Cations and Anions

PlantUML Diagram

3.6 Cations and Anions

Cations

Definition and Formation

Positively charged ions formed when an atom loses one or more electrons.
Usually formed from metal atoms.
Aim to achieve a stable electron configuration similar to noble gases.

Characteristics

Number of protons< Number of electrons, resulting in a positive charge.

Example 3.1: Formation of Cations

  • Na+ formation:
    Na: 1s² 2s² 2p⁶ 3s¹ → Na+: 1s² 2s² 2p⁶
  • Mg2+ formation:
    Mg: 1s² 2s² 2p⁶ 3s² → Mg2+: 1s² 2s² 2p⁶

Problem Solving Strategy for Cation Formation

  1. Identify the element's group in the periodic table.
  2. Determine the number of valence electrons.
  3. Represent the loss of valence electrons using electronic configuration or electron dot structure.

Anions

Definition and Formation

Negatively charged ions formed when an atom gains one or more electrons.
Usually occurs in atoms with high electron affinity.
Aim to achieve a stable electron configuration similar to noble gases.

Characteristics

Number of electrons < Number of protons, resulting in a negative charge.

Example 3.1: Formation of Anions

  • O2- formation:
    O: 1s² 2s² 2p⁴ + 2e⁻ → O2-: 1s² 2s² 2p⁶
  • F- formation:
    F: 1s² 2s² 2p⁵ + e⁻ → F-: 1s² 2s² 2p⁶

Problem Solving Strategy for Anion Formation

  1. Write the electronic configuration or dot structure.
  2. Determine the number of electrons needed to achieve an octet configuration.
  3. Represent the addition of electrons.

Concept Assessment Exercises

  • Exercise 3.2: Describe cation formation for Li and Al.
  • Exercise 3.3: Describe anion formation for S and Cl.