Atom | Nota | Susunan Elektron |
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| 2.1 |
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| 2.8.7 |
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| 2.8.8.2 |
Jadual di bawah menunjukkan susunan elektron bagi 20 unsur yang pertama dalam jadual berkala.
| Unsur | Nombor Proton | Bilangan elektron | Bilangan elektron di dalam | Susunan Elektron | |||
| petala pertama | petala kedua | petala ketiga | petala keempat | ||||
| Hidrogen | 1 | 1 | 1 | 0 | 0 | 0 | 1 |
| Helium | 2 | 2 | 2 | 0 | 0 | 0 | 2 |
| Litium | 3 | 3 | 2 | 1 | 0 | 0 | 2.1 |
| Berillium | 4 | 4 | 2 | 2 | 0 | 0 | 2.2 |
| Boron | 5 | 5 | 2 | 3 | 0 | 0 | 2.3 |
| Karbon | 6 | 6 | 2 | 4 | 0 | 0 | 2.4 |
| Nitrogen | 7 | 7 | 2 | 5 | 0 | 0 | 2.5 |
| Oksigen | 8 | 8 | 2 | 6 | 0 | 0 | 2.6 |
| Fluorin | 9 | 9 | 2 | 7 | 0 | 0 | 2.7 |
| Neon | 10 | 10 | 2 | 8 | 0 | 0 | 2.8 |
| Natrium | 11 | 11 | 2 | 8 | 1 | 0 | 2.8.1 |
| Magnesium | 12 | 12 | 2 | 8 | 2 | 0 | 2.8.2 |
| Aluminium | 13 | 13 | 2 | 8 | 3 | 0 | 2.8.3 |
| Silikon | 14 | 14 | 2 | 8 | 4 | 0 | 2.8.4 |
| Fosforus | 15 | 15 | 2 | 8 | 5 | 0 | 2.8.5 |
| Sulfur | 16 | 16 | 2 | 8 | 6 | 0 | 2.8.6 |
| Klorin | 17 | 17 | 2 | 8 | 7 | 0 | 2.8.7 |
| Argon | 18 | 18 | 2 | 8 | 8 | 0 | 2.8.8 |
| Kalium | 19 | 19 | 2 | 8 | 8 | 1 | 2.8.8.1 |
| Kalsium | 20 | 20 | 2 | 8 | 8 | 2 | 2.8.8.2 |
Jawapan:
Atom | Konfigurasi elektron | Elektron valens |
11Na | 2.8.1 | 1 |
8O | 2.6 | 6 |
12C | 2.8.2 | 2 |
20Ca | 2.8.8.2 | 2 |