded by heating
  2. Thermosetting Polymers:
    1. Prepolymers: Bakelite, polyurethane and vulcanized rubber
    2. In a soft solid or viscous state that changes irreversibly into hardened thermosets by curing.
      1. Once they are shaped during formation, they cannot be remolded.
  3. Elastomers:
    1. Flexible and can be deformed under a force but will return to nearly their original shape once the stress is released .
    2. Rubber is an elastomer

Addition Polymers:

  • Alkenes readily undergo addition reactions by breaking their double bond.
  • Can be joined together to produce long chains known as polymers.
  • The alkene used in the reaction is known as the monomer and its chemical nature will determine the properties of the polymer.

Economic Impact:

  • Alkenes are used as starting materials in the manufacture of many industrially important chemicals.
  • Polymers are a major product of the organic chemical industry.
  • Most of our common and useful plastics are polymers of alkenes.

Polypropylene: Addition Polymer

  • Propene polymerizes to form polypropene  AKA polypropylene.
  • Used in the manufacture of clothing.
  • More specifically the production of thermal wear.

Polychloroethene:

  • Known as PVC, poly vinyl chloride.
  • One of the world’s most important plastics.
  • Used in construction materials, packaging, and electrical cable sheathing.
  • Its synthesis produces dioxins which are  toxic and are linked to a variety of cancers.

TEFLON:

  • Polytetrafluoroethene is known as PTFE
  • Often marketed as Teflon.

S2.4.5 – [HL] Condensation Polymers

Condensation Polymers:

  • Formed by a reaction that joins monomers and also produces small molecules (H2O, NH3 or HCl) as a condensation product.
  • The formation of an ester from an alcohol and a carboxylic acid is an example of a condensation reaction: as well as the ester, water is formed as the condensation product
  • To form condensation polymers monomers must contain two functional groups.

Monomers that may form Condensation Polymers:

  • Carboxyl group        -COOH
  • Hydroxyl group        -OH
  • Acyl group                -COCl
  • Amine group                -NH2

Terylene:

  • Condensation polymer of terephthalic acid and ethylene glycol

Polyamide:

  • Formed by condensing amines with either dicarboxylic acids or diacyl chlorides.
  • Example: Nylon 6,6 is prepared by reacting, Hexane 1,6-dioic acid and 1,6 diaminohexane

Natural Condensation Polymers:

  • Biological macromolecules are natural condensation molecules.
  • Example: Proteins and Polysaccharides
  1. Proteins:
    1. Basic building blocks of proteins are 2-amino acids
    2. Contains a carboxyl group and an amino group bonded to the same carbon atom.
      1. Glycine: H2N-CH2-COOH
      2. Alanine: H2N-CH(CH3)-COOH
    3. When condensed, they form two different dimers each which still contain two functional groups to allow condensation reaction to continue
    4. The amide bond formed is known as a peptide bond,         -CO-NH-
  2. Polysaccharides, sugars
    1. Contain seven hydroxyl groups
    2. Two sugar molecules condense together and form a disaccharide with a glycosidic linkage:
    3. Example of Disaccharides: Maltose, Lactose, and Sucrose
    4. Polysaccharides contain many sugar units that are condensed together and used for multiple things like energy storage or cell structure, and sometimes cell recognition
    5. Example of Polysaccharides: Cellulose, Glycogen, and Starch

  1.  

Hydrolysis of Condensation Polymers:

  • The reverse reaction of condensation polymers
  • Polyesters, polyamides, and polysaccharides can be broken down in the presence of water into their monomers constituents.
  • With glass (in vitro) it requires heat and acid or alkaline conditions.
    • Example: proteins hydrolyse in the presence of warm hydrochloric acid to form amino acids
  • In living (in vivo) enzymes catalyze hydrolysis reactions.
    • Example: Starch is hydrolysed by enzymes called amylases to from glucose
  • Biodegradable polymers utilize enzymes in living organisms as well as physical sources or energy, like UV, to decompose naturally
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