CHEMISTRY – SHORT NOTES

1. Atomic Structure

• Atom = Proton (+), Neutron (0), Electron (–)

• Atomic number (Z) = No. of protons

• Mass number (A) = Protons + Neutrons

• Isotopes → Same Z, different A

• Orbitals → s (2e⁻), p (6e⁻), d (10e⁻), f (14e⁻)

2. Periodic Table

• Period → Horizontal rows

• Group → Vertical columns

• Atomic size ↓ down group, ↑ number of shells

• Ionization energy ↑ across period (left → right)

• Electronegativity highest → Fluorine (F)

3. Chemical Bonding

• Ionic bond: Electron transfer (NaCl)

• Covalent bond: Electron sharing (H₂, O₂)

• Metallic bond: Free electrons (metals)

• VSEPR theory → predicts shape

  • Linear → 180°

  • Trigonal planar → 120°

  • Tetrahedral → 109.5°

4. States of Matter

• Solid → Fixed shape, strong force

• Liquid → No fixed shape

• Gas → High compressibility

• Gas laws:

  • Boyle’s: P ∝ 1/V

  • Charles’: V ∝ T

  • Avogadro: V ∝ n

5. Chemical Reactions

• Combination → A + B → AB

• Decomposition → AB → A + B

• Displacement → A + BC → AC + B

• Redox → Oxidation + Reduction

Balancing Tip:

Same atoms on both sides → adjust coefficients.

6. Acids, Bases & Salts

• pH < 7 → Acid

• pH > 7 → Base

• pH = 7 → Neutral

• Strong acid → HCl, H₂SO₄

• Strong base → NaOH, KOH

7. Stoichiometry (Mole Concept)

• 1 mole = 6.022 × 10²³ particles

• Moles = Mass / Molar mass

• Volume at STP → 22.4 L per mole of gas

8. Organic Chemistry Basics

• Hydrocarbons → Compounds of C & H

• Alkane: CnH₂n+₂

• Alkene: CnH₂n

• Alkyne: CnH₂n−₂

• Functional groups:

  • Alcohol → –OH

  • Aldehyde → –CHO

  • Ketone → –CO–

  • Carboxylic acid → –COOH

9. Solutions

• Solute + Solvent → Solution

• Concentration → moles/liter (Molarity)

• Saturated solution → Max solute dissolved

10. Thermodynamics

• ΔH → Heat change

• Exothermic → Heat released (ΔH –ve)

• Endothermic → Heat absorbed (ΔH +ve)

• 1st Law → Energy cannot be created/destroyed