Chemistry Periodic Table - Quick Revision
Chemistry Periodic Table - Quick Revision
Key Points (One-Liners)
- Atomic number = number of protons (defines the element).
- Groups (columns) have 18; Periods (rows) have 7.
- Group 1: Alkali metals (Li, Na, K) – 1 valence e⁻, highly reactive.
- Group 2: Alkaline earth metals (Be, Mg, Ca) – 2 valence e⁻.
- Group 17: Halogens (F, Cl, Br) – 7 valence e⁻, most reactive non-metals.
- Group 18: Noble gases (He, Ne, Ar) – 8 valence e⁻ (octet), inert.
- Atomic size ↓ across period, ↑ down group.
- Metallic character ↑ down group, ↓ across period.
- Valency for groups 1–4 = group number; for 5–7 = 8 – group number.
- Transition metals (d-block) show variable valency & colour.
- Lanthanides & Actinides (f-block) are radioactive & placed separately.
- Mendeleev arranged by atomic mass; Modern table by atomic number.
- Newlands’ Law of Octaves worked only up to Ca (20).
- Dobereiner’s Triads: middle element A.M. ≈ (A.M.1 + A.M.3)/2.
- Electronegativity order: F > O > Cl > N; least: Fr.
- Oxides of metals are basic; of non-metals, acidic.
- Hydrogen placed with both Group 1 & 17 (unique position).
- Zero group was added after discovery of noble gases.
- Maximum elements in 6th period (32) due to filling 4f & 5d.
- Modern table has 118 elements; last is Oganesson (Og, Z=118).
Important Formulas/Rules
| Formula/Rule | Application |
|---|---|
| No. of shells = period number | Locate period of element |
| Valence electrons = units digit of group no. (up to 2 digits) | Predict group & valency |
| Max electrons in shell = 2n² | Check electron capacity |
| Atomic radius ∝ 1 / Effective nuclear charge | Explain size trend |
| Electronegativity difference > 1.7 ⇒ ionic bond | Bond-type prediction |
| (Atomic mass – atomic number) = neutrons | Neutron count |
| Group 1 oxide: M₂O; Group 2: MO | Oxide formula |
| Halogen displacement: Cl₂ + 2KBr → 2KCl + Br₂ | Reactivity series |
| d-block valency = (outer s + unpaired d) electrons | Variable valency |
| Octet rule: 8 e⁻ in outer shell (2 for He) | Stability check |
Memory Tricks
- Group 1 order: LiNa Ki Rb Cse Fry — “Little Naughty Kids Rub Cats Fur”
- Halogens: F Cl Br I At — “First Class Breakfast In Austria”
- Noble gases: He Ne Ar Kr Xe Rn Og — “He Never Arrives; Karen Xenially Runs Out”
- d-block 1st series (21-30): Sc Ti V Cr Mn Fe Co Ni Cu Zn — “Scary Tigers Vanquish Cruel Monkeys, Feasting Comfortably Near Cages.”
- Electronegativity trend: FONCl — “Fancy Old Nuns Climb” (top-right corner).
Common Mistakes
| Mistake | Correct Approach |
|---|---|
| Confusing atomic mass with atomic number | Atomic number = proton count; mass = p⁺ + n⁰ |
| Placing H in fixed group | Remember H is unique; can sit with both 1 & 17 |
| Writing group 12 as 2B (old IUPAC) | Use modern 1-18 numbering |
| Assuming all metals form only basic oxides | Mn, Cr etc. give amphoteric oxides |
| Forgetting 4f/5f make 6th/7th period longer | 6th period = 32 elements (4f=14 + 5d=10 + 6s=6 + 6p=2) |
Last Minute Tips
- Glance at periodic table on last page of question paper first – save 2 min.
- Recall valence e⁻ from group no. – solves 50 % reactivity MCQs instantly.
- Use period for shell count; group for valency – don’t mix.
- Tick “noble gas” if question asks for least reactive element.
- In variable valency Qs, prefer lower oxidation state for bigger atom (e.g., Fe²⁺ > Fe³⁺ size).
Quick Practice (5 MCQs)
1. Which element has the highest electronegativity?
Fluorine (F)
2. An element with atomic number 35 belongs to which period & group?
Period 4, Group 17 (Bromine)
3. The oxide of which element is amphoteric?
Aluminium (Al)
4. Which of the following is a lanthanide?
Cerium (Ce)
5. Atomic size of Li is _____ than Na; True/False: Metallic character increases down a group.
smaller; True
BETA
