Chemical bonding

• Noble gas electronic configuration:

  • Noble gases - the last elements in each row of the periodic table. Have full valence electron shells and a noble gas electronic configuration, thus chemically unreactive (inert). Are monotomic, meaning they exist as single atoms.
  • Helium has a duplet electronic configuration while other noble gases have an octet electronic configuration.
• Ion formation - Loss or gain of electrons:

  • Ions are formed when atoms lose or gain electrons to achieve stable duplet or octet noble gas electronic organisation.
  • Positive ions (cations) are formed when an atom loses one or more electrons. Have more protons than electrons and have a net positive charge. E.g. Metal atoms
  • Negative ions (anions) are formed when an atom or combination of atoms gains one or more electrons. Have a net negative charge and usually have a noble gas electronic configuration. E.g. Non-metal atoms
• • Hydrogen is a non-metallic element. The only element that forms anion with no electrons. H+ is just a proton.
  • The ammonium ion is polyatomic. Has more than one atom involved in its combination. Also made from non-metallic elements.

  
• • Fluoride, Chloride, Bromide and Iodide are called 'halide ions', a special name for the anions formed by Group 17 elements.
  • Hydroxide, nitrate, manganate, carbonate, sulfate and phosphate are polyatomic ions.

  
• Ionic bond - the mutual electrostatic attraction between ions of opposite charges.
• Ionic Compounds:

  • a neutral substance made up of ions of opposite charges which are held together by ionic bonds.
  • no net charges because the total positive charges from the positive ions must be equal to the negative charges from the negative ions.
• Ionic Structures - An ionic compound forms a structure called a giant ionic crystal lattice.
• Covalent bond:

  • Valency - the number of electron(s) that must be lost, gained or shared in order for the atom to attain a noble gas electronic configuration.
  • In covalent bonding, electrons are shared so closely that the shells overlap so the bond between the atoms is hard to break.
  • Can occur as long as electrons can be shared between atoms.
• Covalent molecules:

  • Can be made from atoms of the same or different elements
  • Mostly simple molecules
  • Have a countable number of atoms in a fixed ratio
  • Can determine how atoms will bond covalently by comparing the number of electrons each atom shares