📑 Topics on this page (Jump to Topic):
📌 1. History of Classification
| Scientist | Contribution |
|---|---|
| Döbereiner (1829) | Law of triads — Li, Na, K; middle mass ≈ average |
| Newlands (1864) | Law of octaves — every eighth element alike (only up to Ca) |
| Mendeleev (1869) | Properties are periodic functions of atomic mass; 63 elements; left gaps — eka-aluminium (gallium), eka-silicon (germanium) |
| Moseley (1913) | Modern periodic law — properties are periodic functions of atomic number |
📌 2. Modern Periodic Table
- 18 groups (vertical columns) and 7 periods (horizontal rows); 118 elements. Blocks: s, p, d, f.
- Elements in a group have the same outer electrons → similar chemistry. Period number = number of shells.
- Lanthanides (57–71) and actinides (89–103) are placed separately below as the f-block.
| Group | Name | Elements | Feature |
|---|---|---|---|
| 1 | Alkali metals | Li, Na, K, Rb, Cs, Fr | Very reactive, kept in kerosene; release H₂ with water |
| 2 | Alkaline earth metals | Be, Mg, Ca, Sr, Ba, Ra | Valency 2 |
| 3–12 | Transition metals | Fe, Cu, Zn, Ag, Au… | Coloured compounds, catalysts |
| 17 | Halogens | F, Cl, Br, I, At | "Salt formers"; F most electronegative |
| 18 | Noble / inert gases | He, Ne, Ar, Kr, Xe, Rn | Valency 0; complete octet |
📌 3. Periodic Trends & Special Elements
| Property | Across a period (left→right) | Down a group |
|---|---|---|
| Atomic size | Decreases | Increases |
| Metallic character | Decreases | Increases |
| Electronegativity | Increases | Decreases |
| Ionisation energy | Increases | Decreases |
| Feature | Element |
|---|---|
| Lightest / most abundant in universe | Hydrogen |
| Most abundant element / metal in Earth's crust | Oxygen / aluminium |
| Most abundant gas in atmosphere | Nitrogen (~78%) |
| Liquid metal / non-metal at room temperature | Mercury (Hg) / bromine (Br) |
| Most electronegative | Fluorine |
| Heaviest natural / densest metal | Uranium / osmium |
| Highest melting metal | Tungsten |
| First artificial element | Technetium (Tc) |
| Helium first detected in | The Sun's spectrum (1868) |
- Symbols from Latin: Na — Natrium (sodium), K — Kalium (potassium), Fe — Ferrum, Cu — Cuprum, Ag — Argentum, Au — Aurum, Pb — Plumbum, Hg — Hydrargyrum, Sn — Stannum.
- Metalloids: boron, silicon, germanium, arsenic, antimony, tellurium.
⚠️ Exam Traps:
- Mendeleev used atomic mass; Moseley used atomic number.
- The table has 18 groups and 7 periods (not the reverse).
- Potassium's symbol is K, not P (P = phosphorus).
📌 4. Practice MCQs
📝 Practice MCQs (prepared by SF Prep — not PYQs)
Q1. How many groups are there in the modern periodic table? Practice
Correct answer: (B)
18 groups and 7 periods.
18 groups and 7 periods.
Q2. The modern periodic law is based on: Practice
Correct answer: (C)
Given by Moseley (1913).
Given by Moseley (1913).
Q3. Who is called the father of the periodic table? Practice
Correct answer: (B)
He gave the first systematic table in 1869.
He gave the first systematic table in 1869.
Q4. The non-metal that is liquid at room temperature is: Practice
Correct answer: (C)
Mercury is the liquid metal; bromine the liquid non-metal.
Mercury is the liquid metal; bromine the liquid non-metal.
Q5. The most electronegative element is: Practice
Correct answer: (D)
F = 4.0 on the Pauling scale.
F = 4.0 on the Pauling scale.
Q6. The most abundant metal in the Earth's crust is: Practice
Correct answer: (C)
Among elements: oxygen > silicon > aluminium > iron.
Among elements: oxygen > silicon > aluminium > iron.
Q7. Why is sodium stored in kerosene? Practice
Correct answer: (B)
Alkali metals are highly reactive.
Alkali metals are highly reactive.
Q8. Group 18 elements are called: Practice
Correct answer: (C)
They have complete octets.
They have complete octets.
Q9. The chemical symbol of potassium is: Practice
Correct answer: (B)
From Latin "Kalium".
From Latin "Kalium".
Q10. Across a period from left to right, atomic size: Practice
Correct answer: (A)
Increasing nuclear charge pulls electrons closer.
Increasing nuclear charge pulls electrons closer.
Q11. Mendeleev's "eka-aluminium" was later named: Practice
Correct answer: (A)
Discovered in 1875; eka-silicon = germanium.
Discovered in 1875; eka-silicon = germanium.
Q12. Newlands' law of octaves applied only up to: Practice
Correct answer: (B)
It failed for heavier elements.
It failed for heavier elements.
Q13. The first artificially produced element was: Practice
Correct answer: (D)
Made in 1937 (Z = 43).
Made in 1937 (Z = 43).
Q14. The chemical symbol of silver is: Practice
Correct answer: (D)
From Latin "Argentum"; Au = gold.
From Latin "Argentum"; Au = gold.
Q15. Helium was first identified in: Practice
Correct answer: (D)
From a spectral line during the 1868 eclipse; "Helios" = Sun.
From a spectral line during the 1868 eclipse; "Helios" = Sun.
Q16. Which of the following is a metalloid? Practice
Correct answer: (D)
Metalloids show properties of both metals and non-metals.
Metalloids show properties of both metals and non-metals.
Q17. Down a group, metallic character: Practice
Correct answer: (A)
Larger atoms lose electrons more easily.
Larger atoms lose electrons more easily.
Q18. Who gave the law of triads? Practice
Correct answer: (A)
1829; example Li, Na, K.
1829; example Li, Na, K.
Q19. The densest known metal is: Practice
Correct answer: (A)
Osmium ≈ 22.6 g/cm³.
Osmium ≈ 22.6 g/cm³.
Q20. The chemical symbol of lead is: Practice
Correct answer: (C)
From Latin "Plumbum".
From Latin "Plumbum".