Chemistry is the branch of science that studies the composition, structure, properties, and transformations of matter. Chemistry focuses on basic concepts, real-life applications, and awareness of environmental and scientific developments.
Chemistry connects deeply to everyday life—whether through the food we eat, the air we breathe, the cleaning agents we use, or the medicines we take.
🔹 1. Matter and Its States
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Definition: Matter is anything that has mass and occupies space.
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States:
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Solid – Fixed shape and volume (e.g., Ice)
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Liquid – Fixed volume, no fixed shape (e.g., Water)
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Gas – No fixed shape or volume (e.g., Oxygen)
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Plasma – Found in lightning, stars
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Bose-Einstein Condensate – Supercooled matter at near absolute zero
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📌 Example: Water can exist as ice (solid), liquid water, and steam (gas).
🔹 2. Atoms and Molecules
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Atom: The smallest unit of an element.
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Molecule: A combination of two or more atoms chemically bonded.
📌 Examples:
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H₂O: Water molecule (2 hydrogen + 1 oxygen)
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O₂: Oxygen molecule
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CO₂: Carbon dioxide
🔹 3. Elements, Compounds, and Mixtures
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Element: Pure substance with one type of atom (e.g., Gold, Oxygen).
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Compound: Two or more elements chemically combined (e.g., NaCl – Salt).
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Mixture: Physical blend of substances (e.g., Air, Saltwater).
🔹 4. Acids, Bases, and Salts
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Acids: Sour taste, turn blue litmus red (e.g., HCl, citric acid in lemon).
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Bases: Bitter, slippery, turn red litmus blue (e.g., NaOH, baking soda).
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Salts: Formed from acid-base neutralization (e.g., NaCl).
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pH Scale: Ranges from 0 (acidic) to 14 (basic); 7 is neutral.
📌 Example: Vinegar contains acetic acid; soap is basic in nature.
🔹 5. Periodic Table
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Organized by atomic number.
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Groups elements into metals, non-metals, and noble gases.
📌 Examples:
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Metals: Iron (Fe), Copper (Cu)
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Non-metals: Oxygen (O), Sulfur (S)
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Noble Gases: Helium (He), Neon (Ne)
🧑🔬 Scientist: Dmitri Mendeleev developed the Periodic Table.
🔹 6. Chemical Reactions
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Types:
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Combination
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Decomposition
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Displacement
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Neutralization
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Combustion
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📌 Example:
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Rusting: Iron + Water + Oxygen → Iron oxide (Fe₂O₃)
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Neutralization: HCl + NaOH → NaCl + H₂O
🔹 7. Water and Air Chemistry
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Water: Universal solvent; purification methods include boiling, filtration, and chlorination.
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Air Composition:
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Nitrogen (78%)
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Oxygen (21%)
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Other gases (1%)
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📌 Example: Chlorine is added to drinking water to kill germs.
🔹 8. Environmental Chemistry
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Greenhouse Gases: CO₂, CH₄, N₂O cause global warming.
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Acid Rain: Caused by SO₂ and NO₂ reacting with rainwater.
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Ozone Layer: Protects against UV rays; damaged by CFCs.
📌 Example: CFCs from old refrigerators deplete the ozone layer.
🔹 9. Everyday Chemistry
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Toothpaste: Contains fluoride to prevent cavities.
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Soap and Detergents: Remove grease using surfactants.
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Fertilizers: Provide nitrogen (urea), phosphorus, and potassium.
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Medicines: Include antibiotics (e.g., penicillin), antiseptics (e.g., iodine).
📌 Example: Paracetamol is used as a fever reducer and pain reliever.
🔹 10. Famous Scientists in Chemistry
| Scientist | Contribution |
|---|---|
| Antoine Lavoisier | Law of Conservation of Mass |
| Dmitri Mendeleev | Periodic Table |
| Marie Curie | Discovery of radioactivity |
| Linus Pauling | Study of chemical bonds |
🧪 Important Elements of the Periodic Table
| Element Name | Symbol | Atomic Number | Common Use / Fact |
|---|---|---|---|
| Hydrogen | H | 1 | Lightest element; used in fuel cells and rocket fuel |
| Helium | He | 2 | Inert gas used in balloons and cryogenics |
| Lithium | Li | 3 | Used in batteries (Li-ion), mood stabilizers |
| Carbon | C | 6 | Found in all living organisms; used in fuels |
| Nitrogen | N | 7 | 78% of Earth's atmosphere; used in fertilizers |
| Oxygen | O | 8 | Essential for respiration; used in medical oxygen |
| Fluorine | F | 9 | Used in toothpaste (fluoride) and Teflon coatings |
| Neon | Ne | 10 | Used in neon lights and advertising signs |
| Sodium | Na | 11 | Found in table salt (NaCl); reactive metal |
| Magnesium | Mg | 12 | Used in fireworks and medicines (e.g., antacids) |
| Aluminum | Al | 13 | Lightweight metal used in cans, aircraft |
| Silicon | Si | 14 | Used in electronics and semiconductors |
| Phosphorus | P | 15 | Used in fertilizers, detergents, and matches |
| Sulfur | S | 16 | Used in making sulfuric acid; matches, fungicides |
| Chlorine | Cl | 17 | Disinfectant in water; used in PVC plastic |
| Argon | Ar | 18 | Inert gas used in welding and bulbs |
| Potassium | K | 19 | Essential nutrient; used in fertilizers |
| Calcium | Ca | 20 | Found in bones, teeth; used in cement |
| Iron | Fe | 26 | Core component of steel; essential mineral |
| Copper | Cu | 29 | Excellent conductor; used in electrical wiring |
| Zinc | Zn | 30 | Used in galvanization; immune support |
| Silver | Ag | 47 | Used in jewelry, coins, photography |
| Tin | Sn | 50 | Used in cans, alloys, soldering |
| Iodine | I | 53 | Antiseptic; essential for thyroid health |
| Gold | Au | 79 | Precious metal for jewelry, electronics |
| Mercury | Hg | 80 | Only metal that is liquid at room temperature; toxic |
| Lead | Pb | 82 | Heavy metal; used in batteries, but toxic |
| Uranium | U | 92 | Used as nuclear fuel |
📌 Tips to Remember Important Elements
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Group 1 (Alkali Metals): H, Li, Na, K – very reactive, found in salts and batteries
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Group 17 (Halogens): F, Cl, I – form salts, used in disinfectants
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Group 18 (Noble Gases): He, Ne, Ar – inert, used in lighting and electronics
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Transition Metals: Fe, Cu, Zn, Ag, Au – conduct electricity, used in tools and jewelry
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Non-Metals: H, C, N, O, P, S – essential for life and agriculture
📝 Practice MCQs (With Answers and Explanations)
1. Which of the following is a noble gas?
A) Oxygen
B) Nitrogen
C) Helium
D) Hydrogen
✅ Answer: C) Helium
📌 Explanation: Noble gases are inert and found in Group 18 of the periodic table.
2. Which acid is present in lemon juice?
A) Hydrochloric acid
B) Citric acid
C) Sulfuric acid
D) Acetic acid
✅ Answer: B) Citric acid
📌 Explanation: Citric acid occurs naturally in citrus fruits.
3. Rusting of iron is a type of:
A) Combination reaction
B) Decomposition reaction
C) Redox reaction
D) Displacement reaction
✅ Answer: C) Redox reaction
📌 Explanation: Rusting involves oxidation of iron in the presence of water and oxygen.
4. What is the pH value of pure water?
A) 1
B) 7
C) 10
D) 14
✅ Answer: B) 7
📌 Explanation: A pH of 7 indicates neutrality—pure water is neither acidic nor basic.
5. Who is known as the 'Father of the Periodic Table'?
A) John Dalton
B) Dmitri Mendeleev
C) Marie Curie
D) Lavoisier
✅ Answer: B) Dmitri Mendeleev
📌 Explanation: Mendeleev organized elements by atomic mass in the first periodic table.
6. Which gas is responsible for causing acid rain?
A) Oxygen
B) Carbon monoxide
C) Sulfur dioxide
D) Nitrogen gas
✅ Answer: C) Sulfur dioxide
📌 Explanation: SO₂ reacts with water vapor to form sulfuric acid in rain.
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