Principles of Chemistry
Atoms, formulae, and equations
Every atom has a nucleus with protons (positive) and neutrons (no charge). Electrons (negative) orbit in shells. Atomic number = protons. Mass number = protons + neutrons. Isotopes = same element, different neutrons.
The Periodic Table arranges elements by atomic number. Same group = same outer electrons, similar properties. Same period = same number of shells.
Ionic bonding: metals transfer electrons to non-metals, forming ions. NaCl: Na⁺Cl⁻. **Covalent bonding:** non-metals share electron pairs. H₂O, O₂.
Mole calculations: **Moles = mass ÷ molar mass**. Molar mass = relative formula mass in grams. Example: 44g of CO₂ (Mr = 44) = 1 mol. **Percentage composition** = mass of element ÷ total Mr × 100.
Key Points to Remember
- 1Atomic structure
- 2The Periodic Table
- 3Ionic and covalent bonding
- 4Calculations and moles
Pakistan Example
Salt from Khewra Salt Mine — Ionic Bonding in Action
Khewra Salt Mine in Punjab produces millions of tonnes of NaCl yearly. Sodium donates an electron to chlorine — ionic bonding. Every time a Pakistani family adds salt to biryani, they're using ionic chemistry formed hundreds of millions of years ago.
Quick Revision Infographic
Chemistry — Quick Revision
Principles of Chemistry
Key Concepts
Salt from Khewra Salt Mine — Ionic Bonding in Action
Khewra Salt Mine in Punjab produces millions of tonnes of NaCl yearly. Sodium donates an electron to chlorine — ionic bonding. Every time a Pakistani family adds salt to biryani, they're using ionic chemistry formed hundreds of millions of years ago.