chap3. Ions & ionic compounds

• Ion


  An atom or a group of atoms with a charge
• Ionization


  Making an ion from an atom or molecule
• Cation


  A positive ion
• Noble gases are elements in Group O or Group 8 (e.g. He, Ne and Ar)
• Noble gases


  • They are unreactive as they have full outer shells
  • They have a stable electron distribution
• Helium


  Has a stable duplet (2 electrons in the outer shell)
• Neon and Argon


  Have a stable octet (8 electrons in the outer shell)
• Noble gases Group O [or Group 8] elements are monatomic - they exist as individual atoms
• Anion


  An ion with a negative charge
• Metallic elements


  • Found mostly in Groups I, II and III
• Metallic atoms


  Have few valence (outer) electrons, tend to lose their valence (outer) electrons to achieve a stable noble gas electron distribution, form cations
• Non-metallic elements


  • Found mostly in Groups IV, V, VI, VII and O
• Non-metallic atoms


  Have many valence (outer) electrons, tend to gain electrons to achieve a stable noble gas electron distribution, form anions
• Group O [or Group 8] elements do not lose or gain electrons as they already have a stable electronic distribution
• Charges of ions in the periodic table

  • Group I: 1+
  • Group II: 2+
  • Group III: 3+
  • Group V: 3-
  • Group VI: 2-
  • Group VII: 1-
• When an atom forms an ion


  The number of electrons changes
• Positive ion (cation)


  Formed when an atom loses electrons
• Negative ion (anion)


  Formed when an atom gains electrons
• Metals form positive ions (cations)
• Non-metals form negative ions (anions)