Bonding

Bonding

Ionic
1. Structure
  1. Ionic crystals are giant lattices of ions
    1. "Giant" as made up of many repeating units
2. Properties
  1. Conduct electricity when molten or dissolved
    1. Ions are free to move and carry a charge
  2. High melting points
    1. Strong electrostatic forces need lots of energy to break bonds
  3. Tend to dissolve in water
    1. Polar water molecules pull ions aways from lattice causing it to dissolve
3. Bonding
  1. Strong electrostatic forces of attraction between oppositley charged ions
    1. Electrons transfered between one atom to another forming ions
      1. Not just atons, compounds can form compound ions
        Sulfate SO4 ^2-
        Hydroxide OH-
        Nitrate NO3 ^-
        Carbonate CO3 ^2-
        Ammonium NH4 ^+
        Compounds have overall neutral charge
Covalent
1. Molecules held together by strong covalent bonds
  1. Atoms share electrons to fully saturate both outer shells
    1. Both nuclei attact to shared electrons electrostatically
      1. Double or triple covalent bonds share multiple pairs or electrons
        Covalent bonds shown by 'dash' e.g. C-H
        Covalent bonds don't break during melting or boiling, other than giant covalent substances
        To melt or boil, just overcome the intermolecular forces, dont need break covalent bonds
        Gives simple covalent compounds relatively low melting / boiling points
        So Cl2 is gas at room temp has low MP and BP
        Diamond does need the covalent bonds broken, sublimes at 3600 cel
        MP and BP determined by strength of attraction between particles
    2. Dative covalent bond
      1. Covalent bond in which both electrons come from the same atom
        Shown by an arrow to replace the 'dash' N-->H
2. Giant Covalent structures (Macromolecular)
  1. Many atoms covalently bonded
  2. Diamond
    1. Hardest known substance
      1. Made of carbon, each bonded covalently with 4 other carbon atoms
        Forms a tetrahedral shape with very strong covalent bonds
        High melting point, extremely hard, good thermal conductor
        Cannot conduct electricty (all e- held in bonds), cannot dissolve, refracts light
  3. Graphite
    1. Carbon arranged in sheets of flat hexagons with delocalised e-
      1. Weak bonds between layers causes them to slide in pencils
        Delocalised eletrons can move to carry a charge
        Layers far apart compared to covalent bonds - gives a low density makes strong and lightweight
        Strong covalent bonds in hexagon sheets causes high melting point
        Completely insoluble
    2. one carbon bonded to 3 others
Shape of molecules
1. Shape of a molecule depends on the number or pairs of electrons
  1. Electron pairs exist as charged clouds - there is a high probability of electron pair
    1. As the clouds are all negative they repel each other
      1. Shape affects how much it repels other clouds
        LP:LP strongest repulsion, biggest angles
        LP:BP Strong
        BP:BP Weakest repulsion, smallest angles
        Can work out the shape of molecule using VSEPR
        Find number of electrons on the outer shell of central atom
        Find how many electrons are used in bonding pairs
        Check for charge - positive = less electrons
        Sort any left over electrons as lone pairs
        Shapes
        2 Pairs
        2 BP Linear
        3 Pairs
        3 BP Trigonal Planar
        4 Pairs
        4 BP Tetrahedral
        3BP 1LP Trigonal Pyramidal
        2BP 2LP Bent
        5 Pairs
        5 BP Trigonal Bipyramidal
        4BP 1LP Seesaw
        3BP 2LP T-shaped
        6 Pairs
        6 BP Octahedral
        4BP 2LP Square Planar
Polarisation and Forces
1. Intermolecular forces hold molecules together
  1. Electrogenativity is the ablility of an atom to attact an electron pair
    1. Fluorine, oxygen, chlorine all strongly electronegative
  2. These forces are very weak, weaker than covalent, ionic and metallic bonds
    1. vann der Waals
      1. Perm. Dipole-Dipole
        Hydrogen
        Only happens between FON elements when covalently bonded to hydrogen
        FON very electrogenative, draws BP electrons from H
        As polar bond and Hydrogen high charge density, hydrogen can form bonds with lone pairs on FON atoms
        Increases boiling, melting points. Water, HF higher boiling point in halides cause of h-bonds
        Polar Bonds
        Causing weak electrostatic fordes of attaction between partial charges
      2. Cause all atoms and molecules to attract to each other
        At any moment electrons likely to be on one side of the atom causing a temp. dipole
        This can cause another temp. dipole opposite charged on the next atom, 2 dipoles attracted to each other
        Temp. dipoles constantly created/destroyed overall attraction though
2. Covalent bonds polarised by differences in electronegativity
  1. Covalent bonds between the same element are non-polar as same electronegativity
    1. Water is polar and substances that are polar will dissolved well in it
3. Difference in electronegativity causes polar bond and a permanent dipole
  1. Dipole is a difference in charge between 2 by shift in electron density
Metallic
1. Metals exist in giant metallic lattice structures
  1. Outer most shell of electrons is delocalised
    1. Leaving a positive metal ion that is attracted to d.electrons
      1. Forms a lattice of closely packed positive ions
        In a sea of delocalised electrons (metalic bonding)
        Properties
        High melting points as strong electrostatic attraction between electrons and ions
        More delocalised electrons per atom, stronger bonding, so higher melting point
        D.electrons can pass kinetic energy to each other making them good thermal conductors
        Good electrical conductors as d.electrons can move to carry a current / charge
        Insoluble (except liquid metals)
        Materials (NOT RELATED TO METALLIC)
        Covalent bonds don't break during melting or boiling
        To melt or boil, only break bond between molecules, inter force
        Simple covalent, easy to overcome these forces
        Giant covalent need to break covalent bonds
        thats why it never really melts, only sublimes at 3600 cel

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	Erstellt von Dominic Weston vor mehr als 6 Jahre