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Atoms, Elements and Compounds, Structure of Matter, Bonding, Atomic…

- - - - Radioactive isotopes (radioisotopes) are unstable due to the imbalance of neutrons and protons
      - this causes the nucleus to decay over time through nuclear fission and emit radiation.
      - eg. - tritium and carbon-14
      - decay occurs at a different rate for each isotope
      - the time taken for the radioactivity of an isotope to decrease by 50% is constant for that particular isotope and is known as the half-life
      - Medical uses
        
        radioactivity kills cells so isotopes are used to treat cancer
        
        isotope can be injected into the blood and its path through the body traced with a radioactive detecting camera, revealing the flow of blood through bodily systems
        
        Medical instruments and materials are routinely sterilized by exposure to radiation, which kills any bacteria present
      - Industrial Uses
        
        Radioactive dating uses the carbon-14 isotope to date carbon-containing materials such as organic matter, rocks and other artifacts
        
        The half-life of C-14 is 5730 years and so this technique is often used to date very old historical objects
        
        radioactive tracers are deployed to detect leaks in gas or oil pipes
        
        The radioactive isotope uranium-235 is used as nuclear in power plants in controlled fission reactions
    - - Non-radioactive isotopes are stable atoms which really only differ in their mass
- - - - Each carbon atom bonds with four other carbons, forming a tetrahedron
      - All the covalent bonds are identical and strong with no weak intermolecular forces
      - Does not conduct electricity
      - Has a very high melting point
      - Is extremely hard and dense
      - Diamond is used in jewellery and as cutting tools
      - The cutting edges of discs used to cut bricks and concrete are tipped with diamonds
      - Heavy-duty drill bits and tooling equipment are also diamond-tipped
  - - - Each carbon atom is bonded to three others forming layers of hexagonal-shaped forms, leaving one free electron per carbon atom
      - These free electrons exist in between the layers and are free to move and carry charge, hence graphite can conduct electricity
      - The covalent bonds within the layers are very strong but the layers are connected to each other by weak intermolecular forces only, hence the layers can slide over each other making graphite slippery and smooth
      - Conducts electricity
      - Has a very high melting point
      - Is soft and slippery, less dense than diamond (2.25 g/cm3)
      - Graphite is used in pencils and as an industrial lubricant, in engines and in locks
      - It is also used to make non-reactive electrodes for electrolysis
      - Extended Only
  - - - macromolecular compound which occurs naturally as sand
      - Each oxygen atom forms covalent bonds with 2 silicon atoms and each silicon atom in turn forms covalent bonds with 4 oxygen atoms
      - A tetrahedron is formed with one silicon atom and four oxygen atoms, similar as in diamond