Who is called the Father of Modern Chemistry?

Antoine Lavoisier of France is called the Father of Modern Chemistry. He established the law of conservation of mass and named oxygen and hydrogen.

What is the pH of pure water?

Pure water has a pH of 7 — it is neutral. pH below 7 is acidic; pH above 7 is basic (alkaline).

What is the chemical formula of common salt?

Common salt is Sodium Chloride — NaCl. It is formed by the reaction of sodium (Na) and chlorine (Cl₂).

What is the Periodic Table?

The Periodic Table arranges all known elements in order of increasing atomic number. It was developed by Dmitri Mendeleev (1869). The modern periodic table has 118 elements arranged in 18 groups (columns) and 7 periods (rows).

Chemistry Basics — TNPSC Group 4 Science Notes

Overview

Chemistry is the study of matter, its properties, and the changes it undergoes. TNPSC Group 4 chemistry questions focus on school-level concepts — elements, acids and bases, periodic table, common chemical compounds, and everyday chemistry. These questions are straightforward and frequently repeated.

Matter and Its Classification

Matter
├── Pure Substances
│   ├── Elements (only one type of atom) — Gold, Oxygen, Iron
│   └── Compounds (two or more elements, chemically combined) — H₂O, NaCl, CO₂
└── Mixtures (not chemically combined)
    ├── Homogeneous (uniform) — Salt water, air
    └── Heterogeneous (non-uniform) — Sand + water, granite

States of Matter

State	Shape	Volume	Examples
Solid	Fixed	Fixed	Ice, iron, wood
Liquid	Variable	Fixed	Water, mercury, oil
Gas	Variable	Variable	Oxygen, steam, LPG
Plasma	Variable	Variable	Sun's interior, lightning

Atoms and Molecules

Atom — smallest unit of an element that retains its chemical properties
Molecule — smallest unit of a compound or element that can exist independently
Atomic Number = number of protons in nucleus
Mass Number = protons + neutrons

Sub-atomic Particles

Particle	Charge	Location
Proton	Positive (+)	Nucleus
Neutron	Neutral (0)	Nucleus
Electron	Negative (−)	Shells around nucleus

TNPSC Tip: Atomic number of Hydrogen = 1 (simplest element). Carbon = 6. Oxygen = 8. Iron = 26. Gold = 79.

Periodic Table — Key Points

Developed by Dmitri Mendeleev (1869) — arranged elements by atomic mass
Modern table arranged by atomic number (Moseley's contribution)
118 elements known; 94 occur naturally
Groups (vertical columns, 1–18) — elements in same group have similar properties
Periods (horizontal rows, 1–7) — properties change across a period

Key Groups to Remember

Group	Name	Elements	Property
Group 1	Alkali Metals	Li, Na, K	Very reactive, soft metals
Group 2	Alkaline Earth Metals	Mg, Ca	Less reactive than Group 1
Group 17	Halogens	F, Cl, Br, I	Non-metals, very reactive
Group 18	Noble Gases	He, Ne, Ar	Inert — do not react

Important Elements and Symbols

Element	Symbol	Important Use
Hydrogen	H	Lightest element; rocket fuel
Carbon	C	Basis of all organic life
Nitrogen	N	78% of air; fertilizers
Oxygen	O	21% of air; respiration
Iron	Fe	Steel making
Gold	Au	Jewellery, electronics
Silver	Ag	Jewellery, coins
Copper	Cu	Electrical wires
Sodium	Na	Common salt (NaCl)
Calcium	Ca	Bones, teeth
Mercury	Hg	Thermometers

Acids, Bases, and Salts

Acids

Taste sour; turn blue litmus red
pH < 7
Release H⁺ ions in solution

Acid	Formula	Found in
Hydrochloric acid	HCl	Stomach (gastric acid)
Sulphuric acid	H₂SO₄	Car batteries, industrial use
Nitric acid	HNO₃	Fertilizers, explosives
Acetic acid	CH₃COOH	Vinegar
Citric acid	—	Lemon, orange
Formic acid	HCOOH	Ant sting

Bases and Alkalis

Taste bitter, feel soapy; turn red litmus blue
pH > 7
Release OH⁻ ions in solution

Base	Formula	Common Name / Use
Sodium hydroxide	NaOH	Caustic soda — soap making
Calcium hydroxide	Ca(OH)₂	Slaked lime — whitewash
Ammonia	NH₃	Fertilizers, cleaning agents
Magnesium hydroxide	Mg(OH)₂	Milk of magnesia — antacid

Neutralisation

Acid + Base → Salt + Water

Example: HCl + NaOH → NaCl + H₂O

pH Scale

0 ——— 1 ——— 2 ——— 3 ——— 4 ——— 5 ——— 6 ——— 7 ——— 8 ——— 9 ——— 10 ——— 11 ——— 12 ——— 13 ——— 14
|←————————————— Acidic ————————————→| Neutral |←————————————— Basic/Alkaline ————————————→|

TNPSC Tip: Blood pH = 7.35–7.45 (slightly alkaline). Soil pH for crops = 6–7 (slightly acidic to neutral). Baking soda (NaHCO₃) pH ≈ 8.3.

Common Chemical Compounds

Compound	Formula	Common Name	Use
Water	H₂O	—	Universal solvent
Sodium chloride	NaCl	Common salt	Food, preservation
Sodium bicarbonate	NaHCO₃	Baking soda	Cooking, antacid
Calcium carbonate	CaCO₃	Limestone / chalk	Construction, chalk
Carbon dioxide	CO₂	—	Photosynthesis, fire extinguisher
Sulphur dioxide	SO₂	—	Causes acid rain
Nitrous oxide	N₂O	Laughing gas	Anaesthetic
Ozone	O₃	—	UV protection in stratosphere
Hydrogen peroxide	H₂O₂	—	Antiseptic, bleaching
Ammonia	NH₃	—	Fertilizers, refrigerant
Methane	CH₄	Natural gas	Fuel
Chloroform	CHCl₃	—	Anaesthetic

Types of Chemical Reactions

Type	Description	Example
Combination	A + B → AB	2Mg + O₂ → 2MgO
Decomposition	AB → A + B	2H₂O → 2H₂ + O₂
Displacement	A + BC → AC + B	Fe + CuSO₄ → FeSO₄ + Cu
Double Displacement	AB + CD → AD + CB	NaCl + AgNO₃ → AgCl + NaNO₃
Oxidation	Gains oxygen / loses hydrogen	Iron rusting
Reduction	Loses oxygen / gains hydrogen	Opposite of oxidation

Redox reaction — oxidation and reduction always occur together.

Metals vs Non-metals

Property	Metals	Non-metals
State	Mostly solid	Solid, liquid, or gas
Lustre	Shiny	Usually dull
Conductivity	Good conductors	Poor conductors (except graphite)
Malleability	Can be beaten into sheets	Brittle
Examples	Iron, copper, gold, silver	Oxygen, sulphur, carbon

Alloys — Important Ones

Alloy	Composition	Use
Steel	Iron + Carbon	Construction, machinery
Stainless Steel	Iron + Chromium + Nickel	Utensils, surgical tools
Bronze	Copper + Tin	Statues, bells, coins
Brass	Copper + Zinc	Musical instruments, taps
Duralumin	Aluminium + Copper + Mn + Mg	Aircraft body
Solder	Lead + Tin	Electrical connections

Fuels and Their Properties

Fuel	Type	Calorific Value	Key Fact
LPG (Liquefied Petroleum Gas)	Mixture	High	Main component: Butane/Propane; Ethyl mercaptan added for smell
CNG (Compressed Natural Gas)	Methane	High	Cleaner fuel for vehicles
Coal	Solid	Moderate	Non-renewable; major cause of CO₂
Petrol / Diesel	Liquid	High	Non-renewable; engine fuel
Hydrogen	Gas	Very high	Cleanest fuel — produces only water

Previous Year TNPSC Questions (Pattern)

1. Q: pH of pure water is → 7 2. Q: Which acid is present in vinegar? → Acetic acid 3. Q: Laughing gas is → Nitrous oxide (N₂O) 4. Q: Which metal is liquid at room temperature? → Mercury (Hg) 5. Q: Father of Modern Chemistry → Antoine Lavoisier 6. Q: Chemical formula of baking soda → NaHCO₃ 7. Q: Brass is an alloy of → Copper and Zinc

Frequently Asked Questions

An element is a pure substance made of only one type of atom (e.g., gold, oxygen). A compound is formed when two or more elements combine chemically in a fixed ratio (e.g., water H₂O, salt NaCl). A mixture is a combination of substances that are not chemically combined and can be separated by physical methods.