Lecture on the Periodic Table

Introduction to the Periodic Table

• The Periodic Table of the Elements is a fundamental tool in chemistry.
• It appears to be a random arrangement, but it reveals patterns about nature.
• Developed in the mid-1800s, many formats were proposed.
• Dmitri Mendeleev's version was successful due to its data correlation and predictive power.

Structure of the Periodic Table

• Rows are called periods.
• Columns are called groups.
• Elements with similar behavior are grouped together.

Historical Significance

• Mendeleev's table predicted the existence of undiscovered elements.
• Elements in the same group have the same number of valence electrons.
  • Example: Group 1 elements have one valence electron.

Periodic Trends

Atomic Radius

• Increases down a group (adding shells).
• Decreases across a period (increasing nuclear charge).

Ionic Radius

• Electrons repel each other; adding increases size, removing decreases.
• Radii decrease with increasing atomic number for ions with similar electron configurations.

Ionization Energy

• Energy required to remove an electron from an atom.
• Opposite trend to atomic radius:
  • Increases across a period.
  • Decreases down a group.
• Exceptions exist, such as:
  • Oxygen's ionization energy is lower than nitrogen's due to orbital symmetry.
  • Successive ionization energies increase.

Electron Affinity

• Opposite of ionization energy.
• Increases across a period.
• Decreases down a group.
• Exceptions similar to ionization energy.

Electronegativity

• Ability of an atom to attract electrons.
• Increases across a period.
• Decreases down a group.

Conclusion

• Trends to remember: atomic radius, ionization energy, electron affinity, and electronegativity.
• Look forward to learning about chemical bonds in the next lecture.

• Additional Resources: Subscribe for more tutorials and feel free to email with questions.