⚗️ CHEMISTRY – SUMMARY NOTES
🧠 1. What Is Chemistry?
Chemistry is the branch of science that studies the composition, structure, properties, and changes of matter.
Word origin: Khemeia (Greek) – the art of transmutation of matter.
🧬 2. Branches of Chemistry
| Branch | Focus Area |
|---|---|
| Physical Chemistry | Laws, theories, energy, and matter behavior |
| Inorganic Chemistry | Study of elements and inorganic compounds |
| Organic Chemistry | Study of carbon and its compounds |
| Analytical Chemistry | Analysis of substances |
| Biochemistry | Chemistry of living organisms |
| Industrial Chemistry | Chemical processes in industries |
🌡️ 3. Matter and Its States
Matter: Anything that has mass and occupies space.
Three main states:
- Solid – definite shape & volume
- Liquid – definite volume, no fixed shape
- Gas – no fixed shape or volume
Other states: Plasma, Bose–Einstein Condensate.
Physical vs. Chemical Change:
| Physical Change | Chemical Change |
|---|---|
| No new substance | New substance formed |
| Reversible | Irreversible |
| e.g., melting ice | burning paper |
⚖️ 4. Laws of Chemical Combination
| Law | Statement | Scientist |
|---|---|---|
| Law of Conservation of Mass | Mass is neither created nor destroyed | Lavoisier |
| Law of Constant Proportion | Elements combine in fixed ratios by mass | Proust |
| Law of Multiple Proportion | Same elements form different compounds in small ratios | Dalton |
| Law of Reciprocal Proportion | Elements combine in simple ratios | Richter |
| Gay-Lussac’s Law | Gaseous volumes combine in simple ratios | Gay-Lussac |
⚛️ 5. Atomic Structure
- Atom: Smallest particle of an element that retains its properties.
- Subatomic Particles:
| Particle | Symbol | Charge | Mass (approx.) |
|---|---|---|---|
| Proton | p⁺ | +1 | 1 amu |
| Neutron | n⁰ | 0 | 1 amu |
| Electron | e⁻ | –1 | 1/1836 amu |
Atomic Number (Z): Number of protons
Mass Number (A): Protons + Neutrons
Isotopes: Same element, different neutrons (e.g., H₁, H₂, H₃)
Isobars: Different elements, same mass number
🌠 6. Atomic Models
| Model | Scientist | Description |
|---|---|---|
| Dalton’s Model | John Dalton | Atom is indivisible |
| Thomson’s Model | J.J. Thomson | Plum pudding model (electrons in a sphere of + charge) |
| Rutherford’s Model | Ernest Rutherford | Nucleus at center; electrons revolve |
| Bohr’s Model | Niels Bohr | Electrons in fixed energy levels |
| Quantum Model | Schrödinger, Heisenberg | Probability-based electron cloud |
Bohr’s energy formula:En=−13.6Z2n2 eVEn=−13.6n2Z2 eV
🧩 7. Atomic Number, Valency & Chemical Formula
Valency: Combining capacity of an atom.
Ions:
- Cation (+): loses electron (e.g., Na⁺)
- Anion (–): gains electron (e.g., Cl⁻)
Formula formation rule:
Criss-cross charges → e.g., Na++Cl−→NaClNa++Cl−→NaCl
🧪 8. Mole Concept
1 mole = 6.022×10236.022×1023 particles (Avogadro’s number)
Formulas:No. of moles=Given massMolar massNo. of moles=Molar massGiven massMass=Moles×Molar massMass=Moles×Molar massNo. of particles=Moles×6.022×1023No. of particles=Moles×6.022×1023
🌬️ 9. Structure of Matter (Molecules & Compounds)
| Term | Meaning | Example |
|---|---|---|
| Element | Pure substance of one type of atom | O₂, N₂ |
| Compound | 2+ elements chemically combined | H₂O, CO₂ |
| Mixture | 2+ substances physically mixed | Air, salt water |
🔥 10. Chemical Reactions
Chemical Equation:Reactants→ProductsReactants→Products
Types:
- Combination: A + B → AB
- Decomposition: AB → A + B
- Single Displacement: A + BC → AC + B
- Double Displacement: AB + CD → AD + CB
- Combustion: Hydrocarbon + O₂ → CO₂ + H₂O
- Redox: Oxidation (loss of e⁻) & Reduction (gain of e⁻)
Balancing Rule: Equal number of each atom on both sides.
⚡ 11. Acids, Bases, and Salts
| Property | Acids | Bases |
|---|---|---|
| Taste | Sour | Bitter |
| pH | < 7 | > 7 |
| Litmus | Blue → Red | Red → Blue |
| Ion produced | H⁺ | OH⁻ |
pH Scale: 0–14
7 = Neutral (e.g., water)
<7 = Acidic; >7 = Basic
Salt formation:
Acid + Base → Salt + Water
Examples:
- HCl + NaOH → NaCl + H₂O
- H₂SO₄ + KOH → K₂SO₄ + H₂O
🌍 12. The Periodic Table
Modern Periodic Law:
Properties of elements are a periodic function of their atomic numbers. — Mendeleev & Moseley
Groups: Vertical columns (1–18)
Periods: Horizontal rows (1–7)
Types of Elements:
- Metals – good conductors (Na, Fe)
- Non-metals – poor conductors (O, S)
- Metalloids – intermediate (Si, Ge)
Trends:
| Property | Across a Period | Down a Group |
|---|---|---|
| Atomic size | ↓ | ↑ |
| Ionization energy | ↑ | ↓ |
| Metallic character | ↓ | ↑ |
🔗 13. Chemical Bonding
Types:
- Ionic bond – electron transfer (NaCl)
- Covalent bond – electron sharing (H₂, O₂, CH₄)
- Metallic bond – free electrons among metal ions
Octet Rule: Atoms combine to have 8 electrons in outer shell.
🌡️ 14. States of Matter & Gas Laws
Boyle’s Law:
P∝1/VP∝1/V (at constant T)
Charles’s Law:
V∝TV∝T (at constant P)
Avogadro’s Law:
Equal volumes of gases contain equal number of molecules (at same T & P)
Ideal Gas Law:PV=nRTPV=nRT
🔥 15. Heat & Thermodynamics in Chemistry
| Concept | Formula | Unit |
|---|---|---|
| Heat change (Q) | Q=mcΔTQ=mcΔT | Joule |
| Enthalpy (ΔH) | Heat change at constant pressure | kJ/mol |
Exothermic: Heat released (–ΔH)
Endothermic: Heat absorbed (+ΔH)
🌿 16. Organic Chemistry Basics
Organic Compounds: Contain carbon & hydrogen.
| Type | General Formula | Example |
|---|---|---|
| Alkanes | CₙH₂ₙ₊₂ | CH₄ (Methane) |
| Alkenes | CₙH₂ₙ | C₂H₄ (Ethene) |
| Alkynes | CₙH₂ₙ₋₂ | C₂H₂ (Ethyne) |
| Alcohols | R–OH | C₂H₅OH |
| Acids | R–COOH | CH₃COOH |
Functional groups: –OH, –COOH, –CHO, –CO–, –NH₂, etc.
🧴 17. Solutions and Concentration
| Term | Definition |
|---|---|
| Solution | Homogeneous mixture |
| Solute | Substance dissolved |
| Solvent | Medium of dissolution |
| Concentration | Amount of solute in given solution |
Concentration formulas:Molarity (M)=moles of solutelitres of solutionMolarity (M)=litres of solutionmoles of soluteMass %=mass of solutemass of solution×100Mass %=mass of solutionmass of solute×100
🧲 18. Electrochemistry (Basics)
- Electrolysis: Decomposition using electric current
- Anode: Positive electrode
- Cathode: Negative electrode
- Electroplating: Coating metal using electricity
Example:
Electrolysis of water → 2H2O→2H2+O22H2O→2H2+O2
🧬 19. Environmental Chemistry
| Concept | Example |
|---|---|
| Air pollution | CO₂, NOₓ, SO₂ |
| Water pollution | Industrial waste, fertilizers |
| Green chemistry | Eco-friendly synthesis |
| Ozone layer depletion | CFCs (chlorofluorocarbons) |
🔢 20. Important Constants
| Constant | Symbol | Value |
|---|---|---|
| Avogadro’s number | Nₐ | 6.022×10236.022×1023 |
| Gas constant | R | 8.314 J/mol·K |
| 1 atm pressure | – | 101.325 kPa |
| 1 mole gas volume (STP) | – | 22.4 L |
🧭 21. Chemistry in Daily Life
- Soap & Detergents: Surfactants remove dirt
- Medicine: Drugs like aspirin, paracetamol
- Fertilizers: Urea, NPK
- Polymers: Plastic, nylon, rubber
- Food Chemistry: Preservatives, additives
✅ 22. Summary Table
| Topic | Key Formula / Concept |
|---|---|
| Mole Concept | n=mMn=Mm |
| Gas Law | PV=nRTPV=nRT |
| pH | −log[H+]−log[H+] |
| Molarity | M=nVM=Vn |
| Enthalpy | ΔH=H2−H1ΔH=H2−H1 |
| Ideal Gas | 1 mole gas = 22.4 L (STP) |
| Energy Levels | En=−13.6Z2n2En=−13.6n2Z2 |
🔬 23. Key Scientists
| Scientist | Contribution |
|---|---|
| Dalton | Atomic theory |
| Thomson | Discovery of electron |
| Rutherford | Nuclear model |
| Bohr | Energy levels |
| Mendeleev | Periodic table |
| Avogadro | Mole concept |
| Lavoisier | Law of mass conservation |
🌟 24. Recap
| Area | Core Idea |
|---|---|
| Matter | Everything around us |
| Atoms | Building blocks |
| Reactions | Transformation of matter |
| Periodic Law | Organized element properties |
| Bonding | Atoms form molecules |
| Energy | Heat, work, and reactions |
| Organic Chemistry | Carbon compounds |
| Daily Life Use | Medicines, fuel, food |