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Chapter 6: Molecular, Polymer and Giant Covalent Structure

6.1-Simple Molecular Substances

Learn these examples of simple molecular substances

  • Simple molecular substances are made up of molecules containing a few atoms joined together by covalent bonds. Here are some common examples that you should know

    • Hydrogen

      • Hydrogen atoms have just one electron.

      • They only need one more to complete the first shell so they often form single covalent bonds, either with other hydrogen atoms or with other elements, to achieve this.

    • Chlorine

      • Each chlorine atom needs just one more electron to complete the outer shell so two chlorine atoms can share one pair of electrons and form a single covalent bond

    • Oxygen

      • Each oxygen atom needs two more electrons to complete its outer shell so in oxygen gas two oxygen atoms share two pairs of electrons with each other making a double covalent bond

    • Nitrogen

      • Nitrogen atoms need three more electrons so two nitrogen atoms share three pairs of electrons to fill their outer shells

      • This creates a triple bond

    • Methane

      • Carbon has four outer electrons, which is half a full shell

      • It can form four covalent bonds with hydrogen atoms to fill up its outer shell

    • Water

      • In water molecules, the oxygen shares a pair of electrons with two H atoms to form two single covalent bonds

    • Hydrogen Chloride

      • This is very similar to H2 and Cl2.

      • Again, both atoms only need one more electrons to complete their outer shells

Properties of simple molecular substances

  • Substances containing covalent bonds usually have simple molecular structures, like the examples above

  • The atoms within the molecules are held together by very strong covalent bonds

    • By contrast, the forces of attraction between these molecules are very weak

6.2-Polymers and Giant Covalent Structures

Polymers are long chains of repeating units

  • In a polymer, lots of small units are linked together to form a along molecule that has repeating sections

  • All the atoms in a polymer are joined by strong covalent bonds

  • Instead of drawing out a whole long polymer molecule(which can contain thousands or millions of atoms), you can draw the shortest repeating section, called the repeating unit:

    • This polymer is called poly(ethene)

    • The bonds through the brackets join up to the next repeating unit

    • The bit in brackets is the repeating unit

    • n is a large number

      • It tells you that the unit’s repeated lots of times

  • So for poly|(ethene), the molecular formula of the polymer is C2H4n

  • The intermolecular forces between polymer molecules are larger than between simple covalent molecules, so more energy is needed to break them

    • This means most polymers are solid at room temperature

  • The intermolecular forces are still weaker than ionic or covalent bonds, so they generally have lower boiling points than ionic or giant molecular compounds

Giant covalent structures are macromolecules

  • In giant covalent structures, all the atoms are bonded to each other by strong covalent bonds

  • They have very high melting and boiling points as lots of energy is needed to break the covalent bonds between the atoms

  • They don’t contain charged particles, so they don’t conduct electricity-not even when molten

    • Except for a few weird exceptions such as graphite

  • The main examples that you need to know about are diamond and graphite, which are both made from carbon atoms only and silicon dioxide

    • Diamond:

      • Each carbon atoms forms four covalent bonds in a very rigid giant covalent structure

    • Graphite:

      • Each carbon atom forms three covalent bonds to create layers of hexagons

      • Each carbon atom also has one delocalised(free) electron

    • Silicon dioxide:

      • Sometimes called silica, this is what sand is made of

      • Each grain of sand is one giant structure of silicon and oxygen

Chapter 6: Molecular, Polymer and Giant Covalent Structure

6.1-Simple Molecular Substances

Learn these examples of simple molecular substances

  • Simple molecular substances are made up of molecules containing a few atoms joined together by covalent bonds. Here are some common examples that you should know

    • Hydrogen

      • Hydrogen atoms have just one electron.

      • They only need one more to complete the first shell so they often form single covalent bonds, either with other hydrogen atoms or with other elements, to achieve this.

    • Chlorine

      • Each chlorine atom needs just one more electron to complete the outer shell so two chlorine atoms can share one pair of electrons and form a single covalent bond

    • Oxygen

      • Each oxygen atom needs two more electrons to complete its outer shell so in oxygen gas two oxygen atoms share two pairs of electrons with each other making a double covalent bond

    • Nitrogen

      • Nitrogen atoms need three more electrons so two nitrogen atoms share three pairs of electrons to fill their outer shells

      • This creates a triple bond

    • Methane

      • Carbon has four outer electrons, which is half a full shell

      • It can form four covalent bonds with hydrogen atoms to fill up its outer shell

    • Water

      • In water molecules, the oxygen shares a pair of electrons with two H atoms to form two single covalent bonds

    • Hydrogen Chloride

      • This is very similar to H2 and Cl2.

      • Again, both atoms only need one more electrons to complete their outer shells

Properties of simple molecular substances

  • Substances containing covalent bonds usually have simple molecular structures, like the examples above

  • The atoms within the molecules are held together by very strong covalent bonds

    • By contrast, the forces of attraction between these molecules are very weak

6.2-Polymers and Giant Covalent Structures

Polymers are long chains of repeating units

  • In a polymer, lots of small units are linked together to form a along molecule that has repeating sections

  • All the atoms in a polymer are joined by strong covalent bonds

  • Instead of drawing out a whole long polymer molecule(which can contain thousands or millions of atoms), you can draw the shortest repeating section, called the repeating unit:

    • This polymer is called poly(ethene)

    • The bonds through the brackets join up to the next repeating unit

    • The bit in brackets is the repeating unit

    • n is a large number

      • It tells you that the unit’s repeated lots of times

  • So for poly|(ethene), the molecular formula of the polymer is C2H4n

  • The intermolecular forces between polymer molecules are larger than between simple covalent molecules, so more energy is needed to break them

    • This means most polymers are solid at room temperature

  • The intermolecular forces are still weaker than ionic or covalent bonds, so they generally have lower boiling points than ionic or giant molecular compounds

Giant covalent structures are macromolecules

  • In giant covalent structures, all the atoms are bonded to each other by strong covalent bonds

  • They have very high melting and boiling points as lots of energy is needed to break the covalent bonds between the atoms

  • They don’t contain charged particles, so they don’t conduct electricity-not even when molten

    • Except for a few weird exceptions such as graphite

  • The main examples that you need to know about are diamond and graphite, which are both made from carbon atoms only and silicon dioxide

    • Diamond:

      • Each carbon atoms forms four covalent bonds in a very rigid giant covalent structure

    • Graphite:

      • Each carbon atom forms three covalent bonds to create layers of hexagons

      • Each carbon atom also has one delocalised(free) electron

    • Silicon dioxide:

      • Sometimes called silica, this is what sand is made of

      • Each grain of sand is one giant structure of silicon and oxygen

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