2.1 Formation of Ions

• What is an ion?

  An ion is a charged particle.
• How are ions formed?

  Ions are formed when atoms gain or lose electrons.
• Why do atoms form ions?

  Atoms form ions to have a full outer shell and become more stable.
• What does the group number in the periodic table indicate?

  The group number indicates how many electrons are in the outermost shell of the atoms.
• How many electrons do group one elements have in their outermost shell?

  Group one elements have one electron in their outermost shell.
• How many electrons do group two elements have in their outermost shell?

  Group two elements have two electrons in their outermost shell.
• Why are group one and group two elements more likely to form ions?

  They are more likely to form ions because they only need to lose or gain one or two electrons, which requires less energy.
• What type of ions do group one elements form?

  Group one elements form one plus ions.
• What type of ions do group two elements form?

  Group two elements form two plus ions.
• What type of ions do group six elements form?

  Group six elements gain two electrons to become two minus ions.
• What type of ions do group seven elements form?

  Group seven elements gain one electron to become one minus ions.
• Why do elements in groups three, four, and five rarely form ions?

  They rarely form ions because they would have to lose or gain three or four electrons, which requires a lot of energy.
• How can we represent the gain or loss of electrons in chemical equations?

  • Sodium atom forms a sodium ion:
  • \( \text{Na} \rightarrow \text{Na}^+ + e^- \)
  • Chlorine atom forms a chloride ion:
  • \( \text{Cl} + e^- \rightarrow \text{Cl}^- \)
• How do we represent the formation of a magnesium ion?

  We write \( \text{Mg} \rightarrow \text{Mg}^{2+} + 2e^- \).
• How do we represent the formation of an oxygen ion?

  We write \( \text{O} + 2e^- \rightarrow \text{O}^{2-} \).
• What is the general trend for elements in groups one and two regarding ion formation?

  • Group one: Lose one electron to form one plus ions.
  • Group two: Lose two electrons to form two plus ions.
  • Group six: Gain two electrons to form two minus ions.
  • Group seven: Gain one electron to form one minus ions.