Lecture on the Periodic Table

Introduction

• The periodic table is a widely recognized tool in chemistry.
• Initially, it may appear as a random arrangement of elements.
• Arranged to reveal patterns and principles of nature.

History and Development

• Dmitri Mendeleev: Created the modern periodic table format.
  • Arranged elements into rows (periods) and columns (groups).
  • Grouped elements with similar behaviors.
  • Predicted existence and properties of undiscovered elements through gaps.

Understanding Element Groups

• Elements in the same group have the same number of valence electrons.
  • Group 1: One valence electron (e.g., Alkali metals).
  • Group 2: Two valence electrons (e.g., Alkaline earth metals).
  • Determines many chemical characteristics.

Periodic Trends

1. Atomic Radius
   • Increases down a group (more shells are added).
   • Decreases across a period (increased nuclear charge pulls electrons closer).
2. Ionic Radius
   • Addition of electrons increases size due to repulsion.
   • Removal of electrons decreases size.
3. Ionization Energy
   • Energy required to remove an electron.
   • Decreases down a group (electrons farther from nucleus).
   • Increases across a period (stronger nuclear attraction).
   • Elements like francium are easily ionized; helium is not.
   • Successive ionization energies increase due to instability when removing more electrons.
   • Exceptions explained by orbital symmetry (e.g., oxygen vs. nitrogen).
4. Electron Affinity
   • Opposite of ionization energy; how much an atom wants to gain an electron.
   • Increases across a period (excluding noble gases).
   • Elements like fluorine have high electron affinity (achieve full shell).
5. Electronegativity
   • Ability of an atom to hold electrons tightly.
   • Increases across a period (smaller atoms with more protons).
   • Important for understanding chemical bonds.

Conclusion

• Remember trends: Atomic radius, ionization energy, electron affinity, and electronegativity.
• Upcoming topics: Chemical bonds.
• Encouragement to subscribe and further contact for questions.