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Giant Structures

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Apuntes de la lección

Introduction to Giant Structures

  • Giant covalent structures contain billions of non-metal atoms joined by strong covalent bonds in a giant lattice.
  • Diamond and graphite are allotropes of carbon – same element, different bonding arrangements.
  • Giant structures have very high melting points due to many strong bonds.
  • Silicon(IV) oxide (SiO₂) is also a giant covalent compound.

Diamond – Structure & Properties

  • Each carbon atom bonds to four others in a tetrahedral arrangement.
  • All bonds are identical, very strong covalent bonds; no intermolecular forces.
  • Does not conduct electricity – all outer electrons are used in bonds.
  • Extremely hard and dense – used in cutting tools and drills.
  • Very high melting point – many strong bonds need lots of energy to break.
  • Hard but brittle (can be smashed with a hammer).

Diamond — giant covalent structure

Diamond — giant covalent structureCCCCCCCCCCCCCCCarbon atomStrong covalentbondEach carbonbonds to 4others

Graphite – Structure & Properties

  • Each carbon atom bonds to three others, forming layers of hexagons.
  • One delocalised electron per carbon atom is free to move between layers.
  • Conducts electricity – delocalised electrons carry charge.
  • High melting point – strong covalent bonds within layers.
  • Slippery – layers held by weak intermolecular forces can slide over each other.
  • Used as a lubricant, in pencils, and as electrodes (unreactive, conducts).

Graphite — giant covalent structure (layers)

Graphite — giant covalent structure (layers)e⁻e⁻e⁻e⁻e⁻e⁻DelocalisedelectronLayer of carbonatomsWeak forcesbetween layers

Silicon(IV) Oxide (SiO₂)

  • Giant covalent structure – each Si bonds to 4 O atoms, each O bonds to 2 Si atoms.
  • Forms a tetrahedral arrangement similar to diamond.
  • Very hard, high melting point, insoluble in water, does not conduct electricity.
  • Occurs naturally as sand and quartz.
  • Used to make sandpaper and to line furnaces (cheap, heat-resistant).

Silicon(IV) oxide (SiO₂) — giant covalent structure

Silicon(IV) oxide (SiO₂) — giant covalent structureOOOOOOOOSiSiSiSiSiSiSiSiSilicon atomOxygen atomEach Si bonds to4 O atoms

Metallic Bonding

  • Metals consist of a giant lattice of positive metal ions surrounded by a ‘sea of delocalised electrons’.
  • The metallic bond is the electrostatic attraction between positive ions and delocalised electrons.
  • High melting/boiling points – strong metallic bonds require lots of energy to break.
  • Good conductors of heat and electricity – delocalised electrons move freely.
  • Malleable and ductile – layers of ions can slide over each other without breaking bonds.

Metallic bonding

Magnesium — metallic bondinge⁻e⁻e⁻e⁻e⁻e⁻e⁻e⁻e⁻Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Mg²⁺Positive metalionSea ofdelocalisedelectrons

Diapositivas

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Preguntas de práctica

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  1. 1.Which statement about carbon allotropes is correct?

    Medium
    • ADiamond contains carbon atoms bonded to three other carbon atoms.
    • BGraphite is a good conductor of electricity because of the presence of mobile ions.
    • CDiamond is used as a lubricant because of the weak intermolecular forces between its layers.
    • DGraphite is a good conductor of electricity because it contains delocalised electrons.
  2. 2.Which row describes how graphite can be used in electrolysis?

    Medium
    • ADelocalised electrons – conducts electricity
    • BDelocalised electrons – acts as an insulator
    • CLow melting point – acts as an insulator
    • DLow melting point – conducts electricity
  3. 3.Which statement correctly describes the bonding in metals?

    Easy
    • AA lattice of negative ions in a 'sea of electrons'.
    • BA lattice of positive ions in a 'sea of electrons'.
    • CA lattice of neutral atoms with delocalised electrons.
    • DA lattice of negative ions with delocalised electrons.
  4. 4.Which row provides a correct description of the properties of metals?

    Easy
    • Amelting point high, boiling point low, conducts electricity yes
    • Bmelting point low, boiling point high, conducts electricity yes
    • Cmelting point low, boiling point low, conducts electricity no
    • Dmelting point high, boiling point high, conducts electricity yes
  5. 5.What other property does graphite have that makes it useful for electrodes?

    Medium
    • AGraphite is an unreactive substance and doesn’t react with the electrolyte.
    • BGraphite is soft and easy to shape into electrodes.
    • CGraphite has a low melting point due to the weak forces in between the layers.
    • DGraphite dissolves readily in water.
  6. 6.Which of the following statements about graphite and diamond are incorrect? 1 They are allotropes of carbon. 2 They both conduct electricity. 3 They form different numbers of bonds within their structures. 4 They have different uses.

    Medium
    • A2 and 3
    • B2 only
    • C1, 3 and 4
    • D2 and 4
  7. 7.Which statement correctly describes the structure of macromolecules?

    Medium
    • AGiant molecular crystal which is held together by weak intermolecular forces.
    • BGiant molecular crystal which is held together by strong ionic bonds.
    • CGiant molecular crystal which is held together by weak metallic bonds.
    • DGiant molecular crystal which is held together by strong covalent bonds.
  8. 8.Which statement about graphite and diamond is not correct?

    Medium
    • AGraphite is a good lubricant due to the weak forces in between the layers.
    • BDiamond is used as a drill tip because it is an extremely hard substance.
    • CGraphite has a low melting point due to the weak forces in between the layers.
    • DDiamond is an allotrope of carbon.

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