Chemistry Basics – Quick & Easy Study Notes
(For Puducherry PSC – General Awareness & Current Affairs)
Goal: Know the very building blocks of chemistry so you can answer simple questions on the exam.
Tip: Think of chemistry as the “recipe book” of everything around us.
1. What is Chemistry?
- Chemistry = science that studies what things are made of and how they change.
- Everyday example: Baking a cake – you mix flour, sugar, eggs, and heat it. Chemistry tells us why the cake rises and turns golden.
2. Atoms & Elements
| Term | Simple Idea | Everyday Analogy |
|---|---|---|
| Atom | Smallest unit of a substance that keeps its identity. | A Lego block – the smallest piece that still looks like a block. |
| Element | A pure substance made of only one kind of atom. | A single color of paint – all paint of that color is the same element. |
- Example: Hydrogen atom = one proton + one electron.
- Every element has a symbol (e.g., H for Hydrogen, O for Oxygen).
3. The Periodic Table – “Alphabet of Elements”
- Rows = Periods (1–7).
- Columns = Groups (1–18).
- The table is arranged by increasing atomic number (protons in the nucleus).
Why it matters:
- Elements in the same group share similar “behaviours” (like how all oranges are sweet).
- Helps predict properties of unknown elements.
4. Molecules & Compounds
- Molecule = two or more atoms bound together.
- Compound = a molecule with atoms of two or more different elements.
| Example | How it forms | Everyday Analogy |
|---|---|---|
| Water (H₂O) | Two H + one O | Two cups of milk + one cup of juice = smoothie. |
| Salt (NaCl) | Sodium + Chlorine | Two different stickers glued together. |
5. Chemical Reactions – “Ingredient Swap”
- Reactants → process → Products.
- Think of it as a recipe: when you stir sugar into tea, the sugar dissolves – a change happens.
Key idea:
- The total number of atoms on each side stays the same (law of conservation of mass).
6. States of Matter – “Modes of Living”
| State | How atoms behave | Everyday Example |
|---|---|---|
| Solid | Packed tightly, small movement | Ice cube |
| Liquid | Close but can flow | Water |
| Gas | Far apart, moves freely | Steam |
- Temperature and pressure decide the state.
7. Acids & Bases – “Taste Test”
| Term | Simple Description | Everyday Example |
|---|---|---|
| Acid | Tastes sour; reacts with metals. | Lemon juice |
| Base | Tastes bitter; feels slippery. | Soap |
- pH scale (0–14) tells how acidic or basic something is.
- pH < 7 → Acidic
- pH = 7 → Neutral (pure water)
- pH > 7 → Basic
8. Quick Review – “Flashcards”
| Question | Answer |
|---|---|
| What is an atom? | Smallest unit of a substance. |
| Give an example of a compound. | Water (H₂O). |
| What does the periodic table show? | All known elements arranged by atomic number. |
| Which state is ice? | Solid. |
| What is pH 3? | Acidic. |
| What stays the same in a chemical reaction? | Number of atoms. |
9. Tiny Practical Example
Problem: You have 2 g of sodium (Na) and 1 g of chlorine gas (Cl₂).
- Step 1: Find how many moles each has.
- Na: 2 g ÷ 23 g/mol ≈ 0.087 mol
- Cl₂: 1 g ÷ 71 g/mol ≈ 0.014 mol
- Step 2: Reaction: 2 Na + Cl₂ → 2 NaCl
- Step 3: Limiting reactant? Cl₂ is less (0.014 mol) → it limits the reaction.
- Result: 0.014 mol Cl₂ can make 0.014 mol NaCl.
- Mass of NaCl produced: 0.014 mol × 58.5 g/mol ≈ 0.82 g.
Takeaway: Simple arithmetic + the balanced equation gives the answer.
10. Why This Helps for the PSC
- Many general‑awareness questions ask: “What is a chemical compound?”
- Current affairs: recall recent chemical advances (e.g., new battery chemistries, green chemistry).
- Having a clear mental picture of atoms, molecules, and reactions lets you answer confidently.
Quick Mnemonic
Atoms Establish Molecules, Chemical Reactions Shake Phases, Acids & Bases PeaL.
(A‑E‑M‑C‑R‑S‑P‑A‑B‑P)
“Atoms, Elements, Molecules, Chemistry, Reactions, States, Acids, Bases, P‑hew!”
Use it to remember the order of key concepts.
Final Thought:
Think of chemistry as the language that lets us describe how everything in the world comes together, behaves, and transforms. Master the basics, and the rest will follow!