Topic overview

Start with the big picture

An atom contains a nucleus of protons and neutrons, surrounded by electrons in orbitals. The proton count defines the element, while differences in neutron count create isotopes that can support radiolabeling and tracing. Electron configurations and valence electrons help explain bonding and reactivity. The topic then develops orbital shapes, hybridization, molecular geometry, and sigma and pi bonds. It compares ionic, covalent, and coordinate bonding, and examines how electronegativity, bond order, formal charge, resonance, and inductive or mesomeric effects influence molecular structure and electron distribution. Intermolecular forces, hydrogen bonding, acidity and basicity, and bond energies extend these principles to chemical behavior. The lesson also connects atomic and bonding concepts to pharmaceutical relevance.