Development of Periodic Table and Trends

Development of Periodic Table

• Elements in the same group have similar chemical properties, although their physical properties may differ.
• Dmitri Mendeleev and Lothar Meyer independently discovered the periodic law, concluding that elements should be arranged based on their properties.

Periodic Trends

• Periodic trends refer to the patterns observed in the properties of elements across the periodic table.
• Trends include:
  • Effective nuclear charge
  • Atomic and ionic size
  • Ionization energy
  • Electron affinity
  • Metallic character

Effective Nuclear Charge (Zeff)

• In a many-electron atom, electrons are both attracted to the nucleus and repelled by other electrons.
• The effective nuclear charge (Zeff) experienced by an electron is the net positive charge it feels after accounting for shielding effects.
• Zeff increases from left to right across a period due to increasing nuclear charge (protons) and constant shielding.
• Zeff increases from bottom to top within a group due to decreasing principal quantum number (n) and stronger nuclear attraction.

Atomic Size

• Atomic radii tend to increase from right to left across a period due to decreasing Zeff, allowing electrons to occupy larger orbitals.
• Atomic radii increase from top to bottom within a group due to increasing principal quantum number (n), resulting in larger electron shells and orbits.

Sizes of Ions

• Cations are smaller than their parent atoms because the loss of an electron reduces electron-electron repulsions.
• Anions are larger than their parent atoms because the addition of an electron increases electron-electron repulsions.

Isoelectronic Series

• In an isoelectronic series, ions have the same number of electrons but different nuclear charges.
• Ionic size decreases with increasing nuclear charge within an isoelectronic series due to stronger attraction between the nucleus and the electrons.

Bond Length

• Bond length is the distance between two nuclei in a molecule.
• Larger atomic radii lead to longer bond lengths.

Ionization Energy

• Ionization energy is the minimum energy required to remove an electron from the gaseous atom or ion in its ground electronic state.
• First ionization energy refers to the removal of the first electron, while subsequent ionization energies refer to the removal of additional electrons from the ion.