C2 Structure and Bonding

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  • Structures and Bonding
    • Ionic Bonding
      • Happens between a metal and non-metal
        • The metal atoms lose electrons and become positive ions
          • Involves the transfer of electrons to make ions
          • The oppositely charged ions have a strong electrostatic force of attraction between them
          • The non-metal atoms gain electrons and become negative ions
      • Involves the transfer of electrons to make ions
      • The oppositely charged ions have a strong electrostatic force of attraction between them
      • Giant Ionic Lattices
        • In an ionic compound, millions and millions of ions are packed together in a regular lattice arrangement, joined by strong ionic bonds between oppositely-charged ions. This forms a giant 3D structure called an ionic lattice
      • Properties of ionic compounds
        • Most ionic compounds are soluble in water
        • All ionic compounds have high melting and boiling points
          • This is because in ionic compunds, the millions of ions form a giant ionic lattice, with the ions joined by strong ionic bonds
            • Therefore it requires a lot of energy to weaken the millions of bonds in an ionic compund
        • Ions are electrically charged particles
          • An electric current is the flow of electrically charged particles
            • As a solid, the ions are vibrating in fixed positions and cannot move around
              • When the ionic compound is melted, the ions can move around and conduct electricity
                • When they dissolve, the ions are free to move around in the solution
                  • Most ionic compounds are soluble in water
                  • This means that ionic compounds that are soluble in water also conduct electricity when dissolved
    • Covalent Bonding
      • A covalent bond consists of a shared pair of electrons
        • Covalent bonds are a result of electrostatic attraction between the positively-charged nuclei of the atoms and the negatively-charged shared electrons
      • Simple molecular substances
        • Low melting and boiling points
          • Although the covalent bonds within these molecules are strong, the intermolecular forces between the molecules are weak and easy to break
            • The intermolecular forces break when a substance melts or boils
        • Covalent molecules do not conduct electricity
          • This is because their particles are not charged
          • Unlike metals, covalent molecules do not have free electrons to conduct electricity
            • This is because their particles are not charged
      • Giant covalent structures
        • Diamond
          • Very high melting and boiling points
            • There are lots of strong covalent bonds that have to be broken
          • Each carbon atom forms 4 covalent bonds
          • Very hard, as all of the atoms are bonded together in a rigid network
          • Doesn't conduct heat or electricity as there are no delocalised electrons
        • Graphite
          • Each carbon atom forms 3 covalent bonds
          • Very high melting and boilng points
            • There are lots of strong covalent bonds that have to be broken
          • Soft and slippery, as the layers of atoms can slide over each other
          • Conducts heat and electricity, as there are some delocalised electrons
    • Metallic Structures
      • Metals are giant structures of atoms
      • The atoms in a pure metal are in tightly-packed layers, which form a regular lattice structure
      • The outer electrons of the metal atoms separate from the atom, becoming delocalised
        • These electrons are free to move through the structure
        • The metal atoms become positvely charged ions and are attracted to the delocalised electroms because of the elecrostatic force of attraction
          • This strong attraction is called metallic bonding
      • Properties
        • High melting points
          • This property is due to the strong attraction betwen the positively-charged metal ions and thhe sea of delocalised electrons
            • It takes a lot of energy to break down this very strong force of attraction
        • Malleable + Strong
          • When a metal is hit, the layers of metal ions are able to slide over each other, and so the structure doesn't shatter
            • The metallic bonds don't break because the delocalised electrons are free to move throughout the structure
        • Conduction
          • When a metal is heated, the delocalised electrons gain kinetic energy
            • These electrons then move faster and so transfer the gained energy throughout the metal
              • This makes heat transfer in metals very efficient
                • Delocalised electrons also conduct electricity through metals in a simliar way
    • Polymers
      • Thermosetting
        • Thermosetting polymers harden on heating, and are harder to recycle
        • They have more side chains and links to other chains
          • It is very hard for the chains to move at all, so it cannot melt
        • Once moulded, they do not soften when heated and they cannot be reshaped. Vulcanised rubber is a thermoset used to make tyres. Its polymer chains are joined together by cross-links, so they cannot slide past each other easily.
      • Thermosoftening
        • Thermosoftening polymers soften on heating and are easy to recylcle
        • They're a tangle of smooth chains, and it's easy for the molecules to slide past each other and melt
        • They can be shaped when hot. The shape will harden when it is cooled, but can be reshaped when heated up again. Poly(ethene) is a thermosoftening polymer. Its tangled polymer chains can uncoil and slide past each other, making it a flexible material.
      • A polymer's use depends on both the monomer and the process used to make it
        • High density polyethene (HDPE) is used for plastic bottles and water pipes
          • HDPE and LDPE are made from the same monomer, but by different catalysts, temperatures and pressures, making different polyethenes with different properties
            • Low density polyethene (LDPE) is used to make film and plastic bags
        • Low density polyethene (LDPE) is used to make film and plastic bags
      • Polymer molecules are long covalent chains made from carbon atoms, with various side groups attached
        • Intermolecular forces between molecules are weak, but because the molecules are so large, the effect is greater, giving them higher melting points than expected

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