Lesson Plan: Periodic Classification

Inorganic Chemistry

Classification of Elements

This chapter maps the "DNA" of chemistry. Instead of memorizing properties of 118 elements individually, you learn the trends (Radius, Ionization Energy, Electronegativity) that govern them.

📊

⚠️ Prerequisites

Electronic Configuration: You must know how to fill s, p, d, f orbitals (Aufbau principle).
Atomic Structure: Shielding effect and Effective Nuclear Charge ($Z_{eff}$).
Valence Electrons: Identifying the outermost shell.

🧠 Study Approach

Logic over Memory: Do not just memorize "It increases left to right." Ask Why? (Is it due to higher $Z_{eff}$ or added shells?). The exceptions are the most important part of this chapter.

Study Sequence

1. Genesis of Classification

Brief history: Dobereiner's Triads, Newlands' Octaves. Mendeleev's Table (based on Atomic Mass) and its significance.

2. Modern Periodic Law

Based on Atomic Number. Structure of the Long Form Table: Periods (n) and Groups. Classification into s, p, d, f blocks. IUPAC naming for Z > 100.

3. Atomic & Ionic Radius (CRITICAL)

Trend: Decreases L$\to$R, Increases Top$\to$Bottom.
Ionic Radius: Cation < Neutral < Anion.
Isoelectronic Species: Higher atomic number ($Z$) = Smaller radius (Stronger pull).

4. Ionization Enthalpy (IE)

Energy required to remove an electron.
General Trend: Increases L$\to$R, Decreases Down.
Crucial Exceptions: Full/Half-filled stability. ($N > O$ and $Be > B$).

5. Electron Gain Enthalpy (EGE)

Energy released when adding an electron.
The Trap: $Cl$ has the most negative EGE, not $F$ (due to repulsion in small 2p orbital of F).

6. Electronegativity & Valency

Pauling Scale ($F=4.0$, $Cs=0.7$). Metallic vs Non-metallic character. Diagonal Relationships (Li-Mg, Be-Al).

🎯 How to Practice

Reasoning: For every trend question, write the electronic configuration first. Check if the element has a stable (half/full) configuration.

Isoelectronic Series: Arrange these repeatedly: $N^{3-}, O^{2-}, F^-, Na^+, Mg^{2+}, Al^{3+}$. (Hint: Protons pull electrons closer).

Exceptions: Create flashcards for the "Flip" cases: IE of $N > O$, IE of $Be > B$, EGE of $Cl > F$, EGE of $S > O$.

📝 Quick Revision Notes

Atomic Radius

Left $\to$ Right: Decreases (Zeff increases)

Top $\to$ Bottom: Increases (Shells added)

Ionization Enthalpy

Left $\to$ Right: Increases

Exception: Be > B (Full s-orbital)
N > O (Half p-orbital)

Electron Gain Enthalpy (-ve)

Exception: Group 17: Cl > F > Br > I
(F is too small, repels incoming electron)

Highest IE: He

Lowest IE: Cs

Highest EN: F

Highest EGE: Cl

Search This Blog