Development of Periodic Table and Trends

Study Notes

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 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

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 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.

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.

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.

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.