---
tags:
  - science/chemistry
  - atoms
  - bonds
created: 2026-05-16
breadcrumb: "Chemistry > Atoms & bonding > Atoms & chemical bonds"
---

# Atoms & chemical bonds

> **Mechanism:** Electron sharing & transfer between nuclei

## Items

- **Atom** — Nucleus (protons + neutrons) surrounded by electrons. Atomic number = proton count.
- **Isotope** — Same Z, different N. Same chemistry, different mass.
- **Electron shell** — Energy levels around the nucleus. Outer shell electrons drive chemistry.
- **Ionic bond** — Full transfer of electrons; opposite ions attract (NaCl).
- **Covalent bond** — Shared electron pair between atoms (H₂O, CO₂).
- **Metallic bond** — Delocalised "sea" of electrons; explains conductivity and ductility.
- **Hydrogen bond** — Weak electrostatic attraction; gives water its high boiling point.

## Related

- [[reactions]]
- [[periodic-table]]