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
Lesson summary
Lesson summary
- The atom has a nucleus with protons (+) and neutrons (no charge), with electrons (−) moving around it.
- Atomic number = number of protons. Mass number = protons + neutrons.
- In a neutral atom, the number of electrons equals the number of protons.
- In elements with atomic numbers 1 to 20, the first level holds 2 electrons and the second and third levels hold 8 each.
- Losing an electron makes a positive ion; gaining an electron makes a negative ion.
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