Formation of Ions

Definition of Ions

• An ion is a charged particle.
  • Single Atom Ion: Example - Na⁺
  • Group of Atoms Ion: Example - OH⁻

How Ions are Formed

• Ions are formed when atoms gain or lose electrons.
• The objective is to achieve a full outer shell, increasing stability.

Role of the Periodic Table

• Group Number: Indicates the number of electrons in the outermost shell of atoms.
  • Group 1: 1 electron
  • Group 2: 2 electrons
  • Continues similarly for other groups.

Stability through Electron Gain/Loss

• Energy Requirement: Losing or gaining electrons requires energy.
• Atoms are more likely to form ions if they need to lose/gain fewer electrons.
  • Group 1 (Alkaline Metals): Lose 1 electron to become 1⁺ ions.
  • Group 2: Lose 2 electrons to become 2⁺ ions.
  • Group 6: Gain 2 electrons to become 2⁻ ions.
  • Group 7: Gain 1 electron to become 1⁻ ions.

Exceptions in Groups

• Elements in Groups 3, 4, and 5 would need to lose or gain 3-4 electrons, requiring too much energy.
• These elements rarely form ions.

Writing Equations for Electron Gain/Loss

• Positive Ion Formation:
  • Example: Sodium (Na → Na⁺ + e⁻)
• Negative Ion Formation:
  • Example: Chlorine (Cl + e⁻ → Cl⁻)
• Multiple Electrons Gained/Lost:
  • Group 2 Example: Magnesium (Mg → Mg²⁺ + 2e⁻)
  • Group 6 Example: Oxygen (O + 2e⁻ → O²⁻)

Conclusion

• Understanding ion formation helps to predict chemical behavior.
• Group numbers and the ease of gaining/losing electrons are key to understanding which atoms tend to form ions.