Structure of Atom – O Level Notes (Easy Explanation)
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📘 Structure of Atom – Simple, Exam-Focused Notes
This chapter connects directly to your O Level Chemistry Syllabus, Chemistry Formula Sheets, and Past Papers.
What is an Atom? (Definition)
An atom is the smallest particle of an element that retains all its chemical properties.
Subatomic Particles
| Particle | Charge | Relative Mass | Position |
|---|---|---|---|
| Proton | +1 | 1 | Nucleus |
| Neutron | 0 | 1 | Nucleus |
| Electron | –1 | 1/1836 | Shells |
Atomic Number (Z)
Number of protons in the nucleus. It defines the identity of an element.
Mass Number (A)
Total number of protons + neutrons.
Isotopes
Atoms of the same element with different number of neutrons.
Example: Carbon-12, Carbon-13, Carbon-14
Electronic Configuration
Students must memorize:
- 1st shell: 2 electrons
- 2nd shell: 8 electrons
- 3rd shell: 8 (or up to 18 for higher levels)
Example: Sodium (11) → 2, 8, 1
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🧪 Fully Solved Past Papers – Structure of Atom Related Questions
IGCSE 0620_m22_qp_62 Solved by Prof. Faisal Janjowa
O Level Chemistry 5070_s23_qp_42 Solved
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