Size & Mass of Atoms (OCR GCSE Chemistry A, Combined (Gateway Science Suite)): Revision Notes
📚 Revision Notes
1.1.8 Size & Mass of Atoms
The Size of the Nucleus Compared to the Atom
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The nucleus of an atom is extremely small in comparison to the atom as a whole.
- Size Comparisons:
- The radius of an atom is approximately 0.1 nanometers (nm) or 1 × 10⁻¹⁰ metres (m).
- The radius of the nucleus is even smaller, about 1 × 10⁻¹⁴ metres (m), which is less than 1/10,000 of the atom's radius.
- Contextual Comparisons:
- For perspective, the radius of a typical bacterium is about 1 × 10⁻⁶ metres (m), which is much larger than the size of an atom.
- The radius of a human hair is approximately 1 × 10⁻⁴ metres (m), which is significantly larger than even a bacterium.
Masses of Subatomic Particles
- The masses of subatomic particles are extremely small. Instead of expressing their actual masses in kilogrammes, we use their relative masses for simplicity.
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The relative mass of a proton is set to 1. Any particle with a relative mass smaller than 1 is less massive.
Relative Mass and Charge of Subatomic Particles:
| Subatomic Particle | Relative Mass | Relative Charge |
|---|---|---|
| Proton | 1 | +1 |
| Neutron | 1 | 0 |
| Electron | Very small | -1 |
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Key Points:
- The mass of an electron is very small compared to that of a proton or a neutron.
- Since the nucleus contains protons and neutrons, nearly all of the atom's mass is concentrated in its nucleus.
- Electrical Charges:
- Protons and electrons have electrical charges that are equal and opposite. Protons have a +1 charge, while electrons have a -1 charge.