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 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Chemistry 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
- IB DP Chemistry 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Chemistry 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
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:
- Opposite of malleability.
- Ionic crystals are brittle, metals are malleable.
- Brittle substances snap and break when subjected to a force because they cannot be deformed easily.
- The atoms or ions within the substance are unable to slide past each other.
2.Elasticity:
- Materials will change shape when subjected to a force and return to their original shape after the force is removed.
- In a metal spring, the metallic bonding is responsible for the elasticity.
- Rubber is elastic due to its long polymer chains being able to uncoil and coil up again.
- You can observe this property in an elastic band.
3.Plasticity: Opposite of Elasticity – (Extension of 2. Elasticity)
- Which means that the material retains its deformed shape even after the external force is removed.
- Example: Modeling Clay
4.Melting Point:
5.Electrical Conductivity:
Summary of Properties:
- 100% Metallic:
- Good heat and electricity conductors in solid and liquid state.
- High melting points (Mercury (Hg) and Alkali metals are exceptions.
- Malleable and Ductile
- 100% Covalent:
- Poor heat and electricity conductors. (Graphite and graphene is an exception)
- Generally have a low melting point
- Brittle
- >90% Ionic:
- Good electrolytes (conduct electricity when molten/aqueous solution decomposes during the process.
- Poor heat and electricity conductors in solid state.
- Quite high melting points
- 50% Ionic – 50% Covalent:
- Properties vary depending on the compound.
- Example: Aluminum Chloride $AlCl_{3}$
- Anhydrous $AlCl_{3}$, has an intermediate melting point (193°C)
- Dimerises (combine/merge) into $Al_{2}Cl_{6}$ when liquid but reverts to $AlCl_{3}$ in the vapor phase.
- Poor electricity conductor when solid
- 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:
- Steel – Iron with Carbon and other elements
- High tensile strength but tends to corrode
- Stainless Steel – Iron with Nickel or Chromium
- High strength and corrosion resistant
- Brass – Copper and Zinc
- Plumbing
- Bronze – Copper and Tin
- Coins and tools
- Pewter – Tin, Antimony and Copper
- Decorative object
- Sterling Silver – Silver and Copper
- 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.
- Thermoplastics:
- Soften when heated and harden when cooled.
- Remolded by heating
- Thermosetting Polymers:
- Prepolymers: Bakelite, polyurethane and vulcanized rubber
- In a soft solid or viscous state that changes irreversibly into hardened thermosets by curing.
- Once they are shaped during formation, they cannot be remolded.
- Elastomers:
- Flexible and can be deformed under a force but will return to nearly their original shape once the stress is released .
- 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
- Proteins:
- Basic building blocks of proteins are 2-amino acids
- Contains a carboxyl group and an amino group bonded to the same carbon atom.
- Glycine: H2N-CH2-COOH
- Alanine: H2N-CH(CH3)-COOH
- When condensed, they form two different dimers each which still contain two functional groups to allow condensation reaction to continue
- The amide bond formed is known as a peptide bond, -CO-NH-
- Polysaccharides, sugars
- Contain seven hydroxyl groups
- Two sugar molecules condense together and form a disaccharide with a glycosidic linkage:
- Example of Disaccharides: Maltose, Lactose, and Sucrose
- Polysaccharides contain many sugar units that are condensed together and used for multiple things like energy storage or cell structure, and sometimes cell recognition
- Example of Polysaccharides: Cellulose, Glycogen, and Starch
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