Chemistry: Periodic Table, Elements, Compounds & Everyday Chemistry for PSC

Chemistry is a reliable 4-8 question block in PSC exams. Most questions test factual recall — element properties, everyday chemistry, acids/bases, and common compounds. This note covers every frequently tested fact.

Periodic Table — Essentials

Fact	Detail
Creator	Dmitri Mendeleev (1869) — arranged by atomic mass; predicted undiscovered elements
Modern table	Based on atomic number (Henry Moseley’s contribution)
Periods	7 horizontal rows
Groups	18 vertical columns
Total elements	118 (as of 2024)
Last element	Oganesson (Og, 118)

Group Names — Must Know

Group	Name	Key Elements
Group 1	Alkali Metals	Li, Na, K, Rb, Cs, Fr
Group 2	Alkaline Earth Metals	Be, Mg, Ca, Sr, Ba, Ra
Group 11	Coinage Metals	Cu, Ag, Au
Group 17	Halogens	F, Cl, Br, I, At
Group 18	Noble/Inert Gases	He, Ne, Ar, Kr, Xe, Rn
Groups 3-12	Transition Metals	Fe, Cu, Zn, Cr, Mn, Co, Ni, etc.
Lanthanides	Rare Earth Elements	La to Lu (atomic numbers 57-71)
Actinides	Radioactive series	Ac to Lr (89-103); includes U, Pu

Important Elements — Quick Reference

Element	Symbol	Atomic No.	Key Fact
Hydrogen	H	1	Lightest element; most abundant in universe; fuel of stars
Helium	He	2	2nd lightest; used in balloons, MRI machines; discovered in Sun’s spectrum first
Carbon	C	6	Basis of organic chemistry; allotropes: diamond, graphite, fullerene, graphene
Nitrogen	N	7	78% of atmosphere; used in fertilizers (Haber process: N₂ + H₂ → NH₃)
Oxygen	O	8	21% of atmosphere; essential for respiration and combustion
Iron	Fe	26	Most used metal; rusting = Fe₂O₃·xH₂O; Earth’s core is mostly iron
Gold	Au	79	Most malleable metal; does not corrode; symbol from Latin “Aurum”
Silver	Ag	47	Best conductor of electricity and heat; “Argentum”
Copper	Cu	29	First metal used by humans; excellent conductor; “Cuprum”
Mercury	Hg	80	Only metal liquid at room temperature; used in thermometers; “Hydrargyrum”
Tungsten	W	74	Highest melting point (3,422°C); used in bulb filaments; “Wolfram”
Uranium	U	92	Nuclear fuel; radioactive; discovered by Martin Klaproth
Radium	Ra	88	Discovered by Marie Curie and Pierre Curie; radioactive
Platinum	Pt	78	Used in catalytic converters, jewellery

Allotropes

Element	Allotropes
Carbon	Diamond (hardest natural substance), Graphite (soft, conductor), Fullerene (C₆₀, Buckminsterfullerene), Graphene
Oxygen	O₂ (oxygen), O₃ (ozone)
Phosphorus	White (poisonous, glows), Red (used in matchsticks), Black
Sulphur	Rhombic, Monoclinic

Acids, Bases and Salts

Common Acids

Acid	Formula	Common Name/Use
Hydrochloric acid	HCl	Muriatic acid; in stomach (gastric juice)
Sulphuric acid	H₂SO₄	”King of Chemicals”; battery acid; most produced industrial chemical
Nitric acid	HNO₃	Aqua fortis; used in fertilizers, explosives
Acetic acid	CH₃COOH	Found in vinegar (4-8% solution)
Citric acid	C₆H₈O₇	Found in citrus fruits (lemon, orange)
Carbonic acid	H₂CO₃	Found in soft drinks/soda water
Formic acid	HCOOH	Found in ant stings; simplest carboxylic acid
Oxalic acid	C₂H₂O₄	Found in tomatoes, spinach
Tartaric acid	C₄H₆O₆	Found in grapes, tamarind
Lactic acid	C₃H₆O₃	Produced during muscle fatigue; found in curd
Aqua Regia	HCl + HNO₃ (3:1)	Dissolves gold and platinum

Common Bases

Base	Formula	Use
Sodium hydroxide	NaOH	Caustic soda; soap making
Potassium hydroxide	KOH	Caustic potash; soft soap
Calcium hydroxide	Ca(OH)₂	Slaked lime; whitewashing
Magnesium hydroxide	Mg(OH)₂	Milk of magnesia; antacid
Ammonium hydroxide	NH₄OH	Cleaning agent

pH Scale

pH	Nature	Examples
0-6.9	Acidic	Lemon juice (~2), Vinegar (~3), Coffee (~5)
7	Neutral	Pure water
7.1-14	Basic/Alkaline	Blood (~7.4), Seawater (~8), Soap (~9-10), NaOH (~14)

Indicators: Litmus: red in acid, blue in base. Phenolphthalein: colourless in acid, pink in base. Methyl orange: red in acid, yellow in base.

Important Compounds

Compound	Formula	Common Name
Sodium chloride	NaCl	Common salt / Table salt
Calcium carbonate	CaCO₃	Limestone, marble, chalk
Sodium bicarbonate	NaHCO₃	Baking soda
Sodium carbonate	Na₂CO₃	Washing soda
Calcium oxide	CaO	Quick lime
Calcium hydroxide	Ca(OH)₂	Slaked lime
Calcium sulphate hemihydrate	CaSO₄·½H₂O	Plaster of Paris (POP)
Calcium sulphate dihydrate	CaSO₄·2H₂O	Gypsum
Sodium hypochlorite	NaOCl	Bleaching agent
Potassium nitrate	KNO₃	Saltpetre; gunpowder ingredient
Copper sulphate	CuSO₄·5H₂O	Blue vitriol
Iron sulphate	FeSO₄·7H₂O	Green vitriol
Zinc sulphate	ZnSO₄·7H₂O	White vitriol

Everyday Chemistry — PSC Favourites

Question	Answer
Tear gas chemical?	Chloroacetophenone or CN gas
Laughing gas?	Nitrous oxide (N₂O)
Marsh gas?	Methane (CH₄)
Dry ice?	Solid CO₂
Heavy water?	D₂O (Deuterium oxide)
Hardest natural substance?	Diamond
Softest mineral?	Talc (Mohs scale = 1)
Rust?	Hydrated iron oxide (Fe₂O₃·xH₂O)
Baking powder?	NaHCO₃ + cream of tartar (acid)
Bleaching powder?	Ca(OCl)Cl — Calcium oxychloride (calcium hypochlorite mixture)
LPG gas?	Butane + Propane mixture
CNG?	Compressed Natural Gas (mainly methane)
Ethanol added to LPG for smell?	No — Ethyl mercaptan (thiol) is added for odour detection
Rusting prevention?	Galvanization (zinc coating), painting, oiling

Metals and Non-Metals

Property	Metals	Non-Metals
State	Mostly solid (exception: Mercury = liquid)	Solid, liquid (Bromine), gas
Conductivity	Good conductors	Poor conductors (exception: Graphite)
Malleability	Malleable and ductile	Brittle
Lustre	Shiny	Dull
Oxide	Basic	Acidic

Metallurgy Quick Facts

Ore	Metal	Process
Bauxite	Aluminium	Bayer process + Hall-Heroult electrolysis
Haematite	Iron	Blast furnace
Galena	Lead	Roasting
Cinnabar	Mercury	Roasting
Chalcopyrite	Copper	Smelting

Quick Recall

1. Father of Periodic Table? → Mendeleev
2. Aqua Regia ratio? → 3 HCl : 1 HNO₃
3. King of Chemicals? → H₂SO₄ (Sulphuric acid)
4. Baking soda formula? → NaHCO₃
5. Laughing gas? → N₂O
6. Only liquid metal? → Mercury
7. Highest melting point metal? → Tungsten
8. Blue vitriol? → CuSO₄
9. Plaster of Paris? → CaSO₄·½H₂O
10. pH of blood? → ~7.4