⚡ Periodic Table & Elements: Quick Reference

Instant Access Guide - Definitions, Trends, Properties, Oxidation States & Key Facts

Quick Facts Definitions Reference Tables Cheat Sheet

This quick reference guide provides instant access to essential periodic table information. Perfect for last-minute exam prep, homework help, and quick lookups. Find definitions, trends, element properties, oxidation states, important compounds, and key reactions at a glance.

📖 1. Essential Definitions

Atomic Radius

Definition: Distance from nucleus to valence electron shell

Unit: Å (Angstrom) = 10⁻¹⁰ m or pm (picometer) = 10⁻¹² m

Remember: ↓ Across period | ↑ Down group

Ionization Energy (IE)

Definition: Energy required to remove one electron from gaseous atom → cation

Unit: kJ/mol or eV

Remember: ↑ Across period | ↓ Down group

Electron Affinity (EA)

Definition: Energy released when electron added to gaseous atom → anion

Unit: kJ/mol (negative = energy released)

Remember: ↑ Across period | ↓ Down group

Electronegativity (EN)

Definition: Ability of atom to attract shared electrons in covalent bond

Scale: Pauling scale (0-4); F = 4.0 (highest), I = 2.5

Remember: ↑ Across period | ↓ Down group

Metallic Character

Definition: Tendency of element to form cations and react with nonmetals

Increase: Left to right decreases | Top to bottom increases

Most Metallic: Group 1 (Alkali metals)

Period vs Group

Period: Horizontal row in periodic table (1-7)

Group: Vertical column in periodic table (1-18)

Key: Period number = # electron shells | Group # ∝ valence electrons

📈 2. Periodic Trends at a Glance

↓ ATOMIC RADIUS ↓

Across → (Size ↓)

Down ↑ (Size ↑)

Reason: Nuclear charge ↑ | Shielding ↑

↑ IONIZATION ENERGY ↑

Across → (IE ↑)

Down ↓ (IE ↓)

Reason: Zeff ↑ | Size ↑

↑ ELECTRON AFFINITY ↑

Across → (EA ↑)

Down ↓ (EA ↓)

Reason: Size ↓ | Zeff ↑

↑ ELECTRONEGATIVITY ↑

Across → (EN ↑)

Down ↓ (EN ↓)

Reason: Size ↓ | Zeff ↑

← METALLIC CHARACTER →

Across → (Metal ↓)

Down ↑ (Metal ↑)

Most: Group 1 | Least: Group 17

EXCEPTIONS!

Half-filled & filled d: Cr, Cu

Anomalous: Be, B, C differences

Group 18: Noble gases (inert)

Trend	Across Period	Down Group	Same Period Comparison
Atomic Radius	↓ Decreases	↑ Increases	Na > Mg > Al > Si > P > S > Cl
Ionization Energy	↑ Increases	↓ Decreases	Na < Al < Mg < Si < S < P < Cl
Electronegativity	↑ Increases	↓ Decreases	Li(1.0) < Be(1.5) < B(2.0) < C(2.5) < N(3.0) < O(3.5) < F(4.0)
Metallic Character	↓ Decreases	↑ Increases	Na > Mg > Al > Si (metallic ↓, nonmetallic ↑)

🧩 3. Block-Wise Quick Facts

s-BLOCK

Groups: 1-2

Valence: s¹ or s²

Elements: Li, Na, K / Be, Mg, Ca, Sr, Ba

Oxidation: +1 (G1) | +2 (G2)

Properties: Soft, reactive metals

p-BLOCK

Groups: 13-18

Valence: p¹ to p⁶

Elements: B, Al / C, Si / N, P / O, S / F, Cl / He, Ne, Ar

Oxidation: Variable (±combinations)

Properties: Mixed (metals → nonmetals)

d-BLOCK

Groups: 3-12

Valence: d¹-d¹⁰ + ns¹/²

Elements: Fe, Cu, Zn, Cr, Mn (3d series)

Oxidation: +2 to +7 (variable)

Properties: High density, colored ions, catalytic

f-BLOCK

Groups: Lanthanides (4f) / Actinides (5f)

Valence: f¹-f¹⁴

Elements: Ce-Lu / Th-Lr

Oxidation: Mostly +3

Properties: Similar within series, radioactive (actinides)

⚛️ 4. Important Elements Quick Reference

Group	Elements	Key Element	Oxidation State	Key Property
Group 1	Li, Na, K, Rb, Cs, Fr	Na (most important)	+1	Highly reactive, soft metals
Group 2	Be, Mg, Ca, Sr, Ba, Ra	Ca, Mg	+2	Alkaline earth, reactive
Group 13	B, Al, Ga, In, Tl	Al	+3 (Tl: +1)	Al amphoteric oxide
Group 14	C, Si, Ge, Sn, Pb	C, Si	+4 (+2 for Pb, Sn)	Allotropes (C), network (Si)
Group 15	N, P, As, Sb, Bi	N, P	-3, +3, +5	N limited to NF₃ (no penta)
Group 16	O, S, Se, Te, Po	O, S	-2, +4, +6	SO₂ & SO₄²⁻ most important
Group 17	F, Cl, Br, I, At	Cl	-1 (±others)	F > Cl > Br > I reactivity
d-Block	Fe, Cu, Zn, Cr, Mn	Fe, Cu	+2, +3	Variable states, colored ions

⚗️ 5. Oxidation States Quick Lookup

alkali Metals (Group 1)

Only: +1

Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Fr⁺

Alkaline Earth (G2)

Only: +2

Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺

Aluminum (G13)

Main: +3

Al³⁺ (always)

Fluorine (G17)

Always: -1

F⁻ (no positive state)

Oxygen

Usually: -2

Exception: O₂ (0) | H₂O₂ (-1)

Hydrogen

Usually: +1

Exception: Hydrides (-1)

Nitrogen

States: -3, +3, +5

NH₃ (-3) | NO₂ (+4) | NO₃⁻ (+5)

Sulfur

States: -2, +4, +6

H₂S (-2) | SO₂ (+4) | SO₄²⁻ (+6)

Chromium

Main: +3, +6

Cr(OH)₃ (+3) | K₂CrO₄ (+6)

Manganese

Common: +2, +7

Mn²⁺ | MnO₄⁻ (+7)

Iron

Main: +2, +3

Fe²⁺ (slightly easier)

Copper

Main: +2

Cu⁺ disproportionates in solution

🧪 6. Important Compounds Quick Lookup

NaCl (Rock Salt)

Table salt, PVC, De-icer

NaOH (Caustic Soda)

Neutralization, Saponification

Na₂CO₃ (Soda Ash)

Glass, Detergent production

HCl (Hydrochloric Acid)

Pickling, Metal refining, Stomach acid

Cl₂ (Chlorine Gas)

Bleach, Disinfectant, PVC monomer

H₂SO₄ (Sulphuric Acid)

Fertilizers, Batteries, Metal etching

SO₂ (Sulphur Dioxide)

Reducing agent, Bleach, Food preservative

NH₃ (Ammonia)

Fertilizers, Explosives, Coolant

HNO₃ (Nitric Acid)

Fertilizers, Explosives, Metal etching

H₃PO₄ (Phosphoric Acid)

Fertilizers, Food additive, Buffer

CaCO₃ (Limestone)

Marble, Cement, Antacid, Building

P₄O₁₀ (Phosphorus Pentoxide)

Dehydrating agent, Hygroscopic

💥 7. Key Reactions Quick Guide

Disproportionation

Cl₂ + H₂O ⇌ HCl + HClO

(Cl: 0 → -1, +1)

Element Combustion

S + O₂ → SO₂

P₄ + 5O₂ → P₄O₁₀

Thermal Decomposition

CaCO₃ → CaO + CO₂

(Limestone burning)

Acid-Base

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

Redox (I₂-S₂O₃²⁻)

I₂ + 2S₂O₃²⁻ → 2I⁻ + S₄O₆²⁻

(Common titration)

Halogen Displacement

Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

(F > Cl > Br > I)

⚡ 8. Quick Facts & Memory Aids

🎯 Reactivity Series

Metals: K > Na > Ca > Mg > Al > Zn > Fe > Cu > Hg > Ag

Nonmetals: F > Cl > Br > I

🎯 Most Electronegative

F (4.0) > O (3.4) > N (3.0) > Cl (3.0)

Remember: F is MOST electronegative always

🎯 Ionic Radii

Cations < Neutral atoms < Anions

Na⁺ < Na < Na⁻ (size comparison)

🎯 Diagonal Relationships

Li (NW) ~ Mg: Small, similar size & charge density

Be ~ Al: Amphoteric oxides, covalent compounds

B ~ Si: Covalent, semiconductors

🎯 Inert Pair Effect

Tl: +1 more stable than +3 (Tl⁺ > Tl³⁺)

Pb: +2 more stable than +4 (Pb²⁺ > Pb⁴⁺)

🎯 Anomalies

Cr: [Ar]3d⁵4s¹ (not 3d⁴4s²)

Cu: [Ar]3d¹⁰4s¹ (not 3d⁹4s²)

Pd: [Kr]4d¹⁰ (no 5s electrons)

🎯 Color of Ions

Cu²⁺: Blue | Cr³⁺: Green | MnO₄⁻: Purple

Fe³⁺: Pale yellow | Cr₂O₇²⁻: Orange

🎯 Lanthanide Contraction

f-electrons don't shield well

Zr ≈ Hf (very similar); Ba > La > Lu

🎯 Hydride Stability

Group 17 hydrides: HF > HCl > HBr > HI (stability)

Group 16 hydrides: H₂O > H₂S > H₂Se (stability)

🎯 Oxide Acidity

Across period: Basic → Amphoteric → Acidic

Na₂O (basic) < Al₂O₃ (amphoteric) < CO₂ (acidic)

🎯 Flame Colors

Li: Red | Na: Yellow | K: Violet | Ca: Orange

Cu: Green | Ba: Green | Sr: Crimson

🎯 Halogens NOT in Halide

Halogens form anions only: F⁻, Cl⁻, Br⁻, I⁻

In oxides & oxoacids: positive states +1, +3, +5, +7 (Exception: Fluorine is ALWAYS -1, even in OF₂)

📐 9. Important Formulas & Constants

Effective Nuclear Charge

Z_eff = Z - σ

Z = nuclear charge; σ = shielding

↑ Zeff → smaller radius, higher IE

Electronegativity Difference

ΔEN = |EN(A) - EN(B)|

< 0.4: Nonpolar covalent

0.4-1.7: Polar covalent

> 1.7: Ionic bond

Lattice Energy Trend

Lattice Energy ∝ (Z₁ × Z₂) / (r₁ + r₂)

↑ Charge → ↑ Lattice Energy

↓ Size → ↑ Lattice Energy

Hydration Enthalpy

ΔH_hydration ∝ (Charge²) / (Ionic radius)

Similar pattern to lattice energy

Small highly charged ions: highest hydration

Electronegativity Values

F: 4.0 | O: 3.4 | N: 3.0 | Cl: 3.0

Br: 2.8 | I: 2.5 | C: 2.5 | S: 2.6

Atomic Radii (Approximate)

Li: 152 pm | Na: 186 | K: 227

F: 64 pm | Cl: 99 | Br: 114

🧠 10. Memory Tricks & Mnemonics

Group 1 Reactivity Order

LiNaKRbCsFr: "Little Natalie Keeps Rubies, Cesium Fridge"

Remember: K > Na (as you go down Group 1, reactivity increases)

"NON-metals on Right"

Periodic table: Metals on LEFT, Nonmetals on RIGHT

Remember: Noble Gases in Group 18 (far right)

"Trend Directions"

Across Period: Atomic radius ↓, IE ↑, EN ↑, Metallic ↓

Down Group: Atomic radius ↑, IE ↓, EN ↓, Metallic ↑

"Oxidation States"

Group 1: Always +1 | Group 2: Always +2

O: Usually -2 | H: Usually +1

F: Always -1 (most electronegative)

"DIAGonal Relationships"

DIA: Li↔Mg, Be↔Al, B↔Si

Small, similar charge density → similar chemistry

"NOBLE GASES: INERT"

He, Ne, Ar, Kr, Xe, Rn (Group 18)

Fully filled valence shell → Don't react