Atomic Structure
Year 8 ⚛️ Particles & Structure State the charges and masses of protons, neutrons and electrons; use atomic number and mass number.
⚛️ Protons, Neutrons & Electrons
Every atom has a nucleus containing protons and neutrons, with electrons in shells around it.
Key Definitions
$$\text{Atomic number } Z = \text{number of protons}$$
$$\text{Mass number } A = \text{protons} + \text{neutrons}$$
$$\text{Neutrons} = A - Z$$Sodium (Na): Z = 11, A = 23 → 11 protons, 12 neutrons, 11 electrons.
🔄 Electron Shells & Configurations
Electrons fill shells in order starting from the innermost.
| Shell | Max electrons | Elements filling this shell |
|---|---|---|
| 1st (innermost) | 2 | H (1), He (2) |
| 2nd | 8 | Li (2,1) to Ne (2,8) |
| 3rd | 8 (for Z ≤ 20) | Na (2,8,1) to Ar (2,8,8) |
Common configurations: C: 2,4 | O: 2,6 | Na: 2,8,1 | Cl: 2,8,7 | Ca: 2,8,8,2
🔬 Isotopes
Isotopes are atoms of the same element with the same atomic number but different mass numbers (different neutron count). They have identical chemical properties.
Carbon isotopes: ¹²C (6p, 6n), ¹³C (6p, 7n), ¹⁴C (6p, 8n, radioactive).
Chlorine: ³⁵Cl (75%) + ³⁷Cl (25%) → Ar = (35×75 + 37×25)/100 = 35.5
Chlorine: ³⁵Cl (75%) + ³⁷Cl (25%) → Ar = (35×75 + 37×25)/100 = 35.5
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Interactive Demonstration — Atomic Structure
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