chemistry - structures and properties of substances

*differentiated by their constituent particles and their bonding and arrangement

legend: section subsection keywords exam skills misconceptions & mistakes

giant ionic structure

  • constituent particles: ions (cations & anions)

  • bonding and arrangement

    • strong ionic bonding between cations and anions

  • packing

    • ions are packed in regular patterns

    • repeating lattice structure: the structure extends and repeats in three dimensions to form a lattice

  • all ions can theoretically form infinitely many ionic bonds

  • ionic bonds are the electrostatic attraction between oppositely charged ions → transfer of electrons does NOT matter

  • properties

    • hardness

      • giant ionic structure → strong ionic bonds between ions ⇒ hard

      • apply force → push same-charge ions together → repulsion ⇒ brittle

    • solubility

      • soluble in water (with exceptions)

      • insoluble in non-aqueous solvents

    • boiling point and melting point

      • melting and boiling: breaking ionic bonds

      • strong ionic bonds between ions → a lot of energy is required to break them

      • giant ionic structure → strong ionic bonds between ions ⇒ high melting point and boiling point

    • conductivity of electricity

      • requires mobile charge carriers (e.g. delocalised electrons, mobile ions)

      • solid: ions are charged but fixed → can’t complete a circuit

      • aqueous/molten: mobile ions → can complete a circuit

      • giant ionic structure → contains mobile ions in aqueous solution or molten state ⇒ conducts electricity in aqueous solution or molten state

simple molecular structure

  • constituent particles: molecules

    • a discrete group of atoms covalently bonded together

    • noble gases

  • bonding and arrangement

    • strong covalent bonds between atoms (in a molecule)

    • weak van der Waals’ forces between molecules

      • weak electrostatic attractions *NOT forces

      • strength depends on distance between molecules and molecular size

  • properties

    • hardness

      • simple molecular structure → weak van der Waals’ forces between molecules ⇒ soft

    • solubility

      • insoluble in water

      • soluble in non-aqueous solvents

      • *many exceptions

    • boiling point and melting point

      • melting/boiling: overcoming the van der Waals’ forces, NOT breaking covalent bonds

      • simple molecular structure → weak van der Waals’ forces between molecules ⇒ low boiling point and melting point

    • conductivity of electricity

      • requires mobile charge carriers (e.g. delocalised electrons, mobile ions)

      • simple molecular structure → does not contain delocalised electrons or mobile ions ⇒ does not conduct electricity
        *must write “delocalised electrons or mobile ions”, “mobile charge carriers” is not specific enough

    • *use conductivity to differentiate between giant ionic structure and simple molecular structure - generally all substances follow this rule, but there are many exceptions to solubility

giant covalent structure

  • constituent particles: atoms

  • bonding and arrangement

    • strong covalent bonds between atoms

    • atoms arranged in a regular/repeating three-dimensional lattice

    • diamond

      • an element (allotrope of carbon)

      • carbon atoms in a tetrahedral arrangement

      • strong covalent bonds between carbon atoms

    • graphite

      • an element (allotrope of carbon