Structure and Bonding

Atomic Structure
1. The atomic number and Mass number describe different features of an atom.
2. Relative atomic masses
3. An isotope is: ' A different atomic form of the same element, with the same number of protons and electrons, but a different number of neutrons.
  1. same atomic number- different mass number
Ionic Bonding
1. Transferring Electrons
2. Atoms lose or gain electrons to form charged particles (ions)- strongly attracted to each other
  1. Group 1 and 2 metals only have to lose one/two electrons to become stable ions (+ charge)
  2. Elements in Groups 6 and 7 only have to gain one/two electrons to become stable ions (- charge)
    1. Latch onto atoms that the gave/gained electron from
3. Regular Giant Ionic Lattices
  1. Very Strong electrostatic forces of attraction between oppositely charged ions in all directions
4. Properties
  1. High melting and boiling points- strong attraction between ions
  2. When molten, ions are free to move- will carry electric current
  3. Dissolve easily in water. Ions separate- free to move- carry electric current
5. Ions and Formulas
  1. Ions have the structure of a noble gas
  2. Groups 1,2,6 and 7 most readily form ions.
  3. Group 1 and 2 elements = metals - form + ions Group 1 elements( alkali metals) form ions with non metals where metal has 1+ charge
  4. Group 6 and 7 elements = non-metals- gain electrons to form - ions Group 7 elements (halogens) form ionic compound with alkali metals where halide ion has 1- charge
  5. Charge on positive ions is the same as group number e.g. Group 1 + LI+ Group 7 = F-
  6. Charges must balance each other e.g. MgCl2
Covalent Bonding
1. Sharing electrons
2. Covalent Bond = shared pair of electrons
3. Dot and Cross diagrams
4. Simple Molecular Substances
  1. Very strong covalent bonds to form small molecules of several atoms.
  2. Intermolecular forces = very weak - Melting and boiling points are very lows - molecules easily parted
  3. Most molecular substances are gases/ liquids at room temperature but can be solids
  4. Don't conduct electricity - no ions, no electrical charge
5. Giant Covalent (Macromolecules)
  1. Similar to giant ionic lattices except no charged ions
  2. All atoms bonded to each other by strong covalent bonds- very high melting/boiling points
  3. Don't conduct electricity- except graphite
  4. Main examples = Diamond and Graphite
    1. Diamond- Each carbon atom forms four covalent bonds in a v. rigid giant covalent structure. Diamond = hardest natural substance -used for drill tips
    2. Graphite- Each carbon atom has 3 covalent bonds. Creates layers- free to slide over each other. Graphite soft and slippery. Layers can be rubbed off onto paper e.g. a pencil. Weak intermolecular forces between layers. Only non-metal that's a good conductor of heat and electricity. Delocalised electrons that conduct heat and electricity
Metallic Structures
1. Giant Structure
2. Metallic bonds involve 'free electrons'- come from outer shell of the metal atoms and produce the properties of metals
3. Electrons free to move- good conductors of heat and electricity
4. These electrons hold atom together in regular structure- strong forces of electrostatic attraction between + metal atoms and - electrons
5. Electrons allow layers of atoms to slide over each other - metals can be bent/shaped
6. Alloys
  1. Harder than pure metals-different sized atoms distorting layers- more difficult to slide over each other = harder
New Materials
1. Smart Materials
  1. Behave differently depending on conditions e.g. temperature
  2. Nitinol = shape memory alloy- when cool bends and twist like rubber. When heatedit goes back to a 'remembered' shape- used for braces
2. Nanoparticles
  1. Between 1-100 nanometres across 1nm=0.000000001m
  2. Contain roughly a few hundred atoms
  3. Include fullerenes- molecules of carbon, shaped like hollow balls or closed tubes- arranged in hexagonal rings. Different fullerenes have different numbers of carbon atoms
  4. A nanoparticle has v. different properties from the bulk chemical e.g. fullerenes have different properties from big lumps of carbon
  5. Fullerens can be joined together to make nanotubes. All the covalent bonds make nanotubes v. strong- Can be used to reinforce graphite in tennis rackets
  6. Nanoscience
    1. Huge surface area to volume ratio- could help make new catalysts
    2. Nanotubes can make stronger, lighter building materials
    3. Sun cream can include nanoparticles- do't leave white marks
    4. Nanomedicine- fullerenes absorbed more easily by the body - could deliver drugs into the cells where they're needed
    5. Nanotubes conduct electricity

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