Covalent Bonding

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Covalent Compounds: bonding and properties

  • formed when 2 atoms share electrons, so each achieves full outer shell - stable
  • strong, holding atoms together, simple molecules like hydrogen, chlorine, oxygen etc
  • bonding within molecules are strong whereas forces of attraction between molecules are weak
  • many covalently bonded simple molecules are gases
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Simple Molecules

  • consist of small number of atoms held together by pairs of electrons, forming covalent bonds
  • covalent bonds join atoms in simple molecules
  • either gases, solids or liquids with relatively low melting and boiling points 
  • don't conduct electricity, no overall electrical charge  
  • elements: hydrogen, oxygen and chlorine
  • compounds: water, hydrogen chloride, methane and ammonia 
  • within is strong, between is weak, when simple molecule either boils or melts, these intermolecular forces that it overcomes 
  • fragrant substances covalently bonded evaporate easily (volatile)
  • in perfumes, substances dissolved in solvents, ethanol, more volatile
  • on skin, solvent evaporates quickly, fragrant molecules evaporate gradually  
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Giant Covalent Structures

  • very strong covalent bonds, join many atoms arranged in 3D Lattice forming macromolecules
  • high melting points, hard don't conduct electricity or dissolve in water
  • diamond and graphite, 2 forms of carbon - giant covalent structures 
  • diamond: covalent bonds join each carbon to 4 others, making  - hardest known natural mineral
  • graphite: each carbon atoms bond to 3 others, forming layers - easily slide over each other, soft and slippery, used as lubricant
  • 1 electron form each carbon atom is delocalised, these electrons enable graphite to conduct electricity and heat
  • silicon dioxide: is silica (sand) strong silicon-oxygen covalent bonds in giant structure, very hard high melting point   
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