Atomic Structure & Bonding
Electron configurations, ionic/covalent/metallic bonding
Every atom has a nucleus containing protons and neutrons, surrounded by electrons in energy levels. At A Level, we describe positions using subshells — s, p, and d.
Electron Configuration: Fill subshells in order: **1s → 2s → 2p → 3s → 3p → 4s → 3d**. Each s holds 2, p holds 6, d holds 10. Sodium (Na, 11): **1s² 2s² 2p⁶ 3s¹**.
Ionic Bonding: Metals *transfer* electrons to non-metals. Opposite charges attract. NaCl: Na⁺Cl⁻. High melting points, conduct when dissolved.
Covalent Bonding: Non-metals *share* electron pairs. Water (H₂O) has two single bonds. Generally poor conductors, lower melting points.
Metallic Bonding: Outer electrons form a **sea of delocalised electrons** around positive ions. Explains conductivity, malleability, high melting points.
Key Points to Remember
- 1Electron configuration using s, p, d notation
- 2Ionic bonding: transfer of electrons
- 3Covalent bonding: sharing of electrons
- 4Metallic bonding: sea of delocalised electrons
Pakistan Example
Salt in Lahore's Food Street — Ionic Bonding at Work
The salt on Lahore's chaat is NaCl — ionic bonding. Sodium transfers one electron to chlorine, creating ions that attract strongly. Meanwhile, copper wires in every Karachi kitchen demonstrate metallic bonding with free electrons flowing like traffic on the M2.