Bonding

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  • Bonding
    • Ionic Bonding
      • Ions are formed when one or more electrons are transferred from one atom to another.
      • Electrostatic attraction holds positive and negative ions together
      • These bonds are very strong
      • When oppositely charged ions form and ionic bonds. A ionic compound is formed.
      • The formula of an ionic compound tells you what is in the compound. The negative charges will always balance the positive charges
        • So the compound has no overall charge
      • Giant Ionic Lattice
        • Ionic crystals are giant ionic lattices
        • These are called giant because they are made up of the same basic unit repeated over and over again
        • Different ionic compounds have different shaped structures, but they are all still giant lattices.
      • Behaviour of ionic compounds
        • Electrical Conductivity
          • Ionic compounds only conduct electricity when they are either in solution or molten
          • Ions in liquids are free to move so they can carry a current meaning that they can conduct electricity
            • In a solid the ions are in a fixed position so they cannot move
              • Solid ionic compounds do not conduct electricity
                • Ionic compounds only conduct electricity when they are either in solution or molten
        • Melting point
          • Ionic compounds have high melting points
          • The giant ionic lattice is held together by strong electrostatic forces
            • This means that a lot of energy is required to overcome these forces
              • Resulting in high melting points for ionic compounds
        • Solubility
          • Ionic compounds tend to dissolve in water
            • This is due to the polarity of water molecules
              • The water molecules pull the ions away from the lattice. Causing it to dissolve
    • Covalent Bonding
      • Molecules
        • Smallest part of the compound which can take part in chemical reactions.
          • They are formed when two or more atoms bond together
            • Molecules are held together by strong covalent bonds
      • Single bonds
        • In covalent bonds, two atoms share electrons until they both have full outer energy levels
        • In a single bond there is only one shared pair of electrons in each bond
      • Double or triple bonds
        • Where there are two or more shared pairs of electrons between two atoms
      • Behaviour of simple covalent bonds
        • Simple covalent compounds
          • have strong bonds within the molecule but weak intermolecular forces between the molecules
          • Their physical properties are determined by the bonding in the compound
        • Electrical Conductivity
          • Simple covalent compounds don't conduct electricity
            • Because there are no free ions or electrons to carry the charge
        • Melting Point
          • Simple covalent compounds have low melting points
            • Because the weak intermolecular forces between molecules are easily broken
        • Solubility
          • Some simple covalent compounds dissolve in water depending on how polarised the molecules are
    • Giant Covalent Structures
      • Graphite (Carbon)
        • The carbon atoms in graphite are arranged in sheets of flat hexagons covalently bonded with 3 bonds each
          • The fourth outer electron is delocalised.
            • These delocalised electrons are free to move so allow a current to flow
              • Graphite can conduct electricity
          • The sheets of hexagons are bonded together by weak van der waals forces
            • The layers are quite far apart compared to the length of the covalent bonds
              • Graphite has a low density and so is used to make lightweight sports equipment
          • The strong covalent bonds mean that graphite has a high melting point
            • It sublimes at over 3900K
          • Graphite is insoluble in any solvent as the covalent bonds are too strong to break
        • The weak IMF can be easily broken so the sheets of carbon can slide over each other
      • These have huge networks of covalently bonded atoms.
      • Diamond (Carbon)
        • Each carbon atom is covalently bonded to four other carbon atoms.
          • It has a very high melting point
            • Sublimes at over 3800K
            • Diamond is insoluble in any solvent just like graphite
        • The carbon atoms arrange themselves into a tetrahedral shape
          • Crystal lattice
          • It is very hard
            • Used for tips of drills
          • Good thermal conductor
            • Vibrations travel easily through the stiff lattice
            • Can't conduct electricity
              • All electrons are held in bonds non are delocalised
    • Dative Covalent Bond
      • It is the same as an ordinary covalent bond but both shared electrons are provided by the same atom.
      • There is one dative covalent bond in the ammonium ion
        • Between the nitrogen atom and one of the hydrogen atoms
        • Both of the electrons come from the nitrogen atom
    • Intermolecular Forces
      • Van der Waals
        • The constantly moving electrons within charge clouds can induce a dipole on molecules  close by.
          • The two dipoles are attracted to each other
          • Because the electrons are constantly moving, dipoles are constantly being created and distroyed
          • Even though the dipoles keep changing, the overall effect is that the atoms are attracted to each other
          • The stronger the intermolecular forces, the higher the boiling and melting point of a substance because more energy is needed to overcome them
        • Not all Van der Waals forces are the same strength
          • Larger molecules have larger electron clouds so have stronger forces.
            • Molecules with a larger surface area also have stronger forces
              • There is a bigger area for the forces to act upon
              • More exposure of the electron cloud
      • Permanent dipole- dipole forces
        • The charges on polar molecules cause weak electrostatic forces of attraction between molecules
          • If you put a charged rod next to a polar liquid such as water, the liquid will move towards he rod due to the permanent dipoles within the liquid
            • This will happen if the rod is positively or negatively charged as the polar molecules in the liquid can turn around so that they are attracted to the rod
      • Hydrogen bonding
        • The strongest intermolecular force
          • Only occurs when hydrogen is covalently bonded to fluorine, nitrogen or oxygen
            • These are all very electronegative, so they draw the bonding electrons away from hydrogen.
              • These bonds are so polar that hydrogen can then bond with the lone pair of electrons on another molecule

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