Atoms and the Periodic Table

Everything in the universe — your shoes, the stars, the air — is made of ATOMS. Atoms are mind-blowingly tiny (millions fit on the head of a pin). Scientists have spent 200 years discovering their structure. This is the foundation of ALL chemistry.

Every atom has three parts:\n\n**1. PROTONS** — positive charge (+). In the nucleus.\n**2. NEUTRONS** — no charge (0). Also in the nucleus.\n**3. ELECTRONS** — negative charge (-). Orbit the nucleus.\n\nThe number of PROTONS tells you which ELEMENT the atom is:\n\n- 1 proton = Hydrogen\n- 6 protons = Carbon (you!)\n- 8 protons = Oxygen (the air!)\n- 26 protons = Iron\n- 79 protons = Gold

The PERIODIC TABLE organizes all the known elements by their number of protons.\n\n- Each square = one element\n- Number at top = atomic number (# of protons)\n- Letter = element symbol (H = Hydrogen, O = Oxygen, Au = Gold)\n- Number at bottom = atomic mass\n\nIt is NOT a random list — elements with similar properties are in the same COLUMN (group).

**PERIODS** (rows) — each row represents energy levels of electrons.\n\n**GROUPS** (columns) — elements in the same column behave ALIKE chemically.\n\nFamous groups:\n- **Alkali Metals** (Group 1) — react violently with water (Sodium, Potassium)\n- **Halogens** (Group 17) — reactive, like Chlorine\n- **Noble Gases** (Group 18) — DO NOT react (Helium, Neon, Argon)\n\nKnowing the group = knowing how the element behaves.

Atoms combine to form MOLECULES:\n\n- H₂O = water (2 hydrogens + 1 oxygen)\n- CO₂ = carbon dioxide\n- O₂ = oxygen gas\n- NaCl = salt (sodium + chlorine)\n- C₆H₁₂O₆ = glucose (sugar)\n\nAtoms form molecules by sharing or giving up ELECTRONS. This is called CHEMICAL BONDING.

Atoms of the same element CAN have different numbers of NEUTRONS. These are called ISOTOPES.\n\nExample: Carbon-12 (6 neutrons) is normal carbon. Carbon-14 (8 neutrons) is a rare isotope used to DATE ancient artifacts (carbon dating).\n\nSome isotopes are STABLE; others are radioactive.