Periodic Vault · Classification & Trends | Complete Study Guide

Periodic Table Mastery

Classification · Laws · Electronic Configuration · Trends & Smart Tricks

1. Classification of Elements | Periodic Laws

Classification of elements is the arrangement of elements based on their properties, leading to the modern periodic table. Elements are grouped to reveal repeating (periodic) trends.

Mendeleev’s Periodic Law (1869)

“Properties of elements are a periodic function of their atomic masses.” Mendeleev arranged 63 elements in order of increasing atomic mass & left gaps for undiscovered elements.
Limitations Anomalies like Ar (39.9) before K (39.1) & isotopes issue.

🔁 Short Trick: “Maasive Law” – Mendeleev = Mass based. Later Modern = Atomic number based.

Modern Periodic Law (Moseley, 1913)

“Properties of elements are a periodic function of their atomic number (Z).” Removed all anomalies & provided a scientific basis. Modern table arranges elements by increasing Z → strict periodicity.

💡 Mnemonic: Zoo Periodic – Z (atomic number) is the real hero!

✅ Why Modern law wins: Atomic number is unique, explains isotopes same Z, and gives perfect periodicity. The modern periodic table has 7 periods & 18 groups.

2. Electronic Configuration up to Atomic Number 20

Definition: Distribution of electrons in atomic orbitals (K, L, M, N shells) following Aufbau principle, Pauli exclusion, Hund’s rule. Order of filling: 1s → 2s → 2p → 3s → 3p → 4s (since 4s is lower in energy than 3d up to Z=20).

✨ Diagonal rule / Aufbau memory trick: “1s 2s 2p 3s 3p 4s” → just remember: Smart Students Play Smartly, Then Proceed to 4s
✅ Electron configuration formula: Max electrons per orbital: s², p⁶, d¹⁰… For first 20 elements, we stop at 4s² (Calcium).

Atomic No.	Element	Symbol	Electronic Configuration (full / abbreviated)
1	Hydrogen	H	1s¹
2	Helium	He	1s²
3	Lithium	Li	[He] 2s¹
4	Beryllium	Be	[He] 2s²
5	Boron	B	[He] 2s² 2p¹
6	Carbon	C	[He] 2s² 2p²
7	Nitrogen	N	[He] 2s² 2p³
8	Oxygen	O	[He] 2s² 2p⁴
9	Fluorine	F	[He] 2s² 2p⁵
10	Neon	Ne	[He] 2s² 2p⁶
11	Sodium	Na	[Ne] 3s¹
12	Magnesium	Mg	[Ne] 3s²
13	Aluminium	Al	[Ne] 3s² 3p¹
14	Silicon	Si	[Ne] 3s² 3p²
15	Phosphorus	P	[Ne] 3s² 3p³
16	Sulfur	S	[Ne] 3s² 3p⁴
17	Chlorine	Cl	[Ne] 3s² 3p⁵
18	Argon	Ar	[Ne] 3s² 3p⁶
19	Potassium	K	[Ar] 4s¹
20	Calcium	Ca	[Ar] 4s²

🎯 Super short trick for 1–20: “He Heals But Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca” – and config: last electron enters s or p orbital.
✅ Formula check: K (19) = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹, Ca (20) = adds one more 4s².

3. Modern Periodic Table: Groups, Periods & Blocks

The modern table has 18 groups (vertical columns) and 7 periods (horizontal rows). Elements are grouped into 4 blocks (s, p, d, f) based on the subshell where the last electron enters.

📌 s-block Groups 1 & 2 + He (group 18) – last e⁻ in s-orbital. Alkali & alkaline earth metals.

📌 p-block Groups 13 to 18 (except He) – last e⁻ in p-orbital. Includes metals, non-metals, metalloids.

📌 d-block Groups 3 to 12 – transition metals, last e⁻ in d-orbital.

📌 f-block Lanthanides & Actinides – last e⁻ in f-orbital (inner transition).

⏱️ Periods: Period 1 (2 elements), Period 2 & 3 (8 elements each), Period 4 & 5 (18 elements), Period 6 (32), Period 7 (incomplete). Elements in same group share similar valence configuration → similar chemical properties.

🔁 Memory trick for blocks: “simple metals, poor metals & nonmetals, delicious transition, fantastic inner transition”.

4. Metals, Non‑metals, Metalloids & Core Periodic Trends

Metals, Nonmetals & Metalloids

🔹 Metals (left & centre): high conductivity, malleable, ductile, lose e⁻ → cations. Ex: Na, Mg, Fe.
🔹 Non‑metals (right side): poor conductors, gain e⁻ → anions. Ex: O, Cl, S.
🔹 Metalloids (staircase): B, Si, Ge, As, Sb, Te – semiconducting properties.

🎯 Mnemonic for metalloids: “Beautiful Silicon Ge As Sb Te” – the semi-metal gang.

Atomic Size (Atomic Radius)

Definition: Half the distance between nuclei of two identical atoms bonded together. Trends: ✔️ Across a period (left→right) → decreases due to increased nuclear charge pulling electrons inward. ✔️ Down a group → increases due to addition of new shells.

Short trick: “PeRiodic DECREASE” (across) & “Group GROW” (down). Largest atom = Fr, smallest = He (among stable).

Electronegativity (χ)

Definition: Ability of an atom to attract shared electrons in a covalent bond. Pauling scale (0.7–4.0). Formula hint: Mulliken electronegativity: χ = (IE + EA)/2 (in eV).
Trend: Increases across period (left→right), decreases down group. Most electronegative = Fluorine (4.0).

🔥 Trick to remember order (F > O > N > Cl): “FONCl – Fluorine Oxygens Neon? Actually Fluorine #1: Friendly Otter Never Claws”. Across period 2: Li→F electronegativity rises.

Valency & Reactivity

Valency: Combining capacity of an element = number of electrons lost, gained or shared to achieve octet. For main group: valency = group number (1,2) or (8–group number) for groups 13-18.
Reactivity trends: ✔️ Metals (group 1) reactivity increases down group (larger size → easier e⁻ loss). ✔️ Non‑metals (halogens) reactivity decreases down group (F₂ most reactive). ✔️ Across period: reactivity of metals decreases, non‑metals reactivity increases.

⚡ Valency trick
Group 1 → +1, Group 2 → +2, Group 17 → -1, Group 16 → -2.

🧪 Reactivity mnemonic
“LiNa K Rb Cs Fr – Little Naughty Kids Rub Cats Frantically” (reactivity ↑). Halogens: “F Cl Br I At – reactivity ↓”.

5. Quick Reference: Definitions, Formulas & Pro Tricks

📖 DEFINITIONS:

Periodic property: Property that repeats at regular intervals in the periodic table.
Ionization energy (IE): Energy required to remove most loosely bound e⁻ from an isolated atom.
Electron affinity (EA): Energy released when an atom gains an e⁻.
Atomic radius: van der Waals / covalent radius.

⚙️ IMPORTANT FORMULAS:
➤ Mulliken electronegativity: χ = (IE + EA) / 2 (in eV units).
➤ Effective nuclear charge (Slater’s approx): Z_eff = Z – σ
➤ Valence electrons: Group number for main group elements.

💎 SUPER SHORT TRICKS for EXAMS:
✅ Atomic size order down group: “Fr > Cs > Rb > K > Na > Li” (Fruits Come Really Keeping Nice Lemon).
✅ Electronegativity decreasing order: F > O > N > Cl > Br > I > S > C > P > H. Trick: “FONCl BrISCPH” – pronounce “fonkel brisc ph”.
✅ Metallic character: decreases across period, increases down group (opposite of non‑metallic).
✅ Melting point trend across period 3: Na, Mg, Al (↑) then Si (high), P, S, Cl, Ar (low).

Electronic Configuration Mnemonics (1 to 20)

Aufbau sequence: 1s² → 2s² 2p⁶ → 3s² 3p⁶ → 4s² → 3d¹⁰… For first 20, after 4s² (Ca). Mnemonic: “Some People Play, Some People Play, 4s²!”

📘 BLOCK-WISE VALENCY TRICK:
s-block: valency = group no. ; p-block: valency = group no. – 10 (13→3, 14→4, 15→3,5, 16→2, 17→1, 18→0).
Reactivity series of metals (short): K > Na > Ca > Mg > Al > Zn > Fe > Sn > Pb > H > Cu > Ag > Au.

6. One‑Glance Trends & Comparison Table

Property	Across Period (→)	Down Group (↓)	Short trick / Formula
Atomic radius	Decreases	Increases	Z_eff increases across → radius shrinks
Electronegativity	Increases (F max)	Decreases	χ = (IE+EA)/2 (Mulliken)
Ionization energy	Increases	Decreases	IE trend matches electronegativity
Metallic character	Decreases	Increases	Fr = most metallic, F = most non‑metallic
Reactivity (metals)	Decreases	Increases	group 1: Li→Fr reactivity ↑
Reactivity (nonmetals)	Increases (halogens)	Decreases	F₂ most reactive halogen

💬 Final mnemonic for periodic trends: “Atomic radius & Metallic character go DOWN the group; Electronegativity, IE go UP the group & rightwards.”

✨ Bonus concept: Periodicity arises due to similar valence shell electronic configuration after regular intervals. This is why group 1 (ns¹) all form +1 ions, group 17 (ns² np⁵) form –1 ions.

classification of element c