Curriculum
Science — First Preparatory
Unit 1: Matter
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Unit 2: Forces
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Unit 3: Life
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Unit 4: Earth and Space
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Text lesson
Structure of the Atom
Structure of the Atom
Arrangement of electrons in energy levels
Arrangement of electrons in energy levels
- Electrons move around the nucleus in levels called shells.
- The maximum number of electrons a level can hold is 2 × n², where n is the level number.
- For elements with atomic numbers 1 to 20, it is enough to know that the first level holds 2 electrons, the second holds 8 and the third holds 8.
- Electrons fill the first level first, then the second, then the third.
- Sodium Na (atomic number 11) has the arrangement 2, 8, 1.
- Chlorine Cl (atomic number 17) has the arrangement 2, 8, 7.
- When an atom loses or gains an electron it becomes an ion.
- A sodium atom loses one electron and becomes the ion Na+, which has 10 electrons.
- A chlorine atom gains one electron and becomes the ion Cl−, which has 18 electrons.
Structure of the Atom · 3 / 6