Structure of Atom – O Level Notes (Easy Explanation)
Is the atom just a tiny ball? Think again. Understanding the structure of atom is the foundation of all Chemistry. If you can't describe protons, neutrons, and electrons, you can't master Bonding or Stoichiometry.
In this guide, we break down the O Level Chemistry 5070 requirements for Atomic Structure. We explain isotopes, electronic configuration, and how to read the Periodic Table like a pro.
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1. Sub-Atomic Particles (The Building Blocks)
An atom consists of three fundamental particles. You must know their relative mass and charge.
| Particle | Relative Charge | Relative Mass | Location |
|---|---|---|---|
| Proton | +1 | 1 | Nucleus |
| Neutron | 0 | 1 | Nucleus |
| Electron | -1 | 1/1840 (Negligible) | Shells |
Key Definition: The Proton Number (Z) defines the element. Carbon is Carbon because it has 6 protons.
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2. Electronic Configuration (The "Address" of Electrons)
Electrons don't just float randomly. They occupy shells (energy levels). The rule is simple: 2, 8, 8.
- 1st Shell: Max 2 electrons.
- 2nd Shell: Max 8 electrons.
- 3rd Shell: Max 8 electrons.
Example (Sodium Na): Proton Number = 11. Configuration = 2, 8, 1.
Since it has 1 electron in the outer shell, it is in Group I.
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3. Isotopes (Same Element, Different Weight)
Definition: Atoms of the same element with the same number of protons but different numbers of neutrons.
- Same Chemical Properties: Because they have the same number of electrons (valence shell).
- Different Physical Properties: Because they have different masses.
Example: Chlorine-35 and Chlorine-37.
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4. Ions: When Atoms Gain or Lose
Atoms want a full outer shell (Stable Octet). To get it, they lose or gain electrons.
- Metals (Group I, II, III): Lose electrons $\rightarrow$ Positive Ions (Cations).
- Non-Metals (Group V, VI, VII): Gain electrons $\rightarrow$ Negative Ions (Anions).
👉 Cheat Sheet: Download Ion Identification Sheet.
🧪 Visual Guide: Identifying Ions
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Conclusion: Build Your Foundation
The Structure of Atom is the alphabet of Chemistry. Once you know it, you can write the language (formulas and equations). Don't skip the basics.
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