Lecture on Periodic Table Trends

Introduction

Trend Down a Group:
- Atomic radius increases as you move down a group.
- Increase in the number of protons (nuclear charge, Z) and electron shells.
- Increased shielding effect due to more inner electron shells.
- Effective nuclear charge decreases, leading to less attraction to valence electrons.
Trend Across a Period:
- Atomic radius decreases from left to right across a period.
- Number of electron shells remains constant.
- Increase in nuclear charge, Z, while shielding effect remains constant.
- Valence electrons experience increased inward attraction, pulling them closer to the nucleus.

Metals:
- Metals lose valence electrons when forming positive ions.
- Example: Sodium atom (Na) becomes smaller as it loses an electron to form Na+.
- Positive ions are smaller than their neutral atoms.
Non-Metals:
- Non-metals gain electrons when forming negative ions.
- Example: Phosphorus (P) gains electrons to become P³⁻, increasing in size.
- Negative ions are larger than their neutral atoms.
- Increased electron repulsion leads to a larger ionic radius.

Trend Down a Group:
- Valence electrons are held more weakly.
- Easier to lose electrons, increasing electropositivity and metallic character.
Trend Across a Period:
- Harder to lose valence electrons across a period due to increased effective nuclear charge.
- Metallic character decreases.

Trend Down a Group:
- Decrease in electronegativity as electropositivity increases (easier to lose electrons).
Trend Across a Period:
- Increase in electronegativity as it becomes harder to lose electrons, making it easier to gain electrons.