ch4 chemical bonding

• the electronic configuration of noble gas is 2 , 8 , 8
• the characteristics of noble gases

  • chemically unreactive
  • monoatomic (exist as single atoms )
  • full valence electron shells
• duplet configuration: 2 electrons in valence shell
• octet configuration: 8 electrons in valence shell
• what diagram is used for showing bonding?

  dot and cross diagram
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  different number of bonds

  A) single

  B) double

  C) triple

  
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  diagram

  A) single

  B) 2

  C) double

  D) 4

  E) triple

  F) 6

  
• delocalised electrons

  outermost electrons lost by metal atoms, they move freely between metal ions
• why do atoms combine?

  achieve a noble gas configuration
• how to achieve a full valence shell?

  lose , gain or share electrons
• cations

  • atoms lose electrons to form cation
  • net positive charge
  • usually metallic atoms
• anions

  • atoms gain electrons to form anion
  • have net negative charge
  • usually non metallic atoms
• ionic bonding definition


  mutual electrostatic attraction between ions of opposite charges
• ionic compounds


  neutral substance consisting of ions of opposite charges held together by ionic bonding. They have no net charge as the total positive and negative charge are equal.
• ionic structures


  In the solid state, they exist as three-dimensional structure of giant ionic crystal lattice
• giant ionic crystal lattice


  alternating positive and negative ions in the ionic structure
• covalent bonding


  bond when two atoms share electrons
• single bond


  share 1 electron each, total 2 electrons are shared
• double bond


  share 2 electrons each, total 4 electrons shared
• triple bond


  share 3 electrons each, total 6 electrons shared
• covalent molecules ( elements )

  Chlorine (Cl2)

  Oxygen (O2)

  Nitrogen (N2)

  Hydrogen (H2)
• covalent molecules: compounds

  Water (H2O)

  Carbon Dioxide (CO2)

  Ammonia (NH3)

  Methane (CH4)
• covalent structures usually are simple molecules or giant molecules


  simple molecules : countable number of atoms in a fixed ratio

  giant molecules: uncountable number of atoms
• simple covalent molecules


  Water and Wax
• Giant covalent molecules


  Diamond and Graphite
• metallic bonding definition


  mutual electrostatic attraction between positively charged ions in a metal and a sea of delocalised electrons
• why metal atoms cannot bond by ionic bonds?

  metal atoms form simple positive ions, not negative ions
• metal atoms are held together by strong electrostatic forces of attraction between the positive metal ions and the delocalised electrons
• during metallic bonding, metal atoms

  • form a giant metallic lattice structure
  • lose their electrons
  • become positively charged ions
• what happens to the electrons which are lost?

  they become delocalised and move freely between metal ions