Lecture Notes: The Octet Rule in Chemistry

Introduction to Octet Rule

• Atoms seek stability through a full set of valence electrons.
• Stability is achieved by atoms either gaining or losing electrons to reach a complete outer shell.
• The octet rule: Atoms will gain or lose electrons to achieve eight electrons in their outer shell.
• Elements aim to reach the electron configuration of the nearest noble gas.

Understanding the Term "Octet"

• "Octet" refers to a group of eight.
• Examples:
  • Octopus: an animal with eight legs.
  • Octagon: a shape with eight sides.

Structure of an Atom

• Atoms consist of a nucleus and electron shells:
  • Nucleus: Contains protons and neutrons.
  • Electron shells: Contain the electrons.
  • First electron shell: Holds a maximum of 2 electrons.
  • Second electron shell: Holds a maximum of 8 electrons.
  • Third electron shell: Holds a maximum of 8 electrons.
• Valence electrons: Electrons in the outermost shell that determine the properties of the atom.

Examples of Elements and the Octet Rule

• Lithium:
  • Group 1 element.
  • Has 1 valence electron in its outermost shell.
  • Loses 1 electron to achieve the electron configuration of helium.
• Sodium:
  • Also a Group 1 element, similar to lithium.
  • Loses 1 valence electron to achieve the electron configuration of neon.
• Chlorine:
  • Group 17 element.
  • Has 7 valence electrons, needs 1 more to satisfy the octet rule.
  • Gains 1 electron to achieve the electron configuration of argon.

Conclusion

• The octet rule explains atomic stability and reactivity.
• Elements react to achieve an electron configuration similar to noble gases, leading to a full valence shell and stability.