Chemistry Notes for SSC, Railway & Competitive Exams
Chemistry is an important part of General Science for SSC, Railway, Banking, Defence, Police and other competitive examinations. These notes explain the basic concepts of Chemistry in simple English with important facts, formulas and revision points for quick learning.
Introduction
Chemistry is the branch of science that studies the composition, structure, properties and changes of matter. It helps us understand everything from the air we breathe and the food we eat to medicines, fuels and industrial products.
Questions from Chemistry are frequently asked in SSC, Railway, Defence, Banking, Police and State Government examinations. Most questions are based on matter, atoms, elements, compounds, acids, bases, salts and the periodic table.
- Matter
- Atoms & Molecules
- Elements & Compounds
- Periodic Table
- Acids, Bases & Salts
- Chemical Reactions
- Metals & Non-Metals
- Important Compounds
Matter
Matter is anything that has mass and occupies space. Everything around us, including air, water, rocks and living organisms, is made of matter.
States of Matter
| State | Main Characteristics |
|---|---|
| Solid | Fixed shape and fixed volume. |
| Liquid | Fixed volume but no fixed shape. |
| Gas | No fixed shape or fixed volume. |
- Solids have the strongest intermolecular forces.
- Gases have the weakest intermolecular forces.
- Particles of matter are always in motion.
Quick Revision
- Solid → Fixed Shape & Volume
- Liquid → Fixed Volume
- Gas → No Fixed Shape & Volume
Physical and Chemical Changes
Changes in matter are classified into physical changes and chemical changes.
| Physical Change | Chemical Change |
|---|---|
| No new substance is formed. | New substance is formed. |
| Usually reversible. | Usually irreversible. |
| Example: Melting of ice. | Example: Rusting of iron. |
Quick Revision
- Melting → Physical Change
- Rusting → Chemical Change
- Burning → Chemical Change
Elements, Compounds and Mixtures
| Term | Definition |
|---|---|
| Element | Pure substance made of only one type of atom. |
| Compound | Two or more elements chemically combined in a fixed ratio. |
| Mixture | Two or more substances physically mixed in any proportion. |
- Element → Oxygen, Iron, Gold
- Compound → Water (H₂O), Carbon Dioxide (CO₂)
- Mixture → Air, Salt Solution
Compound → Chemical Combination
Mixture → Physical Combination
Atoms and Molecules
An atom is the smallest particle of an element that retains its chemical properties. A molecule is formed when two or more atoms combine chemically.
| Term | Description |
|---|---|
| Atom | Smallest unit of an element. |
| Molecule | Group of atoms chemically bonded together. |
- Hydrogen is the lightest element.
- Oxygen molecule contains two oxygen atoms (O₂).
- Water molecule contains two hydrogen atoms and one oxygen atom (H₂O).
Quick Revision
- Atom → Smallest Particle
- Molecule → Group of Atoms
- Water → H₂O
- Oxygen → O₂
Atomic Structure
Every atom consists of three main subatomic particles: electrons, protons and neutrons. Protons and neutrons are present in the nucleus, while electrons revolve around the nucleus in shells.
| Particle | Charge | Location |
|---|---|---|
| Electron | Negative (−) | Outside the nucleus |
| Proton | Positive (+) | Inside the nucleus |
| Neutron | No charge | Inside the nucleus |
- Electron was discovered by J. J. Thomson.
- Proton was discovered by Ernest Rutherford.
- Neutron was discovered by James Chadwick.
- The nucleus contains almost all the mass of an atom.
📘 Remember
Atomic Number = Number of ProtonsMass Number = Protons + Neutrons
Quick Revision
- Electron → Negative
- Proton → Positive
- Neutron → Neutral
- Atomic Number → Protons
Periodic Table
The Periodic Table is the systematic arrangement of chemical elements based on their atomic number. The modern periodic table was developed by Henry Moseley, while the first widely accepted periodic table was proposed by Dmitri Mendeleev.
- Modern Periodic Table
- Groups & Periods
- Mendeleev
- Henry Moseley
| Feature | Information |
|---|---|
| Total Groups | 18 |
| Total Periods | 7 |
| Basis of Modern Table | Atomic Number |
| Father of Periodic Table | Dmitri Mendeleev |
- Elements in the same group have similar chemical properties.
- Atomic number increases from left to right.
- The modern periodic table is arranged according to increasing atomic number.
Quick Revision
- Groups → 18
- Periods → 7
- Modern Table → Henry Moseley
- Periodic Table → Mendeleev
Metals and Non-Metals
Elements are broadly classified into metals and non-metals based on their physical and chemical properties.
| Metals | Non-Metals |
|---|---|
| Good conductors of heat and electricity. | Poor conductors of heat and electricity. |
| Malleable and ductile. | Brittle in solid state. |
| Lustrous surface. | Usually dull. |
| Produce a ringing sound. | Do not produce a ringing sound. |
- Mercury is the only metal that is liquid at room temperature.
- Bromine is the only non-metal that is liquid at room temperature.
- Graphite is a non-metal but conducts electricity.
Quick Revision
- Liquid Metal → Mercury
- Liquid Non-metal → Bromine
- Graphite → Conducts Electricity
Acids, Bases and Salts
Acids, bases and salts are important classes of chemical substances. They differ in taste, chemical properties and their effect on indicators.
| Acids | Bases | Salts |
|---|---|---|
| Sour in taste. | Bitter in taste. | Formed by neutralization. |
| Turn blue litmus red. | Turn red litmus blue. | Generally neutral. |
| Release H⁺ ions. | Release OH⁻ ions. | Contain positive & negative ions. |
- Hydrochloric Acid (HCl)
- Sulphuric Acid (H₂SO₄)
- Nitric Acid (HNO₃)
- Sodium Hydroxide (NaOH)
- Calcium Hydroxide [Ca(OH)₂]
- Sodium Chloride (NaCl)
📘 Neutralization Reaction
Acid + Base → Salt + WaterQuick Revision
- Acid → Blue Litmus turns Red
- Base → Red Litmus turns Blue
- Salt → Neutralization Product
pH Scale
The pH scale measures the acidity or alkalinity of a solution. The scale ranges from 0 to 14.
| pH Value | Nature |
|---|---|
| Less than 7 | Acidic |
| 7 | Neutral |
| Greater than 7 | Basic (Alkaline) |
- Pure water has a pH of 7.
- Lemon juice is acidic.
- Soap solution is basic.
- The pH scale was introduced by S. P. L. Sørensen.
Quick Revision
- Acid → pH < 7
- Neutral → pH = 7
- Base → pH > 7
Important Chemical Compounds
| Compound | Chemical Formula | Common Use |
|---|---|---|
| Water | H₂O | Drinking, domestic use |
| Carbon Dioxide | CO₂ | Fire extinguishers, photosynthesis |
| Ammonia | NH₃ | Fertilizers |
| Methane | CH₄ | Fuel |
| Common Salt | NaCl | Food seasoning |
| Baking Soda | NaHCO₃ | Baking, antacids |
| Washing Soda | Na₂CO₃·10H₂O | Cleaning agent |
| Bleaching Powder | CaOCl₂ | Water purification |
| Plaster of Paris | CaSO₄·½H₂O | Medical casts, moulds |
| Gypsum | CaSO₄·2H₂O | Cement industry |
- Water → H₂O
- Carbon Dioxide → CO₂
- Ammonia → NH₃
- Methane → CH₄
- Common Salt → NaCl
- Baking Soda → NaHCO₃
- Bleaching Powder → CaOCl₂
- Plaster of Paris → CaSO₄·½H₂O
📘 Remember
POP → CaSO₄·½H₂OGypsum → CaSO₄·2H₂O
Baking Soda → NaHCO₃
Washing Soda → Na₂CO₃·10H₂O
Quick Revision
- Water → H₂O
- Common Salt → NaCl
- Ammonia → NH₃
- Methane → CH₄
- POP → CaSO₄·½H₂O
Chemical Reactions
A chemical reaction is a process in which one or more substances are converted into new substances with different chemical properties. During a chemical reaction, atoms are rearranged, but they are neither created nor destroyed.
- Types of Chemical Reactions
- Combination Reaction
- Decomposition Reaction
- Displacement Reaction
- Neutralization Reaction
| Reaction Type | Example |
|---|---|
| Combination | 2H₂ + O₂ → 2H₂O |
| Decomposition | CaCO₃ → CaO + CO₂ |
| Displacement | Zn + CuSO₄ → ZnSO₄ + Cu |
| Neutralization | HCl + NaOH → NaCl + H₂O |
- Chemical reactions involve the formation of new substances.
- Mass is conserved during a chemical reaction.
- Chemical equations should always be balanced.
Quick Revision
- New Substance → Chemical Reaction
- Mass Conserved → Yes
- Balanced Equation → Correct Equation
Oxidation and Reduction (Redox Reactions)
Oxidation and reduction are important chemical processes that usually occur together in a redox reaction.
| Process | Meaning |
|---|---|
| Oxidation | Addition of oxygen or removal of hydrogen. |
| Reduction | Removal of oxygen or addition of hydrogen. |
- Rusting of iron is an oxidation process.
- Extraction of metals from ores involves reduction.
📘 Remember
Oxidation → Oxygen AddedReduction → Oxygen Removed
Quick Revision
- Oxidation → Oxygen Gain
- Reduction → Oxygen Loss
Corrosion
Corrosion is the slow deterioration of metals due to chemical reactions with air, moisture or other environmental substances. The most common example is the rusting of iron.
| Metal | Corrosion Product |
|---|---|
| Iron | Rust |
| Silver | Black Silver Sulphide Layer |
| Copper | Green Copper Carbonate Layer |
- Painting
- Galvanization
- Electroplating
- Oiling and Greasing
Quick Revision
- Iron → Rust
- Silver → Black Coating
- Copper → Green Coating
Alloys
An alloy is a homogeneous mixture of two or more metals, or a metal with a non-metal, prepared to improve strength, hardness, corrosion resistance or other properties.
| Alloy | Composition |
|---|---|
| Brass | Copper + Zinc |
| Bronze | Copper + Tin |
| Steel | Iron + Carbon |
| Stainless Steel | Iron + Chromium + Nickel |
| Solder | Lead + Tin |
Quick Revision
- Brass → Copper + Zinc
- Bronze → Copper + Tin
- Steel → Iron + Carbon
Fuels
A fuel is a substance that produces heat energy when burned. Fuels are used in homes, industries, power plants and vehicles.
| Type | Examples |
|---|---|
| Solid Fuels | Wood, Coal |
| Liquid Fuels | Petrol, Diesel, Kerosene |
| Gaseous Fuels | LPG, CNG, Biogas |
- LPG mainly contains propane and butane.
- CNG is considered a cleaner fuel than petrol and diesel.
- Biogas is produced from the decomposition of organic waste.
Quick Revision
- LPG → Domestic Fuel
- CNG → Cleaner Fuel
- Biogas → Renewable Fuel
Everyday Chemistry
Chemistry plays an important role in our daily life. Many household products, medicines and food items are based on chemical principles.
| Substance | Main Use |
|---|---|
| Baking Soda | Baking, Antacid |
| Bleaching Powder | Disinfection & Water Purification |
| Plaster of Paris | Medical Casts & Decorative Items |
| Vinegar | Food Preservation |
| Soap | Cleaning Agent |
| Detergent | Washing Clothes |
- Milk of Magnesia is used as an antacid.
- Bleaching powder is used to disinfect drinking water.
- Vinegar contains acetic acid.
- Lemon contains citric acid.
- Tamarind contains tartaric acid.
📘 Remember
Vinegar → Acetic AcidLemon → Citric Acid
Curd → Lactic Acid
Tamarind → Tartaric Acid
Quick Revision
- Antacid → Milk of Magnesia
- Water Purification → Bleaching Powder
- Lemon → Citric Acid
- Curd → Lactic Acid
Important Scientists and Their Discoveries
Many Chemistry questions in SSC, Railway, Banking, Defence and Police examinations are based on famous scientists and their discoveries. Learning these discoveries helps in quick revision.
| Scientist | Contribution |
|---|---|
| John Dalton | Atomic Theory |
| Dmitri Mendeleev | Periodic Table |
| Henry Moseley | Modern Periodic Law |
| J. J. Thomson | Discovery of Electron |
| Ernest Rutherford | Discovery of Atomic Nucleus & Proton |
| James Chadwick | Discovery of Neutron |
| Niels Bohr | Bohr’s Atomic Model |
| Antoine Lavoisier | Law of Conservation of Mass |
| Amedeo Avogadro | Avogadro’s Law |
| Robert Boyle | Boyle’s Law |
- Antoine Lavoisier is known as the Father of Modern Chemistry.
- Dmitri Mendeleev is known as the Father of the Periodic Table.
- Henry Moseley arranged elements according to atomic number.
Important Chemical Symbols
| Element | Symbol |
|---|---|
| Hydrogen | H |
| Oxygen | O |
| Nitrogen | N |
| Carbon | C |
| Sodium | Na |
| Potassium | K |
| Calcium | Ca |
| Iron | Fe |
| Copper | Cu |
| Silver | Ag |
| Gold | Au |
| Mercury | Hg |
| Lead | Pb |
| Tin | Sn |
| Zinc | Zn |
Quick Revision
- Sodium → Na
- Potassium → K
- Iron → Fe
- Copper → Cu
- Silver → Ag
- Gold → Au
- Mercury → Hg
Most Important Chemical Formulae
Hydrogen → H₂
Oxygen → O₂
Nitrogen → N₂
Carbon Dioxide → CO₂
Carbon Monoxide → CO
Ammonia → NH₃
Methane → CH₄
Hydrochloric Acid → HCl
Sulphuric Acid → H₂SO₄
Nitric Acid → HNO₃
Sodium Hydroxide → NaOH
Calcium Carbonate → CaCO₃
Common Salt → NaCl
Baking Soda → NaHCO₃
Washing Soda → Na₂CO₃·10H₂O
Bleaching Powder → CaOCl₂
Plaster of Paris → CaSO₄·½H₂O
📌 One-Minute Revision
- ✔ Matter has mass and occupies space.
- ✔ Solids have a fixed shape and fixed volume.
- ✔ Atoms are the smallest units of elements.
- ✔ Atomic Number = Number of Protons.
- ✔ Groups = 18 | Periods = 7.
- ✔ Mercury is the only liquid metal at room temperature.
- ✔ Bromine is the only liquid non-metal at room temperature.
- ✔ Graphite conducts electricity.
- ✔ Acid turns blue litmus red.
- ✔ Base turns red litmus blue.
- ✔ pH of pure water = 7.
- ✔ Water = H₂O.
- ✔ Common Salt = NaCl.
- ✔ Baking Soda = NaHCO₃.
- ✔ Plaster of Paris = CaSO₄·½H₂O.
- ✔ Rusting is an oxidation process.
- ✔ Brass = Copper + Zinc.
- ✔ Bronze = Copper + Tin.
- ✔ LPG mainly contains propane and butane.
- ✔ Father of Modern Chemistry = Antoine Lavoisier.
Most Frequently Asked Chemistry Facts
Conclusion
Chemistry is one of the highest-scoring sections of General Science in SSC, Railway, Banking, Defence, Police and State Government examinations. A clear understanding of matter, atomic structure, the periodic table, acids, bases, salts, chemical reactions and important compounds helps candidates answer objective questions with confidence.
Regular revision of chemical symbols, formulas, scientists, important compounds and everyday chemistry can significantly improve your performance in competitive exams. After completing these notes, practice topic-wise MCQs to strengthen your concepts and improve speed.
These Chemistry Notes are designed to provide simple, exam-oriented study material for beginners as well as competitive exam aspirants. Bookmark this page for quick revision and continue practicing regularly to achieve better results.